Layered organic solar cells based on bithiazole additives and methods of making the same

Abstract

This invention belongs to the field of organic solar cell technology, and particularly relates to a layered organic solar cell based on a bithiazole additive and its fabrication method. The active layer of this cell includes a D18 donor layer and an acceptor layer containing L8-BO and a bithiazole additive (DBB), wherein the additive is only present in the acceptor layer. A layer-by-layer spin-coating process is employed, and the morphology of the acceptor layer is controlled by solid-state additives to solve the solvent residue problem. This achieves synergistic optimization of the exciton dissociation interface and charge transport channels, resulting in a photoelectric conversion efficiency of 19.7% and significantly improved stability.

Description

Technical Field

[0001] This invention belongs to the field of organic solar cell technology, and particularly relates to a layered organic solar cell based on bis(thiazole) additive and its preparation method. Background Technology

[0002] Organic solar cells (OSCs) have become a research hotspot in the photovoltaic field due to their advantages such as light weight, flexibility, solution-processability, and low cost. Among them, non-fullerene organic solar cells (NF-OSCs) have achieved a significant improvement in photoelectric conversion efficiency by matching narrow bandgap small molecule acceptor materials (such as L8-BO) with wide bandgap polymer donor materials (such as D18).

[0003] In organic solar cells, the active layer is the core functional layer for photogenerated exciton dissociation, carrier transport, and collection, and its microstructure directly determines the device performance. Currently, methods for controlling the active layer morphology mainly include thermal annealing, solvent additive engineering, and third-component doping. However, traditional bulk heterojunction (BHJ) devices employ a donor-acceptor co-spray coating process, resulting in a disordered component distribution. This makes it difficult to form an ideal vertical phase separation structure, leading to discontinuous charge transport channels and severe bimolecular recombination, thus limiting further improvements in photoelectric conversion efficiency.

[0004] Furthermore, while solvent-based additives (such as 1-chloronaphthalene, CN) can optimize film crystallinity, their residues in the active layer are difficult to completely remove. Residual solvents continuously alter the film morphology, accelerate the photo-oxidative degradation of the active layer, and reduce the long-term stability of the device.

[0005] Layer-by-layer (LbL) spin coating, by sequentially depositing donor and acceptor layers, can utilize solvent-induced limited diffusion to create a vertical concentration gradient, thus constructing a PIN structure conducive to exciton dissociation and charge transport. However, how to further control the morphology of the acceptor layer and suppress carrier recombination remains a pressing technical problem to be solved. Summary of the Invention

[0006] To address the aforementioned issues, the first technical solution of this application discloses an organic solar cell, comprising an anode, a hole transport layer, an active layer, an electron transport layer, and a cathode. The active layer comprises: a donor layer containing a polymer donor material D18; and an acceptor layer containing a non-fullerene acceptor material L8-BO and an additive having a bithiazole structure, wherein the additive exists only in the acceptor layer. The donor layer and the acceptor layer are formed sequentially via a layer-by-layer spin-coating process.

[0007] Preferably, the additive is 5,5'-dibromo-2,2'-bithiazole.

[0008] Preferably, the donor layer is formed by spin coating of D18 solution at a spin coating speed of 2000-3000 rpm.

[0009] Preferably, the receptor layer is formed by spin coating of a solution containing L8-BO and the additive at a spin coating speed of 3500-4500 rpm.

[0010] Preferably, the mass ratio of the additive to L8-BO is (0.5-2):100.

[0011] The second technical solution of this application discloses a method for preparing the organic solar cell described in the first technical solution, including:

[0012] Provide ITO substrate;

[0013] A hole transport layer is formed on the ITO substrate;

[0014] A donor layer is first spin-coated with a D18 solution onto the hole transport layer, and then a acceptor layer is formed by spin-coating with a solution containing L8-BO and the additive. The donor layer and the acceptor layer together constitute the active layer.

[0015] Forming an electron transport layer;

[0016] Ag electrode deposition.

[0017] Preferably, the solvent of the D18 solution is chlorobenzene, and the solvent of the solution containing L8-BO and additives is chloroform.

