Efficient and stable CsPbI3 perovskite solar cells with spontaneously formed 2D-Cs2PbI2Cl2 at the buried interface
Syed Fawad Ali Shah, Inyoung Jeong, Jaewang Park, Jaewang Park, Donghyeop Shin, Inchan Hwang, Nikolai Tsvetkov, Dohyung Kim, Jihye Gwak, Joo Hyung Park, Joo Hyung Park, Sang Il Seok, Kihwan Kim, Hanul Min
Abstract
Despite its nature of superior thermal and photostability compared to the mixed cation or halide counterparts, cesium lead triiodide (CsPbI 3 ) suffers from the undesired phase transition from β phase to δ phase, which is often initiated at the buried interface. In this study, we demonstrate that the addition of Cl induces the spontaneous formation of the two-dimensional (2D) Ruddlesden-Popper (RP) phase of Cs 2 PbI 2 Cl 2 . The 2D RP Cs 2 PbI 2 Cl 2 predominantly forms at the buried interface due to Cl segregation, improving the electron transfer and phase stability of the CsPbI 3 thin films. Perovskite solar cells based on CsPbI 3 /Cs 2 PbI 2 Cl 2 light absorbers exhibited a power conversion efficiency (PCE) of 20.6% (with a stabilized efficiency of 20.1%) under simulated solar illumination. Furthermore, the unencapsulated devices retained approximately 80% of their initial PCEs after continuous light exposure for 1,000 h.