Dopant-free polymeric hole transport materials for efficient CsPbI2Br perovskite cells with a fill factor exceeding 84%

p-Type semiconductor PBDB-T and its derivatives have been explored as dopant-free hole transport materials for CsPbI₂Br inorganic perovskite solar cells, with PBDB-T-Si enabling a PCE of 15.6% and FF exceeding 84%.