[0018] Preferably, the concentration of the D18 solution is 5-6 mg / mL, and the concentration of L8-BO in the solution containing L8-BO and additives is 6-8 mg / mL.

[0019] Preferably, the additive is added at a mass ratio of 0.5% to 2% relative to L8-BO.

[0020] The third technical solution of this application discloses the application of the organic solar cell described in the first technical solution in photoelectric conversion devices; wherein, the organic solar cell can be applied to photoelectric conversion devices, including but not limited to flexible solar cells, semi-transparent photovoltaic windows, power supply modules for wearable electronic devices, etc.

[0021] Beneficial effects:

[0022] (1) Significantly improves the vertical phase distribution of the active layer and enhances the photoelectric conversion efficiency.

[0023] This invention employs the LbL process to sequentially spin-coat a D18 donor layer and an L8-BO acceptor layer, forming a clearly defined vertically layered structure. Combined with the introduction of a bithiazole-based solid additive, 5,5'-dibromo-2,2'-bithiazole (DBB), only in the acceptor layer, the ordered stacking of acceptor molecules is induced through non-covalent interactions, constructing an optimized exciton dissociation interface and continuous charge transport channels. The device achieves a photoelectric conversion efficiency (PCE) of 19.7%, significantly higher than that of conventional BHJ structure devices.

[0024] (2) Avoid solvent additive residues and improve morphological stability

[0025] This invention uses solid additive DBB to replace traditional liquid solvent additives, fundamentally solving the problem of continuous evolution of film morphology and decreased stability caused by solvent residue. The solid additive participates in the crystallization regulation of the acceptor layer through intermolecular non-covalent interactions, and remains stably present in the active layer after film formation, without causing subsequent morphology degradation.

[0026] (3) Collaborative optimization of carrier transport performance

[0027] By selectively introducing DBB into the acceptor layer, the surface roughness of the thin film is reduced, the carrier trap density is decreased, bimolecular recombination is suppressed, the device fill factor (FF) is increased to over 77%, and the short-circuit current density (Jsc) is significantly increased, achieving synergistic optimization of open-circuit voltage, short-circuit current, and fill factor.

[0028] (4) It has strong process compatibility and is suitable for large-scale preparation.

[0029] The layer-by-layer spin coating process of this invention is fully compatible with solution processing technology, with controllable process parameters and good repeatability, providing a feasible technical solution for the large-area fabrication of high-performance organic solar cells. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a structural diagram of the organic solar cell device of this application;

[0032] Figure 2 This is a molecular structure diagram of D18, L8-BO, and DBB involved in this application;

[0033] Figure 3This is a flowchart of the organic solar cell fabrication process described in this application;

[0034] Figure 4 This is the theoretical calculation process for the amount of DBB added in this application; where (a) is the electrostatic potential distribution of the DBB additive; (b) is the optimal geometry between the additive DBB and L8-BO; and (c) is the RDG analysis of the L8-BO:DBB dimer.

[0035] Figure 5 The JV curve of the organic solar cell of this application;

[0036] Figure 6 This is an AFM characterization diagram of the organic solar cell of this application. Detailed Implementation

[0037] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0038] like Figure 1 As shown, the first embodiment of this application discloses an organic solar cell, the structure of which, from bottom to top, consists of an ITO conductive substrate, a PEDOT:PSS hole transport layer, an active layer, a PDIN electron transport layer, and an Ag electrode. The active layer is the core improvement of this invention, formed using a layer-by-layer (LbL) spin-coating process, and specifically includes two substructures: a donor layer and an acceptor layer.

[0039] like Figure 1 As shown, the donor layer is directly deposited on top of the PEDOT:PSS hole transport layer and contains the polymer donor material D18. Figure 2 As shown, D18 is a wide-bandgap polymer donor material (LUMO=-5.25 eV, HOMO=-2.88 eV). Its molecular structure contains conjugated backbone and side chain substituents, which are beneficial for light absorption and hole transport.

[0040] The donor layer is prepared by spin-coating a solution of D18 dissolved in chlorobenzene (CB). The spin-coating speed is controlled within the range of 2000-3000 rpm, preferably 2500 rpm. This speed range ensures the formation of a donor film of suitable thickness and with a smooth surface, guaranteeing sufficient light absorption and providing a good interface for the subsequent deposition of the acceptor layer.

