Dopant-Free Hole-Transporting Polycarbazoles with Tailored Backbones for Efficient Inverted Perovskite Solar Cells

Three conjugated polymers based on different linkage sites of carbazole repeat units, 3,6-PCzTPA, 2,7-PCzTPA, and 3,6-2,7-PCzTPA, were obtained through judicious molecular engineering. We observed that structure differences between 2,7- and 3,6-carbazole linkage sites could significantly influence intra- and intermolecular architectures and electronic states of materials. Herein, 3,6-PCzTPA and 3,6-2,7-PCzTPA with 3,6-carbazole units exhibited higher hole mobilities owing to the formation of radical cations, compared to 2,7-PCzTPA with 2,7-carbazole units. As a result, by using 3,6-2,7-PCzTPA as the hole-transporting material, perovskite solar cells with the p?i?n structure demonstrated the highest power conversion efficiency up to 18.4%. The outstanding device performance originated from compositive values of open-circuit voltage and fill factor, which were attributed to the suitable energy level as well as a high hole mobility of 3,6-2,7-PCzTPA. Moreover, its straightforward synthesis strategy, fine film-formation ability, and nondopant requirement indicated 3,6-2,7-PCzTPA as an ideal hole-transporting material for perovskite solar cells.