Caffeine Improves the Performance and Thermal Stability of Perovskite Solar Cells
Rui Wang,1,5 Jingjing Xue,1,5 Lei Meng,1 Jin-Wook Lee,1 Zipeng Zhao,1 Pengyu Sun,1 Le Cai,1 Tianyi Huang,1 Zhengxu Wang,1 Zhao-Kui Wang,1,2,* Yu Duan,1,3 Jonathan Lee Yang,1,6 Shaun Tan,1 Yonghai Yuan,4 Yu Huang,1 and Yang Yang1,7,*
1Department of Materials Science and Engineering and California NanoSystems Institute, University of California Los Angeles, Los Angeles, CA 90095, USA
2Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University, Suzhou 215123, China
3State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China
4Solargiga Energy Holdings Limited, Hong Kong 999077, China
To increase the commercial prospects of metal halide perovskite solar cells, there is a need for simple, cost-effective, and generalized approaches that mitigate their intrinsic thermal instability. Here we show that 1,3,7 trimethylxanthine, a commodity chemical with two conjugated carboxyl groups better known by its common name caffeine, improves the performance and thermal stability of perovskite solar cells based on both MAPbI3 and CsFAMAPbI3 active layers. The strong interaction between caffeine and Pb2+ ions serves as a ‘‘molecular lock’’ that increases the activation energy during film crystallization, delivering a perovskite film with preferred orientation, improved electronic properties, reduced ion migration, and greatly enhanced thermal stability. Planar n-i-p solar cells based on caffeine-incorporated pure MAPbI3 perovskites, which are notoriously unstable, exhibit a champion stabilized efficiency of 19.8% and retain over 85% of their efficiency under continuous annealing at 85℃ in nitrogen.