Stabilization of Highly Efficient and Stable Phase‐Pure FAPbI3 Perovskite Solar Cells by Molecularly Tailored 2D‐Overlayers

• Published in: Angewandte Chemie International Edition 2020-09, Vol.59 (36), p.15688-15694
• Main Authors: Liu, Yuhang, Akin, Seckin, Hinderhofer, Alexander, Eickemeyer, Felix T., Zhu, Hongwei, Seo, Ji‐Youn, Zhang, Jiahuan, Schreiber, Frank, Zhang, Hong, Zakeeruddin, Shaik M., Hagfeldt, Anders, Dar, M. Ibrahim, Grätzel, Michael
• Format: Article
• Language: English
• Subjects: additive engineering; Cations; Energy conversion efficiency; FAPbI3; Iodides; Maximum power tracking; Metal halides; Optoelectronics; perovskite solar cells; Perovskites; Photovoltaic cells; Solar cells; Solar power; Thermal stability
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202005211

As a result of their attractive optoelectronic properties, metal halide APbI3 perovskites employing formamidinium (FA+) as the A cation are the focus of research. The superior chemical and thermal stability of FA+ cations makes α‐FAPbI3 more suitable for solar‐cell applications than methylammonium lead iodide (MAPbI3). However, its spontaneous conversion into the yellow non‐perovskite phase (δ‐FAPbI3) under ambient conditions poses a serious challenge for practical applications. Herein, we report on the stabilization of the desired α‐FAPbI3 perovskite phase by protecting it with a two‐dimensional (2D) IBA2FAPb2I7 (IBA=iso‐butylammonium overlayer, formed via stepwise annealing. The α‐FAPbI3/IBA2FAPb2I7 based perovskite solar cell (PSC) reached a high power conversion efficiency (PCE) of close to 23 %. In addition, it showed excellent operational stability, retaining around 85 % of its initial efficiency under severe combined heat and light stress, that is, simultaneous exposure with maximum power tracking to full simulated sunlight at 80 °C over 500 h. The desired α‐FAPbI3 perovskite phase is stabilized by protecting it with a two‐dimensional (2D) IBA2FAPb2I7 (IBA=iso‐butylammonium) overlayer, formed via stepwise annealing. The α‐FAPbI3/IBA2FAPb2I7‐based perovskite solar cell (PSC) reached a high power conversion efficiency (PCE) of close to 23 %. It showed excellent operational stability, retaining around 85 % of its initial efficiency under severe combined heat and light stress.