Environmental‐Friendly Urea Additive Induced Large Perovskite Grains for High Performance Inverted Solar Cells. Issue 7 (25th April 2018) - Han, Liang
Abstract : It is a challenge to grow perovskite films with large crystalline grains and a full coverage on the surface of an organic compound film by a solution process. Herein, we for the first time introduce environmental‐friendly urea into PbI2 precursor to mediate the perovskite film growth and crystallization on the top of PEODT:PSS for efficient inverted solar cells. This method attains high‐quality perovskite films with large‐size grains of over 2 μm and a full coverage. This enables us to fabricate the inverted perovskite solar cells showing a maximum efficiency of 18.01% with a fill factor of 82.29% and a stabilized efficiency of 17.56%. Infrared spectroscopy and scanning electron microscopy images demonstrate that urea is coordinated with PbI2 to form PbI2 · OC(NH2 )2 complex, resulting in large PbI2 flakes by a slow crystallization. The large PbI2 flake with fewer nucleation sites is conducive to forming monolithic perovskite grains. Further investigation indicates that CH3 NH3 I · PbI2 · OC(NH2 )2 complex is formed as an intermediate phase, which retards the crystallization process of the perovskite films. These factors lead to a high‐quality perovskite film with large grain size and excellent crystallinity. Abstract : Urea is introduced into PbI2 precursor to mediate PbI2 film growth by an intermediate phase of PbI2 · OC(NH2 )2 . The experiment demonstrates that slow crystallization contributes to formation of large PbI2 flakes with fewer nucleation sites rendering growth of perovskite grains over 2 μm. The resultant solar cell exhibits excellent performance.