Enhancing quality of CsPbIBr ₂ inorganic perovskite via cellulose acetate addition for high-performance perovskite solar cells

Wang Gui-Qiang , Bi Jia-Yu , Liu Jie-Qiong , Lei Miao , Zhang Wei 由于具有适合的带隙和较高的稳定性, CsPbIBr ₂ 无机钙钛矿被认为是一种较有前景的太阳能电池光吸收材料. 但是目前报道的CsPbIBr ₂ 钙钛矿太阳能电池效率还偏低, 主要原因是制备的CsPbIBr ₂ 钙钛矿膜质量差、缺陷多. 本文通过将醋酸纤维素(CA)加入CsPbIBr ₂ 钙钛矿前驱体溶液中改善CsPbIBr ₂ 钙钛矿结晶过程, 从而制备高质量的CsPbIBr ₂ 钙钛矿膜. 实验结果表明, CA中的C=O基团与前驱体溶液中的Pb ²⁺ 间存在明显的相互作用, 这种相互作用结合CA加入引起的前驱体溶液粘度增加, 使CsPbIBr ₂ 钙钛矿的结晶速率明显降低, 从而制备了致密、结晶度高、晶粒尺寸大、晶界和缺陷少的高质量CsPbIBr ₂ 钙钛矿膜. 同时, CA的保护作用显著提高了CsPbIBr ₂ 钙钛矿膜的稳定性. 用碳材料层作为空穴传输层和背电极, 制备结构为FTO/TiO ₂ /CsPbIBr ₂ 钙钛矿膜/碳层的碳基CsPbIBr ₂ 钙钛矿太阳能电池. 在100 mW/cm ² 光照下, CA-CsPbIBr ₂ 钙钛矿太阳能电池的效率达到7.52%, 比未加CA的CsPbIBr ₂ 钙钛矿电池提高了40%. 同时, 将CA-CsPbIBr ₂ 钙钛矿太阳能电池在空气环境中贮存800 h, 其效率仍保持初始值的90%以上, 表明具有较高的长期稳定性. 醋酸纤维素 /  CsPbIBr ₂ 钙钛矿 /  稳定性 /  钙钛矿太阳能电池 CsPbIBr ₂ perovskite has been considered as a promising candidate for the light-harvesting material of perovskite solar cells (PSCs) due to its acceptable band gap and high stability. Nevertheless, the efficiency of CsPbIBr ₂ -based PSC still lags behind that of its homologs and is far away from the theoretical value. This can be attributed to the poor quality of CsPbIBr ₂ perovskite film. Therefore, it is highly desirable to improve the quality of CsPbIBr ₂ perovskite film for enhancing the photovoltaic performance of CsPbIBr ₂ PSCs. In this work, cellulose acetate (CA) is used as a polymer additive that is introduced into CsPbIBr ₂ precursor solution for improving the quality of CsPbIBr ₂ perovskite film via controlling crystallization process. The interaction between the C=O group of CA and Pb ²⁺ in the precursor solution and the enhanced viscosity of precursor solution induced by CA addition reduce the crystallization rate of CsPbIBr ₂ perovskite. As a result, a compact CsPbIBr ₂ perovskite film with high crystallinity, large grain size, and low density of defect is prepared. The remarkably improved quality of CsPbIBr ₂ perovskite film upon CA addition can be attributed to the relatively slow crystallization rate. The slow crystallization rate allows the perovskite film to have enough time to form perfect perovskite crystal structure with large-size crystal grain and low density of defects. Furthermore, the oxygen functional groups of CA can passivate the undercoordinated Pb ²⁺ , which effectively suppresses the defects and traps induced by Pb ²⁺ in CsPbIBr ₂ perovskite film. The stability of CsPbIBr ₂ perovskite film is also greatly improved by CA addition. The added CA does not participate into the CsPbIBr ₂ perovskite crystal but distributes at the grain boundaries and, or, interfaces area and forms a moisture barrier around perovskite grains, which obviously enhances the stability of CsPbIBr ₂ perovskite film in the ambient