Hole transport materials containing cyanophosphate units, their preparation methods and applications

Abstract

This invention relates to a type of hole transport material containing cyanophosphate units, its preparation method, and its application, having the structures shown in formulas (I) to (IV): where R is hydrogen, alkyl, alkoxy, alkylthio, or phenyl. The hole transport material containing cyanophosphate units of this invention can be used in the hole transport layer of perovskite solar cells. Compared to the organic hole transport layers of existing p-i-n type perovskite solar cells, this type of hole transport layer has advantages such as good stability, ease of processing, absence of dopants, and low cost. Furthermore, its excellent charge selectivity enables the acquisition of highly efficient and stable perovskite solar cell devices.

Description

Technical Field

[0001] This invention belongs to the field of energy materials, specifically relating to a type of hole transport material containing cyanophosphate units, its preparation method, and its applications. Background Technology

[0002] Energy is the most fundamental driving force for global scientific and technological development and economic growth, and the foundation upon which humanity depends for survival and development. Since the beginning of the 21st century, energy issues have gradually intensified. It is well known that fossil fuels are currently the most consumed energy source globally, but with continuous human exploitation, the depletion of fossil fuels is inevitable, and most fossil fuels will be exhausted within this century. Solar energy is a renewable energy source with broad application prospects. Solar cells can directly convert solar radiation into electrical energy without polluting the environment, making them an ideal way to obtain solar energy. Perovskite solar cells are considered the best alternative to silicon solar cells due to their ease of fabrication, low cost, and excellent photoelectric performance.

[0003] Compared to nip-type perovskite solar cells, pin-type perovskite solar cells demonstrate great potential for future commercialization due to their superior long-term operational stability, low-temperature fabrication capability, and low hysteresis. The hole transport layer plays a crucial role in this process, and the use of small organic molecules with anchoring groups to prepare hole transport layers has proven to exhibit excellent charge selectivity (Energy Environ. Sci., 2019, 12, 230-237). However, currently developed small organic molecule hole transport materials with anchoring groups face challenges such as poor stability and unsatisfactory device performance. Therefore, the design and development of novel small organic molecule hole transport materials with anchoring groups are essential for achieving efficient and stable perovskite solar cell devices. Summary of the Invention

[0004] The primary objective of this invention is to provide a type of hole transport material for pin-type perovskite solar cells.

[0005] A class of hole transport materials containing cyanophosphate units have the structures shown in formulas (I) to (IV):

[0006]

[0007]

[0008] In the formula: R is hydrogen, alkyl, alkoxy, alkylthio, or phenyl.

[0009] Another objective of this invention is to provide a method for preparing the aforementioned hole transport material;

[0010] The synthesis steps are as follows:

[0011]

[0012] The main steps of the method are as follows: using substituted 4-diphenylaminobenzaldehyde (V) as the starting material, the corresponding phosphate ester (VI) is generated by Knoevenagel condensation reaction with diethyl cyanomethyl phosphate, and then further reacted with trimethylbromosilane to undergo deesterification to obtain the compound shown in formula (I).

[0013] Another objective of this invention is to provide an application of the aforementioned hole transport material, specifically the application of cyanophosphate-containing hole transport materials in the hole transport layer of perovskite solar cells. Compared to the organic hole transport layers of existing pin-type perovskite solar cells, this type of hole transport layer offers advantages such as good stability, ease of processing, absence of dopants, and low cost. Furthermore, its excellent charge selectivity enables the acquisition of highly efficient and stable perovskite solar cell devices. Attached Figure Description

[0014] Figure 1 The cyclic voltammetry curve of the compound shown in formula (I) in dichloromethane solution (supporting electrolyte is 0.1 M tetrabutylammonium hexafluorophosphate);

[0015] Figure 2 The diagram shows the contact angle change of ITO after spin coating (I) with hole transport material.

[0016] Figure 3 The image shows the C1s signal of XPS on ITO after spin coating of hole transport material as shown in (I).

[0017] Figure 4 The image shows the fluorescence lifetime of the perovskite film after spin-coating the hole transport material shown in (I).

[0018] Figure 5 The JV curves are shown for perovskite solar cells using the compound shown in formula (I) and the commercially available compound MeO-2PACz as hole transport materials.

