Tri-Brominated Perovskite Film Management and Multiple-Ionic Defect Passivation for Highly Efficient and Stable Solar Cells

High-quality perovskite films with low imperfections, high hole mobility, and matching energy levels play a crucial role in enhancing performance of perovskite solar cells (PSCs) without hole-transporting materials (HTMs). Herein, it is demonstrated that the incorporation of a stable tetra-bisphenol A (TBBPA) with diphenyl ring, polybromides, and hydroxyl groups additive into a perovskite film can simultaneously manipulate the crystal growth and passivate the defects through coordination interaction between the functional group (-OH, -Br) and the unsaturated halogen and metal ions (Br-, Cs+, and Pb2+), resulting in a reduced grain boundary as well as imperfection and increased hole mobility of the CsPbBr3 perovskite film. In addition, the valence band of a perovskite film with TBBPA additive is shifted upward to approach the work function of the carbon electrode, thereby improving the energy level alignment. Consequently, a significantly boosted charge extraction and reduced charge recombination of the carbon-based HTM-free CsPbBr3 PSCs is obtained after incorporating the TBBPA additive, yielding a maximum power conversion efficiency of up to 9.82% of the optimized device. Furthermore, the champion PSC without encapsulation displays a remarkable thermal and moisture stability after being kept in ambient air for 720 h at 85 degrees C and 85% relative humidity, respectively.

Automated summary

The study demonstrates that adding TBBPA to perovskite films can manipulate crystal growth and passivate defects, improving hole mobility and energy level alignment of CsPbBr3 perovskite films, resulting in significantly enhanced performance of PSCs.