air. The carbon-based CsPbIBr ₂ perovskite solar cells with a configuration of FTO/TiO ₂ /perovskite film/ carbon are fabricated by using the carbon layer as both the hole-transport layer and the back electrode. Under the illumination of 100 mW/cm ² , the PSC based on CA-CsPbIBr ₂ perovskite film delivers a high conversion efficiency of 7.52%, which is increased by 40% compared with the efficiency of the device based on the pure CsPbIBr ₂ perovskite film. In addition, the PSC based on CA-CsPbIBr ₂ perovskite film shows a hysteresis index (HI) of 7%, while the device based on pure CsPbIBr ₂ film displays a higher HI of 22%. This result demonstrates that the CA addition can effectively suppress the hysteresis effect of inorganic PSCs. The stability of the PSC based on CA-CsPbIBr ₂ perovskite film is investigated by tracking the variation of the efficiency with time in the ambient condition. The fabricated PSCs without any encapsulation are stored in the air. The photovoltaic performance is measured once a day. The efficiency of the PSC based on CA-CsPbIBr ₂ perovskite remains more than 90% of its initial value after being stored in the air for 800 h, showing an excellent long-term stability. Therefore, this work provides a facile and effective method of improving the quality of CsPbIBr ₂ perovskite films, which is expected to be helpful in developing high-efficiency and stable carbon-based inorganic PSCs. Keywords: cellulose acetate /  CsPbIBr ₂ perovskite /  stability /  perovskite solar cells Fig. 7 . (a) Photocurrent density-voltage ( J - V ) curves of perovskite solar cells based on CsPbIBr ₂ and CA-CsPbIBr ₂ perovskite films measured under forward and reverse scans; (b) Nyquist plots of CsPbIBr ₂ and CA-CsPbIBr ₂ perovskite solar cells; (c) variation of PCE of perovskite solar cells based on CsPbIBr ₂ and CA-CsPbIBr ₂ perovskite films stored in ambient air.

电池扫描方向 V _oc /V J _sc /(mA·cm ² )FFPCE/%HI ^a R _rec /Ω CsPbIBr ₂ 正向平均0.96 ± 0.059.89 ± 0.390.33 ± 0.43.13 ± 0.7222%1448最高1.0310.350.394.16反向平均1.01 ± 0.0310.21 ± 0.420.45 ± 0.024.64 ± 0.56最高1.0710.620.475.34CA
-CsPbIBr ₂ 正向平均1.02 ± 0.0310.52 ± 0.370.57 ± 0.026.12 ± 0.677%2269最高1.0610.910.606.94反向平均1.05 ± 0.0310.55 ± 0.270.62 ± 0.026.87 ± 0.38最高1.0810.880.647.52 ^a HI = (PCE _反向 –PCE _正向 )/PCE _反向 王辉, 郑德旭, 姜箫, 曹越先, 杜敏永, 王开, 刘生忠, 张春福. 基于协同钝化策略制备高性能柔性钙钛矿太阳能电池 . 物理学报, 2024, 73(7): 078401. doi: 10.7498/aps.73.20231846 羊美丽, 邹丽, 程佳杰, 王佳明, 江钰帆, 郝会颖, 邢杰, 刘昊, 樊振军, 董敬敬. 聚偏氟乙烯添加剂提高CsPbBr ₃ 钙钛矿太阳能电池性能 . 物理学报, 2023, 72(16): 168101. doi: 10.7498/aps.72.20230636 杨迎国, 阴广志, 冯尚蕾, 李萌, 季庚午, 宋飞, 文闻, 高兴宇. 湿度环境下钙钛矿太阳能电池薄膜微结构演化的同步辐射原位实时研究 . 物理学报, 2017, 66(1): 018401. doi: 10.7498/aps.66.018401 石将建, 卫会云, 朱立峰, 许信, 徐余颛, 吕松涛, 吴会觉, 罗艳红, 李冬梅, 孟庆波. 钙钛矿太阳能电池中S形伏安特性研究 . 物理学报, 2015, 64(3): 038402. doi: 10.7498/aps.64.038402