Perovskite ink

Abstract

There is herein provided a perovskite ink comprising: a solvent system comprising: a first solvent, the first solvent being one or more C1-10 alcohol, wherein the solvent system comprises the first solvent in an amount of at least 25 wt%; and one or more perovskite precursors; wherein the perovskite ink and the solvent system do not comprise a toxic solvent. There is further provided a method of forming a perovskite film on a substrate, the method comprising: depositing a layer of the perovskite ink on a substrate; and subsequently at least partially removing the solvent system from the substrate, to thereby cause a perovskite film to form on the substrate.

Description

[0001] 138000GB1 - 1 - Perovskite Ink

[0002] The present disclosure relates to a perovskite ink and a non-toxic solvent system which can be used in the production of a perovskite film. The disclosure extends to a method of forming a perovskite film on a substrate.

[0003] Perovskite solar cells (PSCs) have been reported to deliver high efficiency and superb performance. This is due, at least in part, to the distinctive optoelectronic characteristics of hybrid organic-inorganic perovskite materials, including their high absorption coefficient, direct and tuneable bandgap, long carrier diffusion length and charge mobility. The highest reported efficiency for small area spin-coated perovskite solar cells (PSCs) is now over 26%, comparable to the best performing silicon-based solar cells.

[0004] The possibility of low temperature solution-based manufacturing of PSCs envisages a manufacturing process that is suitable for a high throughput roll-to-roll (R2R) fabrication of PSCs on flexible substrates. The use of light and flexible substrates will additionally lower the balance of system (BOS) costs compared to traditional photovoltaics (PVs) made on heavy and rigid substrates. This will facilitate low-cost harvesting of solar energy and lead to a low levelized cost of electricity (LCOE) as a promising approach to supply the world's rising demand for energy and to reduce the carbon emission.

[0005] So far, the best reported efficiencies have been achieved for PSCs with typical active area sizes of <0.1 cm2. However, increasing the size of solar cells and moving towards mini modules lowers the efficiency values. This is often ascribed to factors such as higher defect density inside the multi-crystalline thin films and larger resistances along the device for charge transfer and extraction. The deposition of thin layers of perovskite materials with high uniformity, purity, and quality over large areas can only be achievable through developing suitable inks designed for scalable deposition techniques.

[0006] Inks used in spin coating process are not suitable for use with scalable deposition methods, such as slot-die coating, ink-jet printing, and more. This is because the latter deposition methods lack the rotational force created during the spin coating, necessary for a quick removal of the solvents from the wet film. Such inks would produce low quality, rough, thin films, with opto-electrical characteristics that are not suitable for use in optoelectronic devices. This highlights the importance and necessity138000GB1 - 2 -for extensive research on the design and development of perovskite precursors suitable for the industry.

[0007] The inclusion of solvents with a low boiling point and high vapour pressure into the precursor solution, along with an optimized gas blowing step after the ink deposition has proven effective for overcoming the above issue. The inventors previously reported that a combination of acetonitrile (ACN) and ethanol (EtOH) could be used as a replacement for commonly used aprotic polar solvents, such as dimethyl formamide (DMF), gamma-butyrolactone (GBL), N-methyl-2-pyrrolidone (NMP), etc. to offer an easier solvent removal through the gas blowing process (see Rezaee, E., et al., Green Solvent Ethanol -Based Inks for Industrially Applicable Deposition of High-Quality Perovskite Films for Optoelectronic Device Applications. Small methods, 2024. 8(2): p.

[0008] 2300564). The functionality of a perovskite precursor produced using this solvent system was shown by fabricating PSCs with a MAPI solution based on the solvent system of ACN / EtOH in a 1:1 volume ratio (ink E50). However, the inventors were not able to completely replace ACN with EtOH due to complications arising from the fast solvent removal step and drying process. In particular, when ACN was not present, films with insufficient nucleation sites were obtained during the gas blowing step after coating, leading to gaps and voids between the crystal grains in the thin layer. This issue stemmed from the lower vapor pressure of EtOH compared to ACN. The fact that ACN is required means that the solvent system cannot be described as non-toxic and would present challenges.

[0009] In particular, on an industrial production line, solvents used in manufacturing of the perovskite thin layers are usually removed through either a gas blowing or heating during the coating process. Production of 1 GW electricity from perovskite solar modules require the consumption of roughly 3500 litres of solvents for a blade-coated perovskite thin film manufacturing line (with power conversion efficiency of 15% for the module). In an ideal condition, the total elimination of toxic solvents (such as ACN) inside the perovskite inks would drastically lower the health and environmental risks of the production process.

[0010] The present invention arises from the inventors' work in attempting to address the problems associated with the prior art.

[0011] In accordance with a first aspect of the invention, there is provided a perovskite ink comprising:

[0012] a solvent system comprising:138000GB1 - 3 - a first solvent, the first solvent being one or more Ci-io alcohol, wherein the solvent system comprises the first solvent in an amount of at least 25 wt%; and

[0013] one or more perovskite precursors;

[0014] wherein the perovskite ink and the solvent system do not comprise a toxic solvent.

[0015] Advantageously, the ink can comprise solely non-toxic solvents. The ink can be used with high throughput manufacturing deposition methods, such as slot-die coating. Additionally, it is also suitable for use with laboratory scale deposition processes such as bar or blade coating. Regardless of the deposition method used, thin layers with superior perovskite quality may be coated over large areas. Additionally, the ink can be used in a deposition process for perovskite thin films which is carried out at room temperature and does not require high temperature post annealing. This means that the ink can be used with both flexible and rigid substrates. In particular, an ink in accordance with the first aspect was used to fabricate perovskite solar modules with different sizes, and efficiencies as high as 18% were achieved.

[0016] Dimethylformamide (DMF), acetonitrile (ACN), N-methyl-2-pyrrolidone (NMP), 2-methoxyethanol (2ME), chlorobenzene (CB) and / or gamma-butyrolactone (GBL) may be understood to be toxic solvents. Accordingly, the perovskite ink and the solvent system may be understood to not comprise a toxic solvent if the perovskite ink and the solvent system do not comprise dimethylformamide (DMF), acetonitrile (ACN), N-methyl-2-pyrrolidone (NMP), 2-methoxyethanol (2ME), chlorobenzene (CB) and / or gamma-butyrolactone (GBL).

[0017] The solvent system may further comprise a second solvent, the second solvent being selected from one or more C2-12 ether, one or more C2-12 ester, one or more C1-10 alcohol or a combination thereof. The solvent system may comprise the second solvent in an amount of at least 30 wt%.

[0018] The solvent system may further comprise a coordinating solvent. The coordinating solvent may be a Lewis base. The coordinating solvent may be dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), l,3-dimethyl-3,4,5,6-tetrahydro-2(lH)-pyrimidinone (DMPU) or a combination thereof. In an embodiment, the coordinating solvent may be DMSO.

[0019] The solvent system may comprise the coordinating solvent in an amount of at least 0.01 wt%, at least 0.1 wt%, at least 0.5 wt%, at least 1 wt%, at least 1.5 wt%, at138000GB1 - 4 -least 2 wt%, at least 2.5 wt% or at least 2.8 wt%. In some embodiments, the solvent system may comprise the coordinating solvent in an amount of at least 3 wt%, at least 5 wt%, at least 10 wt%, at least 15 wt%, at least 20 wt% or at least 25 wt%.

[0020] The solvent system may comprise the coordinating solvent in an amount of less than 50 wt%, less than 45 wt%, less than 40 wt%, less than 38 wt%, less than 36 wt%, less than 34 wt% or less than 32 wt%. In some embodiments, the solvent system may comprise the coordinating solvent in an amount of less than 25 wt%, less than 20 wt%, less than 15 wt%, less than 10 wt%, less than 8 wt%, less than 6 wt%, less than 5 wt%, less than 4.5 wt%, less than 4 wt%, less than 3.8 wt%, less than 3.6 wt% or less than 3.4 wt%.

[0021] The solvent system may comprise the coordinating solvent in an amount of between 0.01 and 75 wt%, between 0.1 and 60 wt%, between 0.5 and 55 wt%, between 1 and 50 wt%, between 1.5 and 45 wt%, between 2 and 40 wt%, between 2.5 and 35 wt% or between 2.8 and 32 wt%. In some embodiments, the solvent system may comprise the coordinating solvent in an amount of between 0.4 and 25 wt%, between 0.6 and 20 wt%, between 0.8 and 15 wt%, between 1 and 10 wt%, between 1.5 and 7.5 wt%, between 2 and 5 wt%, between 2.5 and 4 wt%, between 3 and 3.5 wt% or between 3.2 and 3.4 wt%. In alternative embodiments, solvent system may comprise the coordinating solvent in an amount of between 5 and 50 wt%, between 10 and 40 wt%, between 15 and 38 wt%, between 20 and 36 wt%, between 25 and 34 wt% or between 28 and 32 wt%.

[0022] In some embodiments, the solvent system may substantially consist or consist of the first solvent, the second solvent and optionally the coordinating solvent.

[0023] In some embodiments, the solvent system may substantially consist or consist of the first solvent and optionally the coordinating solvent.

[0024] In some embodiments, the first solvent is a Ci-io alcohol.

[0025] The first solvent may be one or more Ci-6 alcohol, one or more Ci-4 alcohol or one or more C1-2 alcohol. In some embodiments, the first solvent is methanol (MeOH), ethanol (EtOH), 2-propanol (IPA), 1-butanol (1-BuOH) or a combination thereof. In some embodiments, the first solvent is methanol, ethanol or a combination thereof. In some embodiments, the first solvent is ethanol. In some embodiments, the first solvent is methanol.138000GB1 - 5 -

[0026] The solvent system may comprise the first solvent in an amount which is at least 20 wt%, at least 25 wt%, at least 28 wt%, at least 30 wt% or at least 32 wt%. In some embodiments, the solvent system may comprise the first solvent in an amount which is at least 35 wt%, at least 40 wt% or at least 45 wt. In some embodiments, the solvent system may comprise the first solvent in an amount which is at least 50 wt%, at least 55 wt% or at least 60 wt%. In some embodiments, the solvent system may comprise the first solvent in an amount which is at least 65 wt%, at least 70 wt%, at least 75 wt%, at least 80 wt%, at least 85 wt%, at least 90 wt% or at least 95 wt%.

