Very high hole drift mobility in neat and doped molecular thin films for normal and inverted perovskite solar cells

Hole transporting layers (HTLs) have critical roles in the performance of perovskite solar cells. In this study, films of the vacuum-deposited small molecule of Tris[4-(5-phenylthiophene-2-yl) phenyl] amine (TPTPA) are demonstrated as efficient HTL materials for perovskite solar cells. The horizontal molecular stacking of the TPTPA neat film leads to the exceptionally high hole drift mobility of 7 x 10(-3) cm(2) V-1 s(-1), among the highest values observed in the organic molecular neat films. By doping with MoO3, a clear charge transfer state is formed and the hole mobility further increases to 3.6 x 10(-2) cm(2) V-1 s(-1). Both normal-and inverted-structured perovskite solar cells utilizing these HTLs are prepared and optimized; they show high power conversion efficiencies of 17-18%.