Zwitterion Coordination Induced Highly Orientational Order of CH3NH3PbI3 Perovskite Film Delivers a High Open Circuit Voltage Exceeding 1.2 V

• Published in: Advanced functional materials Vol. 29; no. 23
• Main Authors: Zhou, Weiran, Li, Dan, Xiao, Zhengguo, Wen, Zhilin, Zhang, Mengmeng, Hu, Wanpei, Wu, Xiaojun, Wang, Mingtai, Zhang, Wen‐Hua, Lu, Yalin, Yang, Shihe, Yang, Shangfeng
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 06.06.2019
• Subjects: additive engineering; Coordination; Crystal structure; crystalline grain orientation; Doping; Electron transport; Energy conversion efficiency; Heterojunctions; Imidazole; Materials science; Open circuit voltage; perovskite solar cells; Perovskites; Photovoltaic cells; Solar cells; Titanium dioxide; trap passivation; zwitterion; Zwitterions
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201901026

The organic–inorganic halide CH3NH3PbI3 (MAPbI3) has been the most commonly used light absorber layer of perovskite solar cells (PSCs); however, solution‐processed MAPbI3 films usually suffer from random crystal orientation and high trap density, resulting in inferior power conversion efficiency (PCE) with open circuit voltage (Voc) being typically below 1.2 V for PSC devices. Herein, for the first time an imidazole sulfonate zwitterion, 4‐(1H‐imidazol‐3‐ium‐3‐yl)butane‐1‐sulfonate (IMS), is applied as a bifunctional additive in regular‐structure planar heterojunction PSC devices to regulate the crystal orientation, yielding highly ordered MAPbI3 film and passivating the trap states of the film. Such a dual effect of IMS is fulfilled via coordination interactions between the sulfonate moiety of IMS with the Pb2+ ion and the electrostatic interaction between the imidazole of IMS with the I– ion of MAPbI3. As a result, under a optimized IMS doping ratio of 0.5 wt%, the PSC device exhibits a significant increase in PCE from 18.77% to 20.84%, with suppressed current–voltage hysteresis and promoted ambient stability. Moreover, a high Voc of 1.208 V is achieved under a higher IMS doping ratio of 1.2 wt%, which is the highest Voc for regular‐structure MAPbI3 planar PSC devices based on TiO2 electron transport layer. A bifunctional zwitterion additive affords efficiency enhancement of perovskite solar cells: an imidazole sulfonate zwitterion is doped into a CH3NH3PbI3 precursor solution as a bifunctional additive, enabling regulation of crystalline grain orientation and passivation of trap states. As a result, a significant efficiency enhancement and a high open circuit voltage (Voc) of 1.208 V are achieved.