[0027] The solvent system may comprise the first solvent in an amount which is less than 90 wt%, less than 80 wt%, less than 75 wt% or less than 70 wt%. In some embodiments, the solvent system may comprise the first solvent in an amount which is less than 68 wt%, less than 66 wt%, less than 64 wt%, less than 62 wt% or less than 60 wt%. In some embodiments, the solvent system may comprise the first solvent in an amount which is less than 55 wt%, less than 50 wt%, less than 45 wt%, less than 40 wt%, less than 38 wt% or less than 36 wt%.

[0028] The solvent system may comprise the first solvent in an amount which is between 20 and 90 wt%, between 25 and 80 wt%, between 30 and 75 wt% or between 32 and 70 wt%.

[0029] In one embodiment, the solvent system may comprise the first solvent in an amount which is between 32 and 80 wt%, between 34 and 78 wt%, between 36 and 76 wt%, between 38 and 74 wt%, between 40 and 72 wt%, between 42 and 70 wt% or between 44 and 67 wt%. In this embodiment, the first solvent may be as defined above. The first solvent may be methanol, ethanol or a combination thereof. The first solvent may be methanol.

[0030] In an alternative embodiment, the solvent system may comprise the first solvent in an amount which is between 22 and 70 wt%, between 24 and 68 wt%, between 26 and 66 wt%, between 28 and 64 wt%, between 30 and 62 wt% or between 32 and 60 wt%. The solvent system may comprise the first solvent in an amount which is between 35 and 70 wt%, between 40 and 68 wt%, between 45 and 66 wt%, between 50 and 64 wt%, between 52 and 62 wt% or between 54 and 60 wt%. The solvent system may comprise the first solvent in an amount which is between 34 and 58 wt%, between 36 and 56 wt%, between 38 and 54 wt%, between 40 and 52 wt%, between 42 and 50 wt% or between 44 and 48 wt%. The solvent system may comprise the138000GB1 - 6 -first solvent in an amount which is between 22 and 50 wt%, between 24 and 48 wt%, between 26 and 46 wt%, between 28 and 44 wt%, between 30 and 42 wt%, between 32 and 40 wt% or between 34 and 36 wt%. In this embodiment, the first solvent may be as defined above. The first solvent may be methanol, ethanol or a combination thereof. The first solvent may be ethanol.

[0031] In some embodiments, the second solvent is a C2-12 ether, a C2-12 ester or a C1-10 alcohol.

[0032] In some embodiments, the second solvent comprises or consists of one or more C2-12 ether. The second solvent may comprise or consist of or more C3-10 ether, one or more C4-8 ether or one or more C5-6 ether.

[0033] In some embodiments, the ether may be a cyclic ether. Accordingly, the ether may be a compound of formula (I):

[0034]

[0035] wherein n is 0, 1 or 2;

[0036] X is CF R2; and

[0037] R1to R8are each H, methyl or ethyl, with the proviso that R1to R8are selected such that the total number of carbon atoms in the ether does not exceed 12.

[0038] In some embodiments, n is 1.

[0039] In some embodiments, none, one or two of R1to R8are methyl or ethyl and the rest are H. In some embodiments, one of R1to R8is methyl or ethyl and the rest are H. Preferably, one of R1to R8is methyl and the rest are H.

[0040] In some embodiments, R1to R7are each H.

[0041] In some embodiments, R8is methyl.

[0042] In some embodiments, the second solvent comprises or consists of one or more C2-12 ester. The second solvent may comprise or consist of or more C3-10 ester, one or more C3-5 ester or one or more C4 ester.138000GB1 - 7 -

[0043] In some embodiments, the ester may be a compound of formula (II):

[0044] R9COOR10

[0045] (II)

[0046] wherein R9is H, a Ci-io alkyl or a C2-10 alkenyl; and

[0047] R10is a Ci-11 alkyl or a C2-11 alkenyl;

[0048] with the proviso that R9to R10are selected such that the total number of carbon atoms in the ester does not exceed 12.

[0049] R9may be H, a C1-6 alkyl or a C2-6 alkenyl. In some embodiments, R9is a C1-3 alkyl. In some embodiments, R9is methyl.

[0050] R10may be a C1-6 alkyl or a C2-6 alkenyl. In some embodiments, R10is a C1-3 alkyl. In some embodiments, R10is ethyl.

[0051] In embodiments where the second solvent comprises one or more C1-10 alcohol, the one or more C1-10 alcohol of the second solvent may be different to the one or more Ci-10 alcohol of the first solvent. The second solvent may comprise or consist of one or more C2-8 alcohol, one or more C3-6 alcohol or one or more C3-4 alcohol. In some embodiments, the second solvent comprises or consists of 2-propanol (IPA), 1-butanol (1-BuOH) or a combination thereof.

[0052] Accordingly, the second solvent may be selected from the group consisting of 2-methyltetra hydrofuran (2-MeTHF), ethyl acetate (EA), 2-propanol (IPA), 1-butanol (1-BuOH) and a combination thereof. In some embodiments, the second solvent is 2-methyltetra hydrofuran. In some embodiments, the second solvent is ethyl acetate. In some embodiments, the second solvent is 2-propanol. In some embodiments, the second solvent is 1-butanol.

[0053] The solvent system may comprise the second solvent in an amount which is at least 24 wt%, at least 26 wt% or at least 28 wt%. In some embodiments, the solvent system may comprise the second solvent in an amount which is at least 30 wt%, at least 32 wt%, at least 34 wt%, at least 36 wt%, at least 38 wt% or at last 40 wt%. In some embodiments, the solvent system may comprise the second solvent in an amount which is at least 42 wt%, at least 44 wt%, at least 46 wt%, at least 48 wt%, at least 50 wt%, at least 52 wt%, at least 54 wt%, at least 56 wt% or at least 58 wt%.138000GB1 - 8 -

[0054] The solvent system may comprise the second solvent in an amount which is less than 75 wt%, less than 70 wt%, less than 65 wt% or less than 63 wt%. In some embodiments, the solvent system may comprise the second solvent in an amount which is less than 60 wt%, less than 58 wt%, less than 56 wt%, less than 54 wt%, less than 52 wt%, less than 50 wt%, less than 48 wt% or less than 46 wt%. In some embodiments, the solvent system may comprise the second solvent in an amount which is less than 44 wt%, less than 42 wt%, less than 40 wt%, less than 38 wt% or less than 36 wt%.

[0055] The solvent system may comprise the second solvent in an amount which is between 22 and 75 wt%, between 24 and 70 wt%, between 26 and 68 wt% or between 28 and 65 wt%.

[0056] In one embodiment, the solvent system may comprise the second solvent in an amount which is between 25 and 75 wt%, between 30 and 70 wt%, between 32 and 68 wt%, between 34 and 65 wt% or between 36 and 63 wt%. The solvent system may comprise the second solvent in an amount which is between 28 and 48 wt%, between 30 and 46 wt%, between 32 and 44 wt%, between 34 and 42 wt% or between 36 and 40 wt%. The solvent system may comprise the second solvent in an amount which is between 42 and 60 wt%, between 44 and 58 wt%, between 46 and 56 wt%, between 48 and 54 wt% or between 50 and 52 wt%. The solvent system may comprise the second solvent in an amount which is between 52 and 70 wt%, between 54 and 68 wt%, between 56 and 66 wt%, between 58 and 64 wt% or between 60 and 62 wt%. In this embodiment, the first and second solvents may be as defined above. The first solvent may be methanol, ethanol or a combination thereof. The first solvent may be ethanol. The second solvent may comprise or be one or more C2-12 ether. The ether may be a cyclic ether. The cyclic ether may be as defined above. The second solvent may be 2-MeTHF.

[0057] In an alternative embodiment, the solvent system may comprise the second solvent in an amount which is between 22 and 60 wt%, between 24 and 58 wt%, between 26 and 57 wt%, between 28 and 56 wt%, between 30 and 55 wt% or between 32 and 54 wt%. In this embodiment, the first and second solvents may be as defined above. The first solvent may be methanol, ethanol or a combination thereof. The first solvent may be methanol. The second solvent may comprise or be one or more C2-12 ether. The ether may be a cyclic ether. The cyclic ether may be as defined above. The second solvent may be 2-MeTHF.138000GB1 - 9 -

[0058] In a further alternative embodiment, the solvent system may comprise the second solvent in an amount which is between 45 and 70 wt%, between 50 and 68 wt%, between 55 and 66 wt%, between 58 and 64 wt% or between 59 and 62 wt%. In this embodiment, the first and second solvents may be as defined above. The first solvent may be methanol, ethanol or a combination thereof. The first solvent may be ethanol. The second solvent may comprise or be one or more C2-12 ester, one or more C1-10 alcohol or a combination thereof. The ester and / or the alcohol may be as defined above. The second solvent may comprise or be ethyl acetate, 2-propanol, 1-butanol or a combination thereof. The second solvent may be ethyl acetate. The second solvent may be 2-propanol. The second solvent may be 1-butanol.

[0059] The weight ratio of the first solvent to the second solvent may be between 26:74 and 80:20, between 28:72 and 78:22, between 30:70 and 76:24, between 32:68 and 74:26, between 34:66 and 72:28 or between 35:65 and 70:30.

[0060] In an embodiment, the weight ratio of the first solvent to the second solvent may be between 28:72 and 68:32, between 30:70 and 66:34, between 32:68 and 64:36, between 34:66 and 62:38, between 35:65 and 60:40 or between 37:63 and 58:42. The weight ratio of the first solvent to the second solvent may be between 30:70 and 50:50, between 32:68 and 45:55, between 34:66 and 42:58 or between 36:64 and 40:60. The weight ratio of the first solvent to the second solvent may be between 38:62 and 58:42, between 40:60 and 56:44, between 42:58 and 54:46, between 44:56 and 52:48 or between 45:55 and 50:50. The weight ratio of the first solvent to the second solvent may be between 50:50 and 65:35, between 53:47 and 62:38, between 55:45 and 60:40 or between 57:43 and 59:41. In this embodiment, the first and second solvents may be as defined above. The first solvent may be methanol, ethanol or a combination thereof. The first solvent may be ethanol.

[0061] In an embodiment, the weight ratio of the first solvent to the second solvent may be between 40:60 and 76:24, between 42:58 and 74:26, between 43:57 and 72:28, between 44:56 and 70:30 or between 45:55 and 67:33. In this embodiment, the first and second solvents may be as defined above. The first solvent may be methanol, ethanol or a combination thereof. The first solvent may be methanol.

