Polar molecule as passivation agent towards enhanced carrier transport properties in perovskite solar cells

Abstract

Defect passivation using aryl ammonium salts have been proved as a feasible way to promote the efficiency and stability of perovskite solar cells (PSCs). However, the design criterion is still no clear. Herein, a series of diammonium iodides were used as passivators on the perovskite surface. We find that in situation of diammonium salts, carrier transport ability is more important than their pKa values. And passivator molecules with high polarity would lead to improved carrier transport and then mitigated nonradiative recombination in PSCs due to the enhanced induced electric field and high carrier mobility. As a result, cell 3 (passivator with a pKa of 3.69 and high polarity) show superior PCE (21.59%) and stability than the control PSCs, but other devices with low polarity passivators show worse transport and poorer performance, despite their higher pKa (cell 4 and 5) or better energy level (cell 1). This work proposes a way to design passivators with enhanced carrier transport properties for PSCs.