[0041] like Figure 1As shown, the acceptor layer is deposited on top of the donor layer and comprises the non-fullerene acceptor material L8-BO and a solid additive with a bithiazole structure. The additive is present only in the acceptor layer and is absent from the donor layer; this spatial distribution characteristic is achieved through a layer-by-layer spin-coating process.

[0042] Specifically, the additive is 5,5'-dibromo-2,2'-bisthiazole (DBB), whose molecular structure is as follows: Figure 2 As shown, the DBB molecule contains a thiazo[5,4-d]thiazolyl core and a bromine substituent at the 5,5' position. These structural features endow it with the ability to form non-covalent interactions with L8-BO.

[0043] The acceptor layer was prepared by spin-coating a solution of L8-BO and DBB dissolved in chloroform (CF). The spin-coating speed was controlled within the range of 3500-4500 rpm, preferably 4000 rpm. This speed is higher than that of the donor layer spin-coating speed, which is beneficial for forming a thinner and denser acceptor layer and promoting efficient charge collection.

[0044] The mass ratio of the additive DBB to L8-BO is (0.5-2):100, preferably 1:100. This ratio range was determined through experimental optimization: when the ratio is below 0.5%, the additive has no significant effect on morphology regulation; when the ratio is above 2%, excessive additive may disrupt the orderly stacking of acceptor molecules, thereby reducing device performance.

[0045] like Figure 4 As shown, by observing the electrostatic potential (ESP) distribution of the additive material, it can be found that it exhibits a negative ESP distribution due to the presence of halogen elements. The electron-deficient core region of L8-BO and the negatively charged region of the additive have a perfect spatial match, easily forming intermolecular interactions. Furthermore, the intermolecular binding energy (ΔE) between the additive (DBB) and L8-BO was calculated using density functional theory (DFT). The additive tends to aggregate near the BTP units of L8-BO, and its optimal geometry is shown in the figure. Figure 4 As shown in (b). The density gradient distribution function (RDG) of the optimal molecular configuration was further determined. Figure 4 (c)). The blue and green areas represent strong and weak intermolecular forces, respectively. It can be seen that the introduction of the additive DBB can enhance the non-covalent attraction between molecules and promote the accumulation of acceptors.

[0046] The donor layer and acceptor layer are formed sequentially via a layer-by-layer spin-coating process. For example... Figure 3 As shown, a D18 solution is first spin-coated to form a solid donor layer. After the solvent evaporates, a solution containing L8-BO and DBB is then spin-coated to form an acceptor layer. This LbL structure differs from the traditional BHJ blend structure, as it can create a vertical concentration gradient that is conducive to charge transport. Figure 3 The specific preparation method of the organic solar cell of this application is disclosed.

[0047] 1. Substrate preparation and hole transport layer fabrication

[0048] ITO conductive glass was selected as the substrate and ultrasonically cleaned for 30 minutes each in water, ethanol, acetone and ethanol in sequence. After being dried with nitrogen, it was treated with ultraviolet ozone for 15 minutes to remove surface contaminants and improve surface energy.

[0049] The PEDOT:PSS solution was spin-coated at 4000 rpm for 30 seconds to form a uniform film, which was then heat-annealed at 150°C in air for 15 minutes to form a dense hole transport layer with a thickness of about 40 nm.

[0050] 2. Spin-coating the active layer layer by layer

[0051] Donor layer preparation: D18 is dissolved in chlorobenzene (CB) solvent at a concentration of 5-6 mg / mL, preferably 5.5 mg / mL. This concentration range ensures that the solution has a suitable viscosity, forming a uniform film with a thickness of approximately 100-120 nm at a spin coating speed of 2000-3000 rpm.

[0052] Receptor layer preparation: DBB additive is added to the L8-BO receptor to a mass ratio of 0.5%-2%, preferably 1% (i.e., mass ratio 1:100). Chloroform (boiling point 61°C) is used as the receptor layer solvent, with a concentration controlled at 6-8 mg / mL, preferably 7 mg / mL. The prepared solution is spin-coated at 3500-4500 rpm for 30 seconds to form the receptor layer.