[0062] The one or more perovskite precursors may comprise an ammonium halide, an amidinium halide, a lead halide and / or a caesium halide. In some embodiments, the138000GB1 - 10 -one or more perovskite precursors comprise (i) an ammonium halide and / or an amidinium halide; and (ii) a lead halide.

[0063] In each instance, the halide may be a chloride, a bromide or an iodide.

[0064] The ammonium halide may be a methylammonium halide or a phenylethyl ammonium halide.

[0065] The amidinium halide may be a formamidinium halide.

[0066] Accordingly, the one or more perovskite precursors may comprise methylammonium iodide (MAI), methylammonium bromide (MABr), methylammonium chloride (MACI), phenylethyl ammonium iodide (PEAI), formamidinium iodide (FAI), lead(II) bromide (PbBrz), lead diiodide (Pbh), lead dichloride (PbCIz), caesium iodide (CsI), caesium chloride (CsCI) and / or caesium bromide (CsBr). In some embodiments, the one or more perovskite precursors comprise (i) methylammonium iodide (MAI), methylammonium bromide (MABr), methylammonium chloride (MACI), phenylethyl ammonium iodide (PEAI) and / or formamidinium iodide (FAI); and (ii) lead(II) bromide (PbBrz), lead diiodide (Pbh) and / or lead dichloride (PbCIz).

[0067] In some embodiments, the ammonium halide and / or an amidinium halide is MAI, FAI or a combination thereof. In some embodiments, the ammonium halide and / or an amidinium halide is MAI.

[0068] In some embodiments, the lead halide is Pbb.

[0069] The ammonium halide and / or an amidinium halide may be present at a concentration of at least 0.01 M, at least 0.05 M, at least 0.1 M, at least 0.2 M, at least 0.4 M, at least 0.6 M, at least 0.8 M or at least 0.9 M.

[0070] The ammonium halide and / or an amidinium halide may be present at a concentration of between 0.01 and 10 M, between 0.05 and 5 M, between 0.1 and 3 M, between 0.2 and 2.5 M, between 0.4 and 2 M, between 0.6 and 1.5 M, between 0.8 and 1.2 M or between 0.9 and 1.1 M.

[0071] The lead halide may be present at a concentration of at least 0.01 M, at least 0.05 M, at least 0.1 M, at least 0.2 M, at least 0.4 M, at least 0.6 M, at least 0.8 M or at least138000GB1 - 11 -

[0072] The lead halide may be present at a concentration of between 0.01 and 10 M, between 0.05 and 5 M, between 0.1 and 3 M, between 0.2 and 2.5 M, between 0.4 and 2 M, between 0.6 and 1.5 M, between 0.8 and 1.2 M or between 0.9 and 1.1 M.

[0073] The ink may further comprise a coordinating compound. The coordinating compound may be a Lewis base. The coordinating compound may be an amine. The amine may be methyl amine.

[0074] The ink may comprise the coordinating compound at a concentration of at least 0.05 M, at least 0.1 M, at least 0.5 M, at least 1 M or at least 1.5 M. In some embodiments, the ink may comprise the coordinating compound at a concentration of at least 2 M, at least 2.5 M, at least 3 M, at least 3.5 M, at least 4 M or at least 4.5 M. The ink may comprise the coordinating compound at a concentration of between 0.05 and 20 M, between 0.1 and 15 M, between 0.5 and 12.5 M, between 1 and 10 M or between 1.5 and 9 M. In some embodiments, the ink may comprise the coordinating compound at a concentration of between 2 and 8 M, between 2.5 and 7 M, between 3 and 6.5 M, between 3.5 and 6 M, between 3.75 and 5.75 M, between 4 and 5.5 M, between 4.25 and 5.25 M or between 4.5 and 5 M. In alternative embodiments, the ink may comprise the coordinating compound at a concentration of between 1.1 and 8 M, between 1.2 and 7 M, between 1.3 and 6 M, between 1.4 and 5 M, between 1.5 and 4 M, between 1.6 and 3 M, between 1.8 and 2.5 M or between 1.9 and 2.25 M.

[0075] The ink may further comprise one or more additives. The one or more additives may be configured to improve the crystal grain growth. The one or more additives may be or comprise potassium thiocyanate (KSCN), 2,2'-bipyridyl, methylammonium acetate (MAAc), methylammonium formate (MAFa), 1-adamantylamine and / or lead(II) thiocyanate (Pb(SCN)2). In an embodiment, the one or more additives is KSCN. In an embodiment, the one or more additives is 2,2'-bipyridyl.

[0076] The ink may comprise the additive at a concentration of at least 0.001 M, at least 0.002 M, at least 0.004 M, at least 0.006 M, at least 0.008 M, at least 0.01 M, at least 0.02 M. In some embodiments, the ink may comprise the additive at a concentration of at least 0.03 M or at least 0.04 M.

[0077] The ink may comprise the additive at a concentration of between 0.001 and 1 M, between 0.002 and 0.5 M, between 0.004 and 0.3 M, between 0.006 and 0.25 M, between 0.008 and 0.2 M, between 0.01 and 0.15 M or between 0.02 and 0.1 M. In138000GB1 - 12 -some embodiments, the ink may comprise the additive at a concentration of between 0.03 and 0.08 M or between 0.04 and 0.06 M. In alternative embodiments, the ink may comprise the additive at a concentration of between 0.008 and 0.06 M, between 0.01 and 0.05 M or between 0.02 and 0.04 M.

[0078] In accordance with a second aspect, there is provided the use of a solvent system in the manufacture of a perovskite film, the solvent system comprising:

[0079] a first solvent, the first solvent being one or more Ci-io alcohol, wherein the solvent system comprises the first solvent in an amount of at least 25 wt%; wherein the solvent system does not comprise a toxic solvent.

[0080] The solvent system may be as defined in relation to the first aspect.

[0081] In accordance with a third aspect, there is provided a method of forming a perovskite film on a substrate, the method comprising:

[0082] depositing a layer of a perovskite ink on a substrate, wherein the perovskite ink is as defined in the first aspect; and

[0083] subsequently at least partially removing the solvent system from the substrate, to thereby cause a perovskite film to form on the substrate.

[0084] Advantageously, the method of the third aspect can provide a high-quality perovskite film over a large surface area.

[0085] The substrate may comprise a first side. The layer of perovskite ink may be deposited on the first side of the substrate.

[0086] The substrate may be a flexible substrate or a rigid substrate.

[0087] In some embodiments, the substrate is a rigid substrate. The rigid substrate may comprise a glass substrate.

[0088] In some embodiments, the substrate is a flexible substrate. The flexible substrate may comprise a foil or a flexible glass substrate. The foil may be a polymer based plastic foil or a metal based foil. The polymer based plastic foil may be polyethylene terephthalate (PET), polyethylene naphthalate (PEN) or polyimide (PI). The flexible glass substrate may be Willow glass.138000GB1 - 13 - The substrate may comprise a conductive layer. The conductive layer may be disposed on the first side of the substrate. The conductive layer may be a layer of a metal oxide, a carbon-based electrode material, a nano-wire based electrode, a thin metal-based material, or a combination thereof. The metal oxide may be indium tin oxide (ITO), fluorine tin oxide (FTO), aluminium doped zinc oxide (AZO), or a combination thereof. The carbon-based electrode material may be graphene oxide, graphene, carbon, carbon nanotubes (CNTs) or a combination thereof. The CNTs may be single walled CNTs or multi walled CNTs. The nano-wire based electrode may comprise silver nanowires (Ag-NWs). The thin metal material may comprise of silver, copper, zinc or a combination thereof.

[0089] In some embodiments, the substrate is a glass / ITO substrate.

[0090] Prior to depositing the layer of perovskite ink on the substrate, the method may comprise cleaning the substrate.

[0091] Cleaning the substrate may comprise washing the substrate. The substrate may be washed with one or more cleaning liquids. The substrate may be washed with at least one, at least two, at least three or at least four cleaning liquids. The substrate may be washed with between one and ten cleaning liquids, between two and six cleaning liquids or between three and five cleaning liquids.

[0092] In embodiments where the substrate is washed with more than one cleaning liquids, the substrate may be washed with each cleaning liquid sequentially. Accordingly, the substrate may be washed with a first cleaning liquid and then subsequently washed with a second cleaning liquid. The substrate may subsequently be washed with a third cleaning liquid. The substrate may subsequently be washed with a fourth cleaning liquid.

[0093] In some embodiments, the substrate is ultrasonicated with the one or more cleaning liquids. The substrate may be disposed in an ultrasonic bath with the cleaning liquid and ultrasonicated. In embodiments where the substrate is washed with more than one cleaning liquids, the substrate may disposed in an ultrasonic bath and ultrasonicated with each cleaning liquid sequentially.

[0094] The substrate may be ultrasonicated for at least 30 seconds, at least 1 minute, at least 2 minutes, at least 3 minutes, at least 4 minutes or at least 5 minutes. The substrate may be ultrasonicated for between 30 seconds and 1 hour, between 1 and138000GB1 - 14 - 30 minutes, between 2 and 20 minutes, between 3 and 10 minutes or between 4 and 6 minutes.

[0095] The substrate may be washed at a temperature of between 0 and 100°C, between 5 and 50°C, between 10 and 30°C or between 15 and 25°C.

[0096] The or each cleaning liquid may comprise a solvent. The solvent may comprise water and / or an organic solvent. The water may be deionised water. The organic solvent may comprise a C3-6 ketone and / or a C1-6 alcohol. In some embodiments, the ketone is acetone. The alcohol may be methanol, ethanol, 1-propanol or 2-propanol. In some embodiments, the alcohol is 2-propanol.

[0097] The cleaning liquid may comprise a detergent. The detergent may be an alkaline detergent. The detergent may be present in an amount of at least 0.1 wt%, at least 0.5 wt%, at least 1 wt%, at least 2 wt% or at least 3 wt%. The detergent may be present in an amount of between 0.1 and 50 wt%, between 0.5 and 30 wt%, between 1 and 20 wt%, between 2 and 15 wt% or between 3 and 10 wt%.

[0098] In some embodiments, the first cleaning liquid comprises water. In some embodiments, the first cleaning liquid comprises the detergent.

[0099] In some embodiments, the second cleaning liquid comprises water. In some embodiments, the second cleaning liquid consists substantially of water.

[0100] In some embodiments, the third cleaning liquid comprises an organic solvent. In some embodiments, the third cleaning liquid consists substantially of the organic solvent. The organic solvent may be a C3-6 ketone. The ketone may be acetone.