[0019] Figure 6 It is the nuclear magnetic resonance spectrum of step (1) in Example 1.

[0020] Figure 7 It is the nuclear magnetic resonance spectrum of step (2) in Example 1.

[0021] Figure 8 It is the nuclear magnetic resonance spectrum of step (1) in Example 2.

[0022] Figure 9 It is the nuclear magnetic resonance spectrum of step (2) in Example 2. Detailed Implementation

[0023] A method for preparing the self-assembled hole transport material and hydrophilic molecules described in this invention comprises the following steps:

[0024] a) Using formula (V) and diethyl cyanomethyl phosphate as raw materials, the intermediate shown in formula (VI) is obtained by Knoevenagel condensation reaction;

[0025] b) The intermediate formula (VI) was placed in an ultra-dry dichloromethane solution, and trimethylbromosilane was added dropwise. After reacting for 8 hours, methanol was added to directly obtain the hole transport material with cyanophosphate acceptor shown in formula (I).

[0026] The hole transport material containing cyanophosphate units [compounds shown in formulas (I-IV)] described in this invention can be used as a hole transport layer in perovskite solar cells. This type of hole transport material exhibits good electrochemical stability and charge extraction capability. The cyclic voltammetric characteristics and hole extraction capability of this type of hole transport material to the perovskite layer were characterized, and the results are shown in the appendix. Figures 1-5 As shown, the perovskite solar cell comprises: a stacked structure with conductive ITO or FTO glass as the photocathode, organic small molecules with cyanophosphate groups as the hole transport layer, organic-inorganic hybrid perovskite as the photoactive layer, PCBM or C60 as the electron transport layer, BCP as the hole blocking layer, and metals such as gold or silver as the counter electrode.

[0027] The present invention will be further illustrated below through examples, with the aim of providing a better understanding of its content. Therefore, the examples given do not limit the scope of protection of the present invention.

[0028] Example 1

[0029]

[0030] (1) In a 50 mL round-bottom flask, 1 (500 mg, 1.83 mmol), 2 (800 μL, 4.9 mmol), toluene (20 mL), and piperidine (0.5 mL) were added sequentially. Under argon protection, the mixture was heated to 110 °C in an oil bath and refluxed for 10 h. The reaction was quenched by slowly adding water (10 mL), and extracted with dichloromethane (100 mL). The mixture was separated, and the organic phase was collected and dried over anhydrous sodium sulfate. After removing the dichloromethane by rotary evaporation under reduced pressure, the mixture was separated by column chromatography (dichloromethane:methanol = 10:1) to obtain an orange-yellow solid 3 (450 mg, 57.8%).

[0031] like Figure 6As shown, 1H NMR (400MHz, CDCl3, δ, ppm): 7.82-7.80 (m, 3H), 7.36-7.32 (m, 4H), 7.19-7.16 (m, 6H), 6.98 (d, J = 8.5Hz, 2H), 4.20 (m, 4H), 1.49 (t, 6H).

[0032]

[0033] (2) In a 100 mL round-bottom flask, add 3 (300 mg, 0.7 mmol) and ultra-dry dichloromethane (20 mL) in sequence. Under argon protection, add trimethylbromosilane (0.3 mL, 2.2 mmol) dropwise. After stirring at room temperature for 8 hours, evaporate to dryness. Then add 20 mL of methanol, stir at room temperature for 4 hours, and evaporate to dryness to obtain the final product (4).

[0034] like Figure 7 As shown, 1H NMR (400MHz, CDCl3, δ, ppm): 7.75-7.71 (m, 3H), 7.32-7.28 (m, 4H), 7.15-7.10 (m, 6H), 6.90 (d, J = 8.5Hz, 2H).

[0035] Example 2

[0036]

[0037] (1) In a 50 mL round-bottom flask, 5 (660 mg, 2.0 mmol), 2 (1000 μL, 6.1 mmol), toluene (20 mL), and piperidine (0.5 mL) were added sequentially. Under argon protection, the mixture was heated to 110 °C in an oil bath and refluxed for 10 h. The reaction was quenched by slowly adding water (10 mL), and extracted with dichloromethane (100 mL). The mixture was separated, and the organic phase was collected and dried over anhydrous sodium sulfate. After removing the dichloromethane by rotary evaporation under reduced pressure, the mixture was separated by column chromatography (dichloromethane:methanol = 10:1) to obtain a yellow solid 6 (500 mg, 51.0%).

