Tailoring multifunctional anion modifiers to modulate interfacial chemical interactions for efficient and stable perovskite solar cells

The further development of perovskite solar cells (PSCs) is still restricted by high grain boundary density, interfacial defects, and interfacial energy barrier. Herein, we report a simple and effective universal anion modification strategy to increase the photovoltaic performance of PSCs, which is implemented through incorporating a series of guanidinium salts containing different anions (guanidinium thiocyanate (GASCN), guanidinium sulfate (GASO4), guanidine acetate (GAAc) and guanidine chloride (GACl)) to modify perovskite/SnO2 interface. All anions play a positive role in passivating the defects from surfaces of both SnO2 and perovskite layers, optimizing interfacial energy band alignment and facilitating the crystallization of PbI2 and perovskite. Moreover, different degrees of positive actions are found for different modifiers, which can be modulated by rational tailoring of anion species and thus interfacial chemical interaction. The relationships between chemical interaction strength, defect density, energy level, carrier lifetimes, crystallinity and device performance are established. The GASCN-, GA2SO4-, GAAc- and GACl-modified devices achieve a PCE of 22.76% 23.43%, 23.57% and 23.74%, respectively, which are much higher than 21.84% of the control device. Our obtained champion efficiency is among the highest efficiencies reported for the devices fabricated by sequential deposition method. Moreover, thermal and ambient stabilities are ameliorated after interface modification.