[0101] In some embodiments, the fourth cleaning liquid comprises an organic solvent. In some embodiments, the fourth cleaning liquid consists substantially of the organic solvent. The organic solvent may be a C1-6 alcohol. The alcohol may be methanol, ethanol, 1-propanol or 2-propanol. In some embodiments, the alcohol is 2-propanol.

[0102] Subsequent to washing the substrate, the method may comprise drying the substrate.

[0103] The substrate may be dried under a gas stream. The gas stream may be an inert gas stream. The gas stream may be a nitrogen gas stream.138000GB1 - 15 - Alternatively, or additionally, the substrate may be dried at an elevated temperature. This may be referred to as annealing the substrate. In some embodiments, the substrate may be dried at an elevated temperature subsequent to being dried under a gas stream. It may be appreciated that the elevated temperature may be selected by the skilled person, and may depend upon the substrate. For instance, if the substrate comprises a plastic, the elevated temperature may not exceed the glass transition temperature. The elevated temperature may be a temperature of at least 30°C, at least 40°C, at least 50°C, at least 60°C, at least 70°C, at least 80°C, at least 90°C, at least 100°C, at least 110°C, at least 120°C or at least 130°C. The duration of time which the substrate is dried at the elevated temperature may also be selected by the skilled person. For instance, the substrate may be dried at the elevated temperature for at least 30 seconds, at least 1 minute, at least 2 minutes, at least 4 minutes, at least 6 minutes, at least 8 minutes or at least 10 minutes. The substrate may be dried at the elevated temperature for between 30 seconds and 2 hours, between 1 and 60 minutes, between 2 and 30 minutes, between 4 and 20 minutes, between 6 and 15 minutes or between 8 and 12 minutes.

[0104] Alternatively, or additionally, cleaning the substrate may comprise conducting a UV-ozone treatment, a plasma treatment and / or a corona treatment on the substrate. The UV-ozone treatment, the plasma treatment and / or the corona treatment may be conducted on the first side of the substrate. The plasma treatment and / or corona treatment may be an O2 plasma treatment and / or O2 corona treatment. The method may comprise conducting the UV-ozone treatment, plasma treatment and / or corona treatment for at least 30 seconds, at least 1 minute, at least 2 minutes, at least 4 minutes, at least 6 minutes, at least 8 minutes or at least 10 minutes. The method may comprise conducting the UV-ozone treatment, plasma treatment and / or corona treatment for between 30 seconds and 2 hours, between 1 and 60 minutes, between 2 and 30 minutes, between 4 and 20 minutes, between 6 and 15 minutes or between 8 and 12 minutes.

[0105] In an embodiment, cleaning the substrate comprises washing the substrate and conducting a UV-ozone treatment on the substrate. Cleaning the substrate may comprises washing the substrate and subsequently conducting a UV-ozone treatment on the substrate. Cleaning the substrate may comprise washing the substrate, drying the substrate and subsequently conducting a UV-ozone treatment on the substrate.

[0106] The method may comprise depositing one of one or more hole-transporting layers (HTLs) and one or more electron transport layers (ETLs) prior to depositing the layer138000GB1 - 16 -of the perovskite ink on the substrate and depositing the other of the one or more HTLs and one or more ETLs on the substrate subsequent to causing a perovskite film to form on the substrate. The one or more HTLs and one or more ETLs may each be deposited on the first side of the substrate. The layer of perovskite ink may be deposited on the one or more HTLs or the one or more ETLs.

[0107] In embodiments where the method comprises cleaning the substrate, the method may comprise cleaning the substrate and subsequently depositing the one or more HTLs and one or more ETLs on the substrate.

[0108] In one embodiment, the method comprises:

[0109] optionally cleaning the substrate;

[0110] subsequently depositing the one or more HTLs on the substrate; subsequently depositing the layer of perovskite ink on the substrate; subsequently at least partially removing the solvent system from the substrate, to thereby cause a perovskite film to form on the substrate; and

[0111] subsequently depositing the one or more ETLs on the substrate.

[0112] It may be appreciated that if the method comprises depositing one or more HTLs prior to depositing the layer of perovskite ink, as defined in the above embodiment, then the method produces a p-i-n device.

[0113] In an alternative embodiment, the method comprises:

[0114] optionally cleaning the substrate;

[0115] subsequently depositing the one or more ETLs on the substrate; subsequently depositing the layer of perovskite ink on the substrate; subsequently at least partially removing the solvent system from the substrate, to thereby cause a perovskite film to form on the substrate; and

[0116] subsequently depositing the one or more HTLs on the substrate.

[0117] It may be appreciated that if the method comprises depositing one or more ETLs prior to depositing the layer of perovskite ink, as defined in the above embodiment, then the method produces a n-i-p device.

[0118] In embodiments where more than one HTL is deposited on the substrate, each may be deposited sequentially on the substrate. The method may comprise depositing one, two, three or four HTLs on the substrate. In an embodiment, the method comprises depositing one HTL on the substrate.138000GB1 - 17 -

[0119] The or each HTL may independently comprise one or more inorganic hole transporting material (HTM) and / or one or more organic HTM. The inorganic HTM may be selected from the group consisting of a metal oxide, a copper-based material (e.g. CuOx, CuSCN or Cui), a nickel-based material (e.g. NiOx) and a two-dimensional layered material (e.g. M0S2 or WS2). The organic HTM may be selected from the group consisting of a self-assembled monolayer (SAM) and a polymer. The SAM may be [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz), (4-(3,6-dimethoxy-9H-carbazol-9-yl)butyl)phosphonic acid (MeO-4PACz), spiro-OMeTAD, Me-2PACz, MeO-2PACz or 2PACz. The polymer may be P3HT, PTAA or PEDOT:PSS.

[0120] In some embodiments, the HTL comprises an organic HTM. In some embodiments, the organic HTM is a SAM. In some embodiments, the SAM is Me-4PACz.

[0121] The or each HTL layer may be deposited on the substrate using any method known in the art. The or each HTL layer may be thermally deposited, sputter deposited or deposited from a solution phase. In embodiments where an HTL is deposited from a solution phase it may be deposited using slot-die coating, bar coating, ink-jet printing, spray coating or gravure printing.

[0122] In an embodiment, depositing the HTL layer on the substrate comprises depositing SAM solution on the substrate, wherein the SAM solution comprises a SAM and a solvent, and subsequently removing the solvent therefrom to form a HTL on the substrate. The SAM solution may be deposited on the substrate using slot-die coating, bar coating or blade coating.

[0123] The solvent may be an organic solvent. The organic solvent may be an C1-6 alcohol. The C1-6 alcohol may be methanol, ethanol, 1-propanol or 2-propanol. In an embodiment, the C1-6 alcohol is ethanol. The SAM solution may comprise the SAM at a concentration of at least 0.01 x 10'3M, at least 0.1 x 10'3M, at least 0.5 x 10'3M or at least 0.8 x 10'3M. The SAM solution may comprise the SAM at a concentration of between 0.01 x 10'3M and 10 x 10'3M, between 0.1 x 10'3M and 5 x 10'3M, between 0.5 x 10'3M and 2 x 10'3M or between 0.8 x 10'3M and 1.2 x 10'3M.

[0124] Removing the solvent may comprise contacting the SAM solution on the substrate and a gas stream. The gas stream may be an inert gas stream. The gas stream may be a nitrogen gas stream.138000GB1 - 18 - Subsequent to removing the solvent from the SAM solution, the method may comprise annealing the substrate. Annealing the substrate may comprise heating the substrate to an elevated temperature. The elevated temperature may be a temperature of at least 30°C, at least 40°C, at least 50°C, at least 60°C, at least 70°C, at least 80°C, at least 90°C, at least 100°C or at least 110°C. The elevated temperature may be a temperature of between 40 and 300°C, between 50 and 250°C, between 60 and 200°C, between 70 and 175°C, between 80 and 150°C, between 90 and 140°C, between 100 and 130°C or between 110 and 120°C. The substrate may be held at the elevated temperature for at least 30 seconds, at least 1 minute, at least 2 minutes, at least 4 minutes, at least 6 minutes, at least 8 minutes or at least 10 minutes. The substrate with the layer of perovskite ink may be held at the elevated temperature for between 30 seconds and 2 hours, between 1 and 60 minutes, between 2 and 30 minutes, between 4 and 20 minutes, between 6 and 15 minutes or between 8 and 12 minutes.

[0125] The or each ETL may independently comprise one or more inorganic electron transporting material (ETM) and / or one or more organic ETM. The inorganic ETM may a metal oxide (e.g. ZnO, SnC>2 or TiOz). The organic ETM may be selected from the group consisting of a fullerene (e.g. Ceo or C70) or a derivative thereof, or an organic compound (e.g. bathocuproine (BCP)). The derivative of a fullerene may be phenyl-C61-butyric acid methyl ester (PCBM), bis(l-[3-(methoxycarbonyl)propyl]-l-phenyl)-[6,6]C62 (bis-PCBM), [6,6]-phenyl-C61 butyric acid n-hexyl ester (PCBC6) or [6,6]-phenyl-C61 butyric styryl dendron ester (PCBSD).

[0126] The one or more ETLs may comprise one, two, three or four ETLs. In some embodiments, the one or more ETLs comprise two ETLs.

[0127] In an embodiment, a first ETL is a fullerene or a derivative thereof. The first ETL may be Ceo-

[0128] In an embodiment, a second ETL is an organic compound or a metal oxide. The second ETL may be BCP.

[0129] In an embodiment, the first ETL may be deposited on the perovskite film. The second ETL may be deposited on the first ETL.

[0130] The or each ETL layer may be deposited on the substrate using any method known in the art. The or each ETL layer may be thermally deposited, sputter deposited or138000GB1 - 19 -deposited from a solution phase. In embodiments where an ETL is deposited from a solution phase it may be deposited using slot-die coating, bar coating, ink-jet printing, spray coating or gravure printing.

[0131] In an embodiment, the method may comprise thermally depositing the one or more ETLs on the perovskite film. The ETLs may be thermally deposited in a vacuum deposition chamber. In embodiments where the method comprises depositing two or more ETLs, each ETL may be deposited sequentially.

[0132] The or each ETL may define a thickness of at least 0.1 nm, at least 0.5 nm, at least 1 nm, at least 2 nm, at least 3 nm, at least 4 nm or at least 5 nm. The or each ETL may define a thickness of between 0.1 and 500 nm, between 0.5 and 250 nm, between 1 and 100 nm, between 2 and 75 nm, between 3 and 50 nm, between 4 and 40 nm or between 5 and 30 nm.

