Efficient perovskite solar cells via surface passivation by a multifunctional small organic ionic compound

Abstract

Surface passivation is a proven strategy for preparing high efficiency planar perovskite solar cells. Herein, we report an effective surface passivation strategy using the multifunctional small organic ionic compound 1-ethylpyridinium chloride (EPC) in combination with (FAPbI₃)_0.95(MAPbBr₃)_0.05. It is found that the nitrogen atom in the pyridine group forms chemical bonds with under-coordinated lead ions in the perovskite film whereby the defect density is significantly reduced. The organic groups, including ethyl and pyridine, furthermore provide higher hydrophobicity for improved moisture stability. Finally, the chlorine anions were also found to play an important role in the defect passivation while further improving the perovskite crystallinity. Detailed theoretical study confirms that the EPC is indeed a good passivation agent for multiple defects. As a result, the power conversion efficiency is increased from 19.52% to as high as 21.19% via the EPC passivation and the devices show reduced hysteresis and increased stability.