Dopant-free Hole-transporting Materials for CH3NH3PbI3 Inverted Perovskite Solar Cells with an Approximate Efficiency of 20%

A D-pi-A-pi-A-pi-D structure-based small organic molecule (YJ01) has been demonstrated as an efficient dopant-free hole-transporting material (HTM) for inverted perovskite solar cells (iPSCs). The conjugation and twisted angles are balanced by the 1,4-di((E)-styryl)benzene core that bears two electron-withdrawing cyan groups. The cyan positions on the central core have a significant impact on the HTM properties. The outstanding performance of the iPSC device employing indium-doped tin oxide/pristine HTM/CH3NH3PbI3/PCBM/BCP/Ag based on YJ01 yielded an efficiency of 19.85% with a Voc of 1.08 V, Jsc of 22.53 mA cm(-2), and FF of 0.815. The device which was based on YJ02 yielded power conversion efficiency (PCE) of 17.5%. The devices retained 80% of their original PCE after 500 h in an ambient environment. The hole motilities of YJ01 and YJ02 were determined to be 5.68 x 10(-3) cm(2) V-1 s(-1) and 1.55 x 10(-3) cm(2) V-1 s(-1), respectively. The large efficiency difference between YJ01 and YJ02 is attributed to the enlargement of the substitution distance between the two cyan units given the much greater reduction of solid-state fluorescence emission for YJ01 compared with YJ02. Thus, it is hoped to provide a good strategy for the HTM design, facilitating highly efficient and stable iPSCs.