[0133] Depositing the layer of perovskite ink on the substrate may comprise slot-die coating, bar coating or blade coating the layer of perovskite ink on the substrate. In an embodiment, the method comprises bar coating the layer of perovskite ink on the substrate.

[0134] Depositing the layer of perovskite ink on the substrate may comprise depositing the layer of perovskite ink on the substrate such that the layer of perovskite ink defines a thickness of between 10 pm and 1 mm, between 50 and 750 pm, between 100 and 500 pm, between 125 and 300 pm or between 150 and 200 pm.

[0135] The layer of the perovskite ink may be deposited at a thickness sufficient to provide a perovskite film with a thickness between 50 nm and 1 mm, between 100 nm and 500 pm, between 200 nm and 100 pm, between 300 nm and 10 pm, between 400 nm and 1 pm or between 500 and 900 nm.

[0136] Partially removing the solvent system from the substrate may comprise contacting the layer of perovskite ink on the substrate and a gas stream. The gas stream may be an inert gas stream. The gas stream may be a nitrogen gas stream.

[0137] Advantageously, the gas stream causes fast solvent removal which can guarantee enough nucleation sites form inside the drying film, resulting in crystal grains with micrometre size.138000GB1 - 20 - The method may comprise contacting the layer of perovskite ink on the substrate and the gas stream directly after the layer of perovskite ink has been deposited on the substrate. It may be understood that the layer of perovskite ink on the substrate was contacted with the gas stream directly after the layer of perovskite ink has been deposited on the substrate if the layer of perovskite ink on the substrate was contacted with the gas stream less than 10 minutes, less than 8 minutes, less than 6 minutes, less than 4 minutes, less than 2 minutes, less than 1 minute, less than 45 seconds, less than 30 seconds, less than 15 seconds, less than 10 seconds or less than 5 seconds after the layer of perovskite ink had finished being deposited on the substrate.

[0138] The method may comprise heating the substrate with the layer of perovskite ink thereon to an elevated temperature, and thereby annealing the perovskite film.

[0139] The elevated temperature may be a temperature of at least 30°C, at least 40°C, at least 50°C, at least 60°C, at least 70°C, at least 80°C, at least 90°C or at least 100°C. The elevated temperature may be a temperature of between 50 and 150°C, between 60 and 140°C, between 70 and 130°C, between 80 and 120°C or between 90 and 110°C.

[0140] The substrate with the layer of perovskite ink may be held at the elevated temperature for at least 30 seconds, at least 1 minute, at least 2 minutes, at least 4 minutes, at least 6 minutes, at least 8 minutes or at least 10 minutes. The substrate with the layer of perovskite ink may be held at the elevated temperature for between 30 seconds and 2 hours, between 1 and 60 minutes, between 2 and 30 minutes, between 4 and 20 minutes, between 6 and 15 minutes or between 8 and 12 minutes.

[0141] The substrate with the layer of perovskite ink thereon may be heated using a hot plate, a hot gas (e.g. air or an inert gas), IR heating, a flashlamp or a combination thereof.

[0142] The method may comprise heating the substrate with the layer of perovskite ink thereon to the elevated temperature simultaneously to contacting the layer of perovskite ink on the substrate and the gas stream.

[0143] The method may comprise depositing one or more electrode layers on the substrate. The method may comprise depositing the one or more electrode layers on the first side of the substrate. The one or more electrode layers may be deposited subsequent138000GB1 - 21 -to the perovskite film forming on the substrate. The one or more electrode layers may be deposited subsequent to depositing the one or more HTLs and the one or more ETLs. In some embodiments, the method may comprise depositing the one or more electrode layers on the one or more HTLs or the one or more ETLs.

[0144] The method may comprise depositing one or two electrode layers on the substrate. In an embodiment, the method comprises depositing one electrode layer on the substrate.

[0145] The one or more electrode layers may comprise or be a metal, a carbon based electrode material, a metal oxide, or a combination thereof. The metal may comprise or be silver, copper, gold or chromium. The metal oxide may be indium tin oxide (ITO), fluorine tin oxide (FTO), aluminium doped zinc oxide (AZO) or a combination thereof. The carbon-based electrode material may be graphene oxide, graphene, carbon, carbon nanotubes (CNTs) or a combination thereof. The CNTs may be single walled CNTs or multi walled CNTs.

[0146] The method may comprise depositing the one or more electrode layers using any method known in the art. For instance, the method may comprise thermally depositing, sputter depositing, printing (e.g. screen printing) or coating (e.g. bar coating or slot die coating) the or each electrode layer on the substrate. In some embodiments, the method may comprise thermally depositing the or each electrode layer on the substrate. The electrode layer may be thermally deposited in a vacuum deposition chamber.

[0147] Depositing the electrode layer on the perovskite film or the one or more ETLs may comprise depositing the electrode layer such that the electrode layer defines a thickness of between 1 nm and 1 mm, between 10 nm and 100 pm, between 20 nm and 10 pm, between 30 nm and 1 pm, between 40 and 500 nm, between 50 and 200 nm, between 60 and 175 nm, between 70 and 150 nm or between 80 and 120 nm.

[0148] Advantageously, the method of the third aspect can provide a perovskite solar cell (PSC).

[0149] All features described herein (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined with any of the above aspects in any combination, except combinations where at least some of such features and / or steps are mutually exclusive.138000GB1 - 22 -

[0150] For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Figure 1 is a flowchart illustrating the approach used in this study to employ Hansen Solubility Parameters in Practice (HSPiP) software for finding an optimised solvent volume ratio for a non-toxic perovskite ink;

[0151] Figure 2 shows (a) a scanning electron microscope (SEM) image of the surface of a methylammonium lead iodide (MAPI)-based perovskite film produced using an ink in accordance with the present invention and bar coated on top of glass / indium tin oxide (ITO) substrate; (b) an SEM cross-section image of the perovskite film; and (c) an atomic force microscope (AFM) image of the perovskite film;

[0152] Figure 3 shows (a) an X-ray diffraction (XRD) spectrum of a perovskite thin film bar coated on top of glass / ITO substrate; and (b) steady-state and (c) time-resolved photoluminescence spectra of a perovskite thin layer bar coated on top of either a glass / ITO or glass / ITO / self-assembled monolayer (SAM) substrate where excitation is performed on the perovskite layer side;

[0153] Figure 4 shows the steady-state photoluminescence spectra of a perovskite thin layer bar coated on top of glass / ITO and glass / ITO / SAM substrates where excitation is performed on glass side;

[0154] Figure 5 shows (a) an image of a fabricated perovskite solar module (PSM) with four sub-cells, connected in series and the active area of 3.8 cm2; (b) a cross-section SEM image of the PSM device; (c) the statistics of the performance parameters for 20 PSM devices and (d) the current-voltage (JV) curves for a champion PSM devices based on NT MAPI ink, and two different SAMs as HTLs: Me-4PACz and MeO-4PACz;

[0155] Figure 6 shows (a) the JV curves for the champion PSM device based on NT MAPI ink, with 7 sub-cells connected in series and the active area of 11.515 cm2; and (b) the statistics of the performance parameters for 16 PSM devices;

[0156] Figure 7 shows top surface SEM images of perovskite thin layers fabricated on glass / ITO substrates (5x5 cm2), using bar coating technique. Thin layers obtained from non-toxic inks with solvent system of MeTHF:EtOH:DMSO 39:58:3, and the perovskite composition of (a) MAPbI2.95Br0.05 (containing 5% MABr); (b) PEAo.o5MAo.95PbI3(containing 5% PEAI); and (c) MAPbh.gBro.i (containing 5% PbBrz). Perovskite films fabricated using ink with the solvents systems of (d) Ethyl acetate / EtOH / DMSO 48:49:3; (e) IPA / EtOH / DMSO 49:48:3; and (f) 1-Butanol / EtOH / DMSO 49:48:3. Perovskite films fabricated using ink with the solvents systems of (g) MeTHF / MeOH / DMSO 49:48:3; and (h) MeTHF / MeOH / DMSO 29:68:3. Thin films obtained from non-toxic inks with solvent system of MeTHF / EtOH / DMSO138000GB1 - 23 - 31:49:20, and FAMA-based perovskites with the compositions of (i) MAo.sFAo. Pbh; and (j) MAo.sFAo.sPbh. Scale bars represent 1 pm; and

[0157] Figure 8 shows photographs of a perovskite thin film deposited on top of a PET / ITO substrate showing (a) the top side and (b) the rear (buried) side of sample; also provided are (c+d) two surface SEM images with different magnification.

[0158] Materials

[0159] The materials used were sourced from various suppliers. ITO coated glass substrates (15 sq'1, 50 mm x 50 mm x 0.9 mm) were obtained from Yingkou Shangneng Photoelectric Material Co., Ltd. Lead diiodide (Pbb, 99.99%) and lead bromide (PbBrz, >98%) were purchased from TCI (Tokyo Chemical Industry). Methylamine solution (2.0 M in methanol) was also acquired from TCI, while methylamine solution (33 wt% in ethanol) was sourced from Sigma Aldrich. Methylammonium iodide (MAI), formamidinium iodide (FAI), phenylethylammonium iodide (PEAI), and methylammonium bromide (MABr) were supplied by GreatCell Solar Materials.

[0160] Potassium thiocyanate, 2-methyl tetra hydrofuran (2MeTHF), isopropanol (IPA), ethanol (EtOH), acetone, dimethyl sulfoxide (DMSO), chlorobenzene (CB) and 1-butanol (BuOH) were all purchased from Sigma Aldrich. Additionally, C60 and bathocuproine (BCP, sublimed grade >99.5%) were purchased from Ossila. 2, 3, 5, 6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) was purchased from Xi'an Polymer Light Technology Corp. Me-4PACz and MeO-4PACz were sourced from TCI.

[0161] Example 1 - Non-Toxic (NT) perovskite ink development

[0162] The inventors previously demonstrated the possibility to use ethanol (EtOH) as a nontoxic solvent for perovskite inks by replacing up to 70% of acetonitrile (ACN) with ethanol (EtOH) (see Rezaee, E., et al., Green Solvent Ethanol-Based Inks for Industrially Applicable Deposition of High-Quality Perovskite Films for Optoelectronic Device Applications. Small methods, 2024. 8(2): p. 2300564). However, the inventors were not able to completely replace ACN with EtOH. The inventors wished to incorporate a new solvent to fully replace ACN from the solvent system. However, there are countless solvent alternatives, which makes the identification of the right solvent similar to "finding a needle in a haystack".

