Novel dopant-free hole transport materials enabling 20.9% efficiency in perovskite solar cells

Two novel donor-acceptor-donor (D-A-D) type dopant-free hole transport materials (HTMs), named BDD-T and BTT-T, were developed and applied in perovskite solar cells. An impressive power conversion efficiency (PCE) of 20.9% was acquired, which is one of the highest PCEs for D-A-D type dopant-free HTMs.