利用赖氨酸掺杂优化PEDOT:PSS以提升倒置钙钛矿太阳能电池的性能

Enhancing the performance of inverted perovskite solar cells by optimizing PEDOT:PSS with lysine additive

聚[3,4-乙烯二氧噻吩]:聚苯乙烯磺酸盐(PEDOT:PSS)因其制备工艺简单、导电性能良好、成膜均匀及成本低廉等优势,已成为倒置型钙钛矿太阳能电池(perovskite solar cells,PSCs)中空穴传输层的首选材料.然而,由PSS链中的磺酸基团所导致的酸性和吸湿性等问题,对PSCs器件的光电性能和长期稳定性都造成了不良影响.针对以上问题,本文采用向PEDOT:PSS溶液中加入适量碱性赖氨酸的方法,利用赖氨酸中的氨基与PSS链中的磺酸基团的中和反应以适度调节PEDOT:PSS的酸性,改善了沉积于其上的钙钛矿薄膜的成膜质量,提高了器件的光电性能和长期稳定性.实验结果表明:使用赖氨酸掺杂的PEDOT:PSS薄膜为空穴传输层(hole transport layer,HTL)制备的倒置型PSCs器件,其开路电压(open circuit voltage,V_(OC))从0.94 V(未掺杂的PEDOT:PSS薄膜为HTL的参考器件)提升至1.04 V,短路电流(short circuit current,J_(SC))从20.81 mA cm^(-2)(参考器件)增加到21.35 mA cm^(-2),光电转换效率(power conversion efficiency,PCE)从15.71%(参考器件)提高到17.65%.此外,将未封装的赖氨酸掺杂的PSCs器件在氮气氛围(25℃)中存储2160 h后,其PCE保持为初始效率的86.54%;而在空气环境(25℃@15%相对湿度)中储存360 h后,其PCE仍能保持初始效率的85.88%.总的说来,将碱性赖氨酸作为掺杂剂引入PEDOT:PSS溶液,不仅能够适度中和PEDOT:PSS的酸性,还能改善钙钛矿薄膜的结晶性能和成膜质量,为实现高效稳定的倒置PSCs提供了一种新的思路.

Over the past few years, inverted perovskite solar cells (PSCs), whose architecture is anode/hole transport layer (HTL)/perovskite/electron transport layer/cathode, have exhibited a high potential for industrial application due to their lowpreparation temperature and cost-effective solution processing. To obtain high-performance inverted PSCs, it is crucial tochoose a suitable HTL material because it can affect the quality of the subsequently deposited perovskite absorbing layer.Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is regarded as one of the most attractive HTLmaterials for inverted PSCs due to its inherent merits of a simple preparation process, good conductivity, uniform filmformation, and low cost. However, the acidic property of the PEDOT:PSS solution and the strong hygroscopicity of thePEDOT:PSS film, which are caused by the sulfonic acid groups in the PSS chain, are detrimental to improving thephotovoltaic performance and long-term stability of inverted PSCs. Therefore, it is urgent to adjust the acidity of thePEDOT:PSS solution and optimize the quality of the PEDOT:PSS film to enhance the photovoltaic performance ofinverted PSCs based on PEDOT:PSS HTL.In this work, a simple and effective strategy, doping lysine additive into the PEDOT:PSS original solution, has beenproposed to adjust the acidity of the PEDOT:PSS solution and improve the film quality of the PEDOT:PSS film. By dopingan appropriate amount of lysine additive into the PEDOT:PSS original solution, the pH of the PEDOT:PSS solution wasadjusted from 3.5 (original PEDOT:PSS solution) to 7 (20 wt% lysine-doped PEDOT:PSS solution) due to theneutralization reaction between the amino groups in the lysine additive and the sulfonic acid groups in the PSS chain. Inaddition, the lysine additive could restructure the distribution of sulfonic acid groups and sulfonate groups within thePEDOT:PSS film, which is beneficial for reducing the roughness of the PEDOT:PSS film and thereby improving thequality of the subsequently deposited perovskite film with a relatively larger grain size. Furthermore, a better energy-levelmatching between the lysine-doped PEDOT:PSS layer and the perovskite layer is achieved, which is helpful for enhancinghole extraction from the perovskite layer to the lysine-doped PEDOT:PSS HTL. As a result, the open-circuit voltage (VOC)of the inverted PSCs based on lysine-doped PEDOT:PSS HTL increased from 0.94 V (reference device with undopedPEDOT:PSS film as HTL) to 1.04 V, the short-circuit current (J_(SC)) improved from 20.81 mA/cm^(2) (reference device) to21.35 mA/cm^(2), and the power conversion efficiency (PCE) rose from 15.71% (reference device) to 17.65%. In addition, thelysine-doped PSCs exhibit relatively high long-term stability due to the high quality of the perovskite film coated on thelysine-doped PEDOT:PSS HTL. The unencapsulated lysine-doped PSCs maintained 86.54% of its initial PCE value afterbeing stored in a nitrogen atmosphere (25℃) for 2160 hours, and kept over 85.88% of its initial PCE after being stored in anair environment (25℃, 15% RH) for 360 hours, respectively. Taking all above into account, introducing lysine as anadditive into PEDOT:PSS solution can not only moderately neutralize its acidity but also improve the crystallizationperformance and film quality of the perovskite film, providing a new strategy for achieving efficient and stable invertedPSCs.