[0163] To attempt to identify a suitable replacement solvent, modelling of the most appropriate solvent system was carried out using the Hansen Solubility Parameters (HSP). First, the components of the inventors' previously best performing perovskite ink E50 were introduced in the Hansen Solubility Parameters in Practice (HSPiP) software for the calculation of energy-related parameters. The Hansen HSPiP program138000GB1 - 24 -is designed to identify the optimal solvent mixture based on the interaction energy between solvents and solute. This energy is divided into three primary components: dispersion energy (3D), hydrogen bonding ability energy (6H), and polarity energy (6P). The program is known for its reliability and reproducibility, consistently aligning with experimental data. The obtained parameters for E50 are 3D: 15.6, 3P: 13.4, and 3H: 12.8. Based upon these parameters, the inventors then identified a few promising green solvents that could potentially be suitable for replacing ACN. Based on the modelling results, 2-methyl tetra hydrofuran (2MeTHF) was selected as a non-toxic solvent alternative to ACN.

[0164] It is noted that 2MeTHF may be viewed as having low toxicity, as evidenced by the high permitted daily exposure (PDE) value of 50 mg / day. This is much higher than the PDE values for other commonly used for perovskite layer deposition, such as dimethylformamide (DMF), acetonitrile (ACN), N-methyl-2-pyrrolidone (NMP), 2-methoxyethanol (2ME) and chlorobenzene (CB), see Table 1.

[0165] Table 1 - Toxicity and work exposure limit information for several commonly used solvents for perovskite ink as well as ethanol and MeTHF

[0166]

[0167] avalues taken from Ball, D.J. and W.P. Beierschmitt, Permitted daily exposure values: application considerations in toxicological risk assessments. International Journal of Toxicology, 2020. 39(6): p. 577-585.138000GB1 - 25 -bvalue taken from Parris, P., et al., Calculation of a permitted daily exposure value for the solvent 2-methyltetrahydrofuran. Regulatory Toxicology and Pharmacology, 2017.

[0168] 87: p. 54-63.

[0169] Furthermore, 2MeTHF is considered a green solvent. This is because it can be derived from renewable sources, such as levulinic acid or furfural, and is biodegradable, converting into renewable sources in the presence of sunlight and air. Additionally, 2MeTHF has low solubility in water, reducing its impact on wastewater pollution while facilitating its recovery and reuse.

[0170] The process for identifying the optimal solvent blend for perovskite materials is illustrated in the flowchart shown in Figure 1. Briefly, the reference point was defined as being the values known for ink E50, i.e. HSP parameters 3D: 15.6, 6P: 13.4 and 6H: 12.8 (step 1). EtOH and MeTHF were selected as being the non-toxic solvents of interest. The software was used to choose the best combination of EtOH and 2MeTHF with the closest HSP parameters (steps 2 and 3). The suggested combination was 33 vol% of 2MeTHF and 67 vol% of EtOH, resulting in the HSP parameters of 3D: 16, 3P: 7.5 and 3H: 14.5 (step 4). It was confirmed by experimentation that this solvent system was suitable (step 5). The inventors further optimized the volume ratio of the main solvents and added a small amount of DMSO as a coordinating solvent to achieve the most reliable ink recipe for high-quality perovskite thin layers (step 6). The final solvent system includes 59 vol% EtOH, 39 vol% 2MeTHF, and 2 vol% DMSO. The calculated HSP parameters for this optimized non-toxic (NT) ink are 3D: 16.1, 3P: 7.4, and 3H: 13.5 (step 7). This was tested, as described below (step 8). A small amount of potassium thiocyanate (KSCN) was added to the final ink (with the concentration of 0.05 mmol / mL) to improve the crystal grain growth. This helps reducing the grain boundaries and therefore provides a lower number of recombination sites inside the film.

[0171] Introducing methyl amine (MA°) molecules into the perovskite precursor mixture in a solvent blend can form a coordination complex (MAPb ’xMA) through dative coordination bonds between MAPI and MA° molecules. The coordination complex subsequently offers a higher solubility in the range of selected solvents, which are generally considered anti-solvents for perovskite precursors. This strategy provides two advantages: first, a wider range of solvents can be explored to find the optimized and non-toxic solvent blend; second, HSPiP software is designed for non-ionic (molecular) solutes, offers more accurate results when dealing with such molecules. MA° molecules can be introduced either through an MA° gas blowing process, or by138000GB1 - 26 -dissolving them in one of the solvents (in this case, ethanol). In the solvent system used, the ethanol contained 33 wt% MA°.

[0172] Additionally, lead diiodide (Pbh) was also included in the ink to both act as a precursor and to help passivate a range of defects inside a bulk film.

[0173] The composition of the ink used to produce perovskite film is provided in Table 2 below.

[0174] Table 2 - Composition of perovskite ink

[0175]

[0176] The ink was produced by adding 1 mmol of MAI and 1 mmol of Pbh into a solvent mixture comprising 390 pL of Me-THF and 590 pL of EtOH (containing 33 wt% MA). Additionally, 28 mol% (20 pL) of DMSO, and 0.05 mmol of KSCN were added into the mixture. The perovskite mixture was shaken for 5 minutes until all the precursors were completely dissolved in the solvent mixture, and the perovskite ink with the concentration of 1 M was achieved. The perovskite ink was filtered using 0.20 pm PTFE micro filter before use.

[0177] Example 2 - Perovskite thin film characterization

[0178] MAPI perovskite thin layers were bar coated on top of glass / ITO substrate using the newly developed NT ink described in Table 2.

[0179] Perovskite samples were fabricated on ITO-coated glass substrates using a modified slot-die coater from Ossila, which was adapted to function as a bar coater. A smooth stainless-steel bar was utilized for the coating process, with the gap between the bar and the substrate adjusted using micrometer screws. An Exair Super Air Knife was positioned 15 cm above the substrate on the downstream side of the coating bar. Nitrogen gas, at a pressure of 3 bar, was used as the feed gas. The substrates138000GB1 - 27 -underwent a sequential cleaning process, spending 5 minutes in an ultrasonic bath with deionized water and Helmanex III detergent (3-10 wt%), 5 minutes with deionized water, 5 minutes with acetone and finally 5 minutes with isopropanol. This was followed by a vigorous nitrogen gas blowing for quick drying the sample surface, and a 10-minute UV-ozone treatment prior to film deposition. The coating dimensions were tailored to the substrate size, with a coating gap of 150-200 pm set between the bar and the substrates. Ink was pipetted into this gap until it was completely filled. For 5 cm x 5 cm glass substrates, 35 pL of the NT MAPI precursor was used. The coating process was performed at room temperature in a nitrogen-filled glove box, with a variable speed ranging from 20 to 22 mm / s. Three seconds after the coating process concluded, the nitrogen gas blowing step was activated. The perovskite films were then annealed at 100°C for 10 minutes.

[0180] To achieve fully packed crystal grains inside the film, a nucleation-driven mechanism is necessary during the film formation process. Fast solvent removal through a gas blowing step can guarantee enough nucleation sites form inside a drying film, resulting in crystal grains with micrometre size. SEM images captured from the surface of the MAPI films noticeably suggest the superior quality of the film, delivering enlarged crystal grains, a smooth surface and a lack of voids and pinholes in between the grains (see Figure 2a). The presence of packed grains indicates the controlled lateral crystal growth process, which was delivered using additives such as the coordinating solvent (DMSO), as well as the additive KSCN inside the NT ink. These characteristics are crucial for achieving high performance of the films in various potential applications. The cross-section SEM image additionally shows the absence of grain boundaries through the thickness of the film, ensuring the smooth transfer of generated charges to the adjacent charge collecting layer within a single crystal (Figure 2b). To achieve a high-performance device based on perovskite thin layer, the surface morphology and roughness of the film becomes a crucial factor. A smoother surface will guarantee a better contact between the adjacent layers which in tun will reduce the contact resistance at the interface, and consequently, a more efficient charge transfer inside the device will be accomplished. This in turn can reduce recombination rates of charge carriers at the interfaces and improve overall the fill factor (FF) of the device and lead to higher power conversion efficiencies (PCEs). Therefore, atomic force microscopy (AFM) was used to evaluate the surface topology of perovskite thin layers deposited on top of glass / ITO substrates. The AFM image shown in Figure 2c signify grain sizes up to 1 pm in diameter and a low surface roughness value of 12.6 nm.138000GB1 - 28 - To assess the phase purity of the film, X-ray diffraction (XRD) was performed on the prepared MAPI sample. The XRD patterns and the corresponding the miller indices for the relative peaks are presented in Figure 3a. The results match the reported data in literature with the highest accuracy, showing all the expected peak values for the tetragonal black phase of MAPI perovskite (see Peng, H., et al., High-quality perovskite CH3NH3PbI3 thin films for solar cells prepared by single-source thermal evaporation combined with solvent treatment. Materials, 2019. 12(8): p. 1237). The observed intense diffraction peaks at 2-theta values of 14.12°, 28.44°, and 32°, are assigned to (110), (220), and (310) planes of the MAPI tetragonal phase, respectively, and suggest the high phase purity for the coated layer. However, the presence of multiple peaks suggest that the deposited thin film does not feature a preferred orientation. The diffraction peak appearing at 12.6° is characteristic to Pbh, which was present in the ink. Using a small amount of KSCN as additive inside the ink also led to the presence of scarce amount of KPb in the final film, represented by a weak peak at the 2-theta value of 9.5°.

[0181] Example 3 - Investigation of the electronic properties and charge dynamics of the perovskite film

[0182] To further investigate the electronic properties and the charge dynamics of the developed perovskite layer, steady state and time-resolved photoluminescence (PL and TRPL) measurements were conducted on the MAPI perovskite (bar coated NT ink) on bare ITO glass (sample A structure: Glass / ITO / MAPI) and on top of bar-coated SAM layer (sample B structure: Glass / ITO / SAM / MAPI). The self-assembled monolayer (SAM) used in this example was Me-4PACz.