[0053] 3. Electron transport layer and electrode fabrication

[0054] PDIN was dissolved in methanol (containing 0.3% acetic acid) at a concentration of 2 mg / mL, and spin-coated at 5000 rpm for 30 seconds to form an electron transport layer with a thickness of approximately 10 nm. Finally, the layer was coated under a vacuum of 5 × 10⁻⁻⁻⁻⁶. 4 Under Pa conditions, a 100 nm thick Ag electrode was thermally deposited to complete the device fabrication.

[0055] The technical solutions and effects of this application will be described in detail below with reference to specific embodiments.

[0056] Example 1

[0057] D18 / L8-BO:DBB layered devices were fabricated according to the above preparation method.

[0058] Donor solution: D18 dissolved in CB, concentration 5.5 mg / mL, spin coating speed 2500 rpm;

[0059] Receptor solution: L8-BO dissolved in CF at a concentration of 7 mg / mL, DBB to L8-BO mass ratio of 1:100 (i.e. 1% mass ratio), spin coating speed of 4000 rpm.

[0060] Device performance testing: such as Figure 5 As shown, the device has an open-circuit voltage (Voc) of 0.93 V, a short-circuit current density (Jsc) of 27.29 mA / cm², a fill factor (FF) of 77.73%, and a photoelectric conversion efficiency (PCE) of 19.7%. Figure 6 As shown, the surface morphology of the active layer is smooth and the roughness is low.

[0061] Comparative Example 1

[0062] DBB was not added to the receptor solution, and other conditions were the same as in Example 1. Figure 5 As shown, the device has a Voc of 0.93 V, Jsc of 26.35 mA / cm², fill factor (FF) of 75.89%, and PCE of 18.5%. In comparison, Example 1 achieves the technical effect of increasing the short-circuit current density (Jsc) from 26.35 mA / cm² to 27.29 mA / cm² and the fill factor (FF) from 75.89% to 77.73%. Figure 6 As shown, the surface roughness of Comparative Example 1 is significantly higher than that of Example 1, proving that the technical solution of Example 1 can optimize the morphology of the active layer and reduce carrier traps.

[0063] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. An organic solar cell, comprising an anode, a hole transport layer, an active layer, an electron transport layer, and a cathode, characterized in that, The active layer comprises: a donor layer containing polymer donor material D18; and an acceptor layer containing non-fullerene acceptor material L8-BO and an additive having a bithiazole structure, wherein the additive is present only in the acceptor layer; wherein the donor layer and the acceptor layer are formed sequentially by a layer-by-layer spin coating process.

2. The organic solar cell according to claim 1, characterized in that, The additive is 5,5'-dibromo-2,2'-bithiazole.

3. The organic solar cell according to claim 1, characterized in that, The donor layer is formed by spin coating of D18 solution at a spin coating speed of 2000-3000 rpm.

4. The organic solar cell according to claim 1, characterized in that, The receptor layer is formed by spin coating of a solution containing L8-BO and the additive at a spin coating speed of 3500-4500 rpm.

5. The organic solar cell according to claim 1, characterized in that, The mass ratio of the additive to L8-BO is (0.5-2):

100.

6. A method for preparing an organic solar cell as described in any one of claims 1-5, characterized in that, include: Provide ITO substrate; A hole transport layer is formed on the ITO substrate; A donor layer is first spin-coated with a D18 solution onto the hole transport layer, and then a acceptor layer is formed by spin-coating with a solution containing L8-BO and the additive. The donor layer and the acceptor layer together constitute the active layer. Forming an electron transport layer; Ag electrode deposition.

7. The preparation method according to claim 6, characterized in that, The solvent for the D18 solution is chlorobenzene, and the solvent for the solution containing L8-BO and additives is chloroform.

8. The preparation method according to claim 6, characterized in that, The concentration of the D18 solution is 5-6 mg / mL, and the concentration of L8-BO in the solution containing L8-BO and additives is 6-8 mg / mL.

9. The preparation method according to claim 6, characterized in that, The additive is added at a mass ratio of 0.5% to 2% relative to L8-BO.

10. The application of the organic solar cell according to any one of claims 1-5 in a photoelectric conversion device.

Images