[0038] like Figure 8 As shown, 1H NMR (400MHz, CDCl3, δ, ppm): 8.19 (d, J = 8.6Hz, 2H), 8.07 (d, J = 21.2 Hz,1H),7.73(d,J=8.6Hz,2H),7.54(d,J=2.5Hz,2H),7.45(d,J=8.9Hz,2H),7.05(dd,J1= 8.9Hz, J2=2.5Hz,2H),4.29(m,4H),3.96(s,6H),1.44(t,6H).

[0039]

[0040] (2) In a 100 mL round-bottom flask, add 3 (400 mg, 0.8 mmol) and ultra-dry dichloromethane (20 mL) in sequence. Under argon protection, add trimethylbromosilane (0.35 mL, 2.6 mmol) dropwise. After stirring at room temperature for 8 hours, evaporate to dryness. Then add 20 mL of methanol and stir at room temperature for 4 hours before evaporating to dryness to obtain the final product (7).

[0041] like Figure 9 As shown, 1H NMR (400MHz, DMSO-d6, ppm): 8.22 (d, J = 8.6Hz, 2H), 7.96 (d, J = 21.2 Hz,1H),7.84-7.81(m,4H),7.47(d,J=8.9Hz,2H),7.04(dd,J1=8.9Hz,J2=2.5Hz,2H), 3.88(s,6H).

[0042] Other molecules can be obtained by following similar steps, which will not be elaborated here.

[0043] Example 3

[0044] Fabricating perovskite solar cell devices using compounds shown in formulas (I-IV) as hole transport materials includes the following steps:

[0045] A) Preparation of the hole transport layer: A hole transport material solution (1 mmol / L) was prepared using ultradry ethanol. -1 Spin-coat the solution onto a clean ITO surface, anneal at 100°C for 10 minutes, and cool to room temperature before use;

[0046] B) Preparation of the perovskite layer: PbI₂, MABr, PbBr₂, FAI, and CsI were dissolved in a mixed solution of DMF:DMSO = 4:1 (1.5M) to form a perovskite layer with the chemical formula Cs. 0.05 (MA 0.05 FA 0.95 ) 0.95 Pb(Br 0.05 I 0.95 )3 Perovskite precursor solution, stirred at 50°C for 12 hours, and then a perovskite film was deposited on the hole transport layer by a "one-step method" using chlorobenzene as the antisolvent.

[0047] C) Preparation of electron transport layer and hole blocking layer: A solution of [6,6]-phenyl-C61-butyricacid methyl ester (PCBM) (20 mg mL-1) was prepared using chlorobenzene and stirred overnight at 50 °C. This solution was then spin-coated onto the perovskite layer. The hole blocking layer was obtained by spin-coating a saturated solution of copper oxychloride (BCP).

[0048] D) A 100 nm layer of silver was vacuum-deposited onto the hole-blocking layer as the counter electrode. This perovskite solar cell was then placed under simulated sunlight at AM1.5 and its current density-voltage curve was measured (using a Keithley 2400 digital source meter (Keithley, USA)). The cell's open-circuit voltage was 1.185 V, and the short-circuit current was 24.44 mA cm⁻¹. -2 The fill factor is 0.80, the photoelectric conversion efficiency is 23.3%, and its JV is shown in [reference needed]. Figure 5 The device exhibits significantly higher performance than commercially available hole transport material MeO-2PACz, with an open-circuit voltage of 1.148V and a short-circuit current of 24.04mA. -2 The fill factor is 0.73, and the photoelectric conversion efficiency is 20.3%.

Claims

1. The application of a type of hole transport material containing cyanophosphate units in the fabrication of perovskite solar cells, characterized in that, The hole transport material structure containing the cyanophosphate unit is shown below: The perovskite solar cell comprises: a conductive indium tin oxide or fluorine-doped tin oxide glass as a photocathode, a hole transport material containing cyanophosphate units as a hole transport layer, an organic-inorganic hybrid perovskite as a photoactive layer, [6,6]-phenyl-C61-butyrate methyl ester as an electron transport layer, and copper bath as a hole blocking layer.

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