[0183] Sample A structures were produced as described in Example 2. Sample B structures were fabricated starting with the precleaning of substrates, as described in Example 2. For a hole transport layer (HTL), a solution of SAM (1 mmol L-1in ethanol) was applied to the ITO substrates through bar coating process. The coating parameters included a 300 pm gap between the bar and substrate, a variable coating speed of 20 to 22 mm / s, an ink volume of 80 pL for 5 cm x 5 cm substrates. The coating was performed at room temperature. A 10 second delay was introduced before an intense gas blowing (with a pressure of 4 bar) step through N2 gun were performed on the centre area of the substrate, in a 2 to 3 cm height. The samples then annealed at 110°C for 10 minutes. All steps were performed in air. The MAPI layer was then coated inside a nitrogen-filled glovebox, using the non-toxic perovskite ink described in Table 2 and the method described in Example 2.138000GB1 - 29 - In the steady state photoluminescence spectra, the presence of a single peak at 778 nm with Gaussian shape indicates the expected band gap of approximately 1.58 eV for MAPI perovskite, suggesting no change in the perovskite crystal structure or phase purity when coated on top of SAM layer (Figure 3b). Moreover, a significant increase in PL intensity was observed for the MAPI film coated on SAM as hole transport layer (HTL). This might seem unexpected, as the affinity of the HTL towards holes would typically suppress radiative recombination when MAPI is coated on top of SAM, known as PL quenching. However, without wishing to be bound by theory, two possible reasons explain the higher PL intensity for sample B in comparison to sample A. First, the low interface quality between MAPI and ITO is well-known to enhanced non-radiative recombination at the interface, resulting in a substantial drop in the PL intensity for sample A. Second, the measurement was performed on the top side of the perovskite film, meaning the impact of HTL on the photo-generated holes is potentially less observable, depending on the thickness of the perovskite layer and the penetration depth of the laser beam (used for excitation).

[0184] To confirm this hypothesis, the inventors further measured the PL intensity for both samples while the excitement and measurement are done on the glass side (the buried side of the perovskite layer) (Figure 4). The results confirm a lower PL intensity, and an effective PL quenching for sample B compared to sample A. To better understand the charge collection ability of the SAM layer beneath the perovskite film, TRPL measurement was performed for both samples on the glass side (Figure 3c). Interestingly, the results show a higher decay time for the perovskite coated on top of HTL, with decay time of 2015 ns for sample B versus 554.6 ns for sample A (Table 3).

[0185] Table 3 - Fitted parameters of TRPL spectra for MAPbln perovskite films bar-coated on qlass / ITO and qlass / ITO / SAM substrates

[0186]

[0187] Further analysis of the decay curve reveals that the PL intensity drops more rapidly within the first 100 to 200 ns of the measurement timescale, for sample B, compared to sample A. However, this quickly transitions to a slower decay in the intensity for sample B after 250 to 300 ns. Studies indicate that the initial rapid drop in PL intensity is associated with the impact the adjacent charge-selecting layer in the sample structure (see Wolff, C.M., et al., Reduced interface-mediated recombination for high138000GB1 - 30 -open-circuit voltages in CH3NH3PbI3 solar cells. Advanced materials, 2017. 29(28): p.

[0188] 1700159 and He, R., et al., Scalable Preparation of High-Performance ZnO-SnCh Cascaded Electron Transport Layer for Efficient Perovskite Solar Modules. Solar RRL, 2022. 6(3): p. 2100639). The tendency of the HTL to attract generated holes causes an imbalance in charge distribution, leading to more non-radiative recombination within the film. However, the impact is short term, as the affinity of the HTL can quickly saturate by attracting holes in the absence of a complete circuit in the sample. Therefore, this effect only persists for the initial nanoseconds of the TRPL measurement. After this stage, the interface quality becomes the main factor in delaying the decay, by ensuring fewer charge recombination centres at the interface, resulting less non-radiative recombination. This leads to longer PL radiation time and extended decay time.

[0189] The obtained TRPL results support the PL data and further confirms the high quality of MAPI perovskite layer bar coated on top of SAM, compared to the one on bare ITO.

[0190] Example 4 - Perovskite mini module fabrication

[0191] Perovskite solar modules (PSMs) were fabricated, on glass substrates with p-i-n device structure of ITO / Me-4PACz / MAPI / C6o / BCP / Ag or ITO / MeO-4PACz / MAPI / C6o / BCP / Ag.

[0192] Initially, Glass / ITO / SAM / MAPI structures were fabricated using the method described in Example 3. Subsequent to the MAPI layer being coated, the samples were transferred to a vacuum deposition chamber for the thermal deposition of a 20 nm thick C60 layer and a 7 nm thick BCP layer, followed by thermal deposition of a 100 nm thick silver film as the top electrode. Laser scribing was employed to define the sub-cells and active area of the fabricated modules, consisting of four sub-cells connected in series. To achieve minimal dead area, four-step laser scribing (Pl to P4) was performed: Pl before precleaning on bare ITO substrate, P2 after coating all layers except the top electrode, P3 after depositing the top electrode, and P4 to completely isolate the active area.

[0193] The resultant devices contained four sub-cells which were monolithically connected in series to form a small mini module (MMS) with a total active area of 3.8 cm2and a geometrical fill factor (GFF) above 95%.

[0194] Example 5 - Perovskite mini module characterisation

[0195] X-ray diffraction (XRD) data for the samples were collected using a PANalytical X'Pert Pro powder diffractometer in Bragg-Brentano geometry with a Cu Ko source (45 kV,138000GB1 - 31 - 30 mA). Scanning Electron Microscope (SEM) images were captured with a Jeol JSM-7800F field emission gun electron microscope, set at a working distance of approximately 10 mm, an acceleration voltage of 5 kV, and a probe current around 8 pA. Atomic Force Microscopy (AFM) images were obtained using a Bruker Dimension Edge in tapping mode. Photoluminescence (PL) and time-resolved photoluminescence (TRPL) data were acquired with a Picoquant FluoTime 300 fluorescence spectrometer. The decay curves were modelled using a specific formula.

[0196]

[0197] J—V measurements of the perovskite solar modules (PSMs) were performed in Nz-filled glovebox at room temperature without encapsulation. Simulated sunlight was provided by an Enlitech SS-F5-3A solar simulator, delivering one-sun AM 1.5G illumination (100 mW cm-2). Light intensity was calibrated using a standard monocrystalline silicon solar cell with a KG-5 filter, and a reference cell from Fraunhofer ISE CalLab (ISE001 / 013-2018). All devices were measured using a Keysight B2901A source meter in both reverse (4.4 - -0.4 V, step 0.04 V, with 100 ns delay time) and forward (-0.4 - 4.4 V, step 0.04 V, with 100 ns delay time) scans. The active area was precisely defined through laser cutting around the PSM, ensuring an exact value of 3.8 cm2, eliminating the need for an aperture mask.

[0198] A photo of the fabricated PSM, along with an SEM cross-section image, are provided in Figure 5a and b, respectively. These images depict the module design, as well as the stack, thickness and quality of active layers inside the device.

[0199] The statistical box charts of the photovoltaic parameters for 20 PSMs is presented in Figure 5c. The JV curve for the champion device (i.e. the best performance device), and the corresponding performance parameter values are shown in Figure 5d, and Table 4, respectively. This shows the relatively high performance of the solar cell, and subsequently the high quality of the perovskite thin layer obtained from the non-toxic ink.

[0200] Table 4 - Performance parameters for the champion PSM device with the active area of 3.8 cm2

[0201]

[0202] 138000GB1 - 32 -

[0203]

[0204] The inventors further increased the module active area to 11.515 cm2in a design consisting of 7 sub-cells, connected in series. The well-optimized developed film fabrication process could successfully guarantee the highest quality for the film over most of the coating area on a 5x5 cm2substrate, allowing for an enhanced use of the coating area. The medium-sized mini module (MMM) devices showed even slightly higher performance, with an efficiency as high as 18.22%, Voc of 7.52 V, Jsc of 3.22 mA cm’2, and FF of 75.2% when the SAM was Me-4PACz (Table 5). The JV curve for the champion device, and the statistics for the photovoltaic parameters for 16 PSMs are presented in Figure 6a and b.

[0205] Table 5 - Performance parameters for the champion PSM devices

[0206]

[0207] Example 6 - Investigation of an alternative EtOH, 2MeTHF and DMSO composition The inventors then used the Hansen HSPiP program to identify further NT solvent systems. As noted above, the exemplified solvent system of 59 vol% EtOH, 39 vol% 2MeTHF and 2 vol% DMSO had HSP parameters of 3D: 16.1, 6P: 7.4 and 6H: 13.5. These values were used as target values.138000GB1 - 33 -

[0208] First, the inventors explored a range of mixing ratios between EtOH, MeTHF and DMSO, calculated their HSP parameters (provided in Table 7, below), and tested their ability to dissolve perovskite precursors. To test the developed non-toxic solvent system's ability to dissolve various perovskite precursors, they added the additives shown in Table 6 to the precursor mixture, all of which successfully dissolved. For EtOH (containing 33 wt% MA°) and 2MeTHF, the inventors found that combinations from 50 / 50 vol% to 70 / 30 vol% effectively dissolve MAPI perovskite precursors. This corresponds to weight ratios of EtOH:2MeTHF of 37:63 to 58:42.

[0209] Table 6 - Additives added to the precursor mixture

[0210]

[0211] The inventors made inks by adding the above additives to a solvent system consisting of 390 pL 2MeTHF, 590 pL EtOH containing 33 wt% methylamine MA° and 20 pL DMSO. Perovskite thin layers were bar coated, as described above. SEM images of the perovskite thin layers are presented in Figure 7a-c, corresponding to the inks comprising the additives from tests 1 to 3, respectively. A high-quality perovskite thin film should have grains attached next to each other without voids and pinholes between them to guarantee a smooth charge transfer within the film. Also, the relative small grains (a range of grain size are accepted from 100 nm to ~10 pm) can help the formation of a smooth surface for the film, leading to a mirror-like shiny perovskite layer. This can further help with the charge transfer between the perovskite and the neighbouring films. If the grains are too small, grain boundaries will cause high defect density inside the film, leading to lose the photo-generated charge, and if they are too big, they will impact the surface of the film and form a rough surface which is detrimental to the device performance.

[0212] The SEM images show the packed crystal grains inside the various perovskite thin films achieved from the different non-toxic solvent systems. These films have packed crystal grains with no void and pinhole. The crystal grains are an acceptable size (i.e. not too big or too small).138000GB1 - 34 -

[0213] Example 7 - Investigation of further NT perovskite ink solvent systems

[0214] The inventors then looked at using methanol (MeOH), 2-propanol (IPA), 1-butanol (BuOH), cyclopentyl methyl ether (CPME ) and / or ethyl acetate (EA) as additional or alternative solvents using the Hansen HSPiP program, and the results are provided in Table 7 below.

[0215] Based upon the calculated HSP parameters, the inventors then successfully prepared the inks shown in Table 7.

[0216] Table 7 - Hansen solubility parameters for further solvent systems tested

[0217]

[0218] 138000GB1 - 35 -

[0219]

[0220] Table 8 - New perovskite inks, using the solvent systems identified in Table 7

[0221]

[0222] 138000GB1 - 36 -

[0223]

[0224] * The EtOH used in the solvent systems identified in Tables 7 and 8 contained 33 wt% MA° and the MeOH was a solution of MeOH comprising 2.0 M of MA°. The volume ratio given in Tables 7 and 8 is based on the volume of EtOH or MeOH comprising MA°. The weight ratio given in Table 7 is of the weight of the pure solvents, and does not include MA°.

[0225] As shown in Table 8, the inventors developed new solvent systems by substituting MeTHF with EA, IPA or 1-BuOH. High-quality perovskite thin layers were achieved through bar coating these non-toxic inks (Figure 7d-f).

[0226] By replacing EtOH with MeOH while maintaining MeTHF in the solvent system, the inventors found that MeOH (containing 2M MA°) / MeTHF ratios from 50 / 50 vol% to 70 / 30 vol% could dissolve MAPI perovskite precursors. This corresponds to a weight ratio of the solvents of MeOH:MeTHF of 46:54 to 66:34. The resulting perovskite layers from MeOH-based inks were of a high quality (Figure 7g-h).

[0227] Furthermore, any double cation perovskite composition based on FA and MA (ranging from MAPI to pure FAPI (FAPbh) and any combination of FA and MA in between) can be readily dissolved in the proposed solvent system with slight adjustments to the solvent ratio. The inventors found that the optimized solvent system for FAMA-based perovskites comprises 20 vol% DMSO, 31 vol% 2MeTHF, and 49 vol% EtOH.

[0228] Perovskite layers were produced through bar coating of the developed inks with compositions MA0.3FA0.7Pbh and MA0.5FA0.5Pbh- SEM images (Figure 7i-j) revealed that138000GB1 - 37 -both films exhibited densely packed crystal grains, effectively preventing the formation of pinholes.

[0229] Example 8 - Investigation of still further NT perovskite ink solvent systems

[0230] The inventors also investigated if further additives should be used. They prepare the perovskite ink shown in Table 9.

[0231] Table 9 - Composition of perovskite ink

[0232]

[0233] The inventors note that they were able to dissolve the solid components identified in Table 9 in the solvent system to produce the ink. The inventors were then able to use the ink to make a high-quality thin film using the methods described above.

[0234] Example 9 - Confirming compatibility of the perovskite ink with alternative substrates The inventors wanted to confirm that the ink was compatible with substrates other than glass and glass / ITO. Accordingly, using the ink identified in Table 2, the inventors bar-coated a perovskite film on a PET / ITO substrate, using the method described above. As shown in Figure 8, a high quality perovskite film was obtained.

[0235] Conclusion

[0236] The inventors have developed a non-toxic solvent system for MAPbh-based perovskite inks, optimized for large-area thin film fabrication using scalable deposition techniques such as bar and slot-die coating. Their innovative solvent system, comprising ethanol (EtOH) and 2-methyltetra hydrofuran (2MeTHF), provides a high vapor pressure and low boiling point, which are crucial for scalable deposition methods that lack the rotational force of spin coating and require rapid solvent removal. This is critical to achieve the desired nucleation step. The addition of a small amount of dimethyl sulfoxide (DMSO) to the solvent system ensured controlled crystal growth during the drying process, promoting lateral growth and resulting in larger grains that fill gaps,138000GB1 - 38 -leading to a fully covered coating area. This final solvent system demonstrated excellent solubility for various perovskite precursors by forming coordination complexes between MA° molecules and perovskite material (through dative coordination bonds) and facilitated the formation of high-quality perovskite films. The resulting films exhibited high crystallinity, uniformity, and optoelectronic properties, confirmed through comprehensive characterization techniques including SEM, AFM, XRD, PL and TRPL.

[0237] The use of SAMs as HTLs further enhanced the performance of the PSMs, achieving PCEs as high as 18% on glass substrates. This approach not only eliminates the use of toxic solvents but also simplifies the fabrication process into a single, rapid, roomtemperature coating step, making it highly suitable for industrial applications.

[0238] The successful implementation of this non-toxic solvent system marks a significant step towards the commercialization of perovskite solar modules, offering a safer and more environmentally friendly alternative to traditional methods. This advancement opens new possibilities for the large-scale production of high-efficiency, low-cost perovskite solar panels, contributing to the global efforts in sustainable energy generation and carbon emission reduction.

Claims

138000GB1 - 39 - Claims1. A perovskite ink comprising:a solvent system comprising:a first solvent, the first solvent being one or more Ci-io alcohol, wherein the solvent system comprises the first solvent in an amount of at least 25 wt%; andone or more perovskite precursors;wherein the perovskite ink and the solvent system do not comprise a toxic solvent.

2. The perovskite ink of claim 1, wherein the solvent system further comprises a coordinating solvent, wherein the coordinating solvent is a Lewis base.

3. The perovskite ink of claim 2, wherein the coordinating solvent is dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), l,3-dimethyl-3,4,5,6-tetrahydro-2(lH)-pyrimidinone (DMPU) or a combination thereof.

4. The perovskite ink of claim 2 or claim 3, wherein the solvent system comprises the coordinating solvent in an amount of between 0.01 and 75 wt%, between 0.1 and 60 wt%, between 0.5 and 55 wt%, between 1 and 50 wt%, between 1.5 and 45 wt%, between 2 and 40 wt%, between 2.5 and 35 wt% or between 2.8 and 32 wt%.

5. The perovskite ink of any preceding claim, wherein the first solvent is methanol, ethanol or a combination thereof.

6. The perovskite ink of any preceding claim, wherein the solvent system further comprise a second solvent, the second solvent being selected from one or more C2-12 ether, one or more C2-12 ester, one or more C1-10 alcohol or a combination thereof.

7. The perovskite ink of claim 6, wherein the solvent system comprises the second solvent in an amount of at least 30 wt%.

8. The perovskite ink of claim 6 or 7, wherein the solvent system substantially consists of the first solvent, the second solvent and a coordinating solvent, wherein the coordinating solvent is a Lewis base.138000GB1 - 40 - 9. The perovskite ink of any one of claims 6 to 8, wherein the second solvent is selected from the group consisting of 2-methyltetrahydrofuran (2-MeTHF), ethyl acetate (EA), 2-propanol (IPA), 1-butanol (1-BuOH) and a combination thereof.

10. The perovskite ink of any one of claims 6 to 9, wherein the weight ratio of the first solvent to the second solvent is between 26:74 and 80:20, between 28:72 and 78:22, between 30:70 and 76:24, between 32:68 and 74:26, between 34:66 and 72:28 or between 35:65 and 70:30.

11. The perovskite ink of any preceding claim, wherein the one or more perovskite precursors comprises (i) an ammonium halide and / or an amidinium halide; and (ii) a lead halide.

12. The perovskite ink of any preceding claim, wherein the ink further comprises a coordinating compound, wherein the coordinating compound is a Lewis base.

13. The perovskite ink of claim 12, wherein the coordinating compound is an amine, optionally methyl amine.

14. The perovskite ink of claim 12 or claim 13, wherein he ink comprises the coordinating compound at a concentration of between 0.05 and 20 M, between 0.1 and 15 M, between 0.5 and 12.5 M, between 1 and 10 M or between 1.5 and 9 M.

15. The perovskite ink of any preceding claim, wherein the ink further comprises one or more additives, optionally wherein the one or more additives is potassium thiocyanate (KSCN), 2,2'-bipyridyl, methylammonium acetate (MAAc), methylammonium formate (MAFa), 1-adamantylamine and / or lead(II) thiocyanate (Pb(SCN)2).

16. Use of a solvent system in the manufacture of a perovskite film, the solvent system comprising:a first solvent, the first solvent being one or more Ci-io alcohol, wherein the solvent system comprises the first solvent in an amount of at least 25 wt%; and wherein the solvent system does not comprise a toxic solvent.

17. A method of forming a perovskite film on a substrate, the method comprising:depositing a layer of a perovskite ink on a substrate, wherein the perovskite ink is as defined in any one claims 1 to 15; and138000GB1 - 41 - subsequently at least partially removing the solvent system from the substrate, to thereby cause a perovskite film to form on the substrate.

18. The method of claim 17, wherein prior to depositing the layer of perovskite ink on the substrate, the method comprises cleaning the substrate.

19. The method of claim 17 or claim 18, wherein the method comprises depositing one of one or more hole-transporting layers (HTLs) and one or more electron transport layers (ETLs) prior to depositing the layer of the perovskite ink on the substrate and depositing the other of the one or more HTLs and one or more ETLs on the substrate subsequent to causing a perovskite film to form on the substrate.

20. The method of claim 19, wherein the method comprises:optionally cleaning the substrate;subsequently depositing the one or more HTLs on the substrate; subsequently depositing the layer of perovskite ink on the substrate; subsequently at least partially removing the solvent system from the substrate, to thereby cause a perovskite film to form on the substrate; andsubsequently depositing the one or more ETLs on the substrate.

21. The method of claim 19, wherein the method comprises:optionally cleaning the substrate;subsequently depositing the one or more ETLs on the substrate; subsequently depositing the layer of perovskite ink on the substrate; subsequently at least partially removing the solvent system from the substrate, to thereby cause a perovskite film to form on the substrate; andsubsequently depositing the one or more HTLs on the substrate.

22. The method of any one of claims 17 to 21, wherein depositing the layer of perovskite ink on the substrate comprises slot-die coating, bar coating or blade coating the layer of perovskite ink on the substrate.

23. The method of any one of claims 17 to 22, wherein partially removing the solvent system from the substrate comprises contacting the layer of perovskite ink on the substrate and a gas stream.138000GB1 - 42 - 24. The method of any one of claims 17 to 23, wherein the method comprises heating the substrate with the layer of perovskite ink thereon to an elevated temperature, and thereby annealing the perovskite film.

25. The method of any one of claims 17 to 24, wherein the method comprises depositing one or more electrode layers on the substrate.

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