Surface ion exchange and targeted passivation with cesium fluoride for enhancing the efficiency and stability of perovskite solar cells

Interfacial defects greatly influence the performance of perovskite solar cells (PSCs), and interface engineering is a powerful technique to promote the power conversion efficiency (PCE) of PSCs. Herein, an interfacial passivation strategy is developed employing cesium fluoride (CsF) to modify the surface of a perovskite film. Theoretical calculations suggest that the Cs+ and F- ions have a targeted passivation effect to decrease the defect density of the perovskite. Meanwhile, Cs+-formamidine(+) (FA(+)) and F--I- ion exchange can occur on the perovskite surface, which leads to the decline of the Fermi level of perovskite and reinforces the built-in potential of PSCs. Additionally, experiment results also confirm the reduction in the interfacial defects and the enhancement of the built-in potential. Consequently, the open-circuit voltage (V-oc) of PSCs is increased from 1.07 to 1.12 V, contributing to the promotion of the PCE. Furthermore, the stability of PSCs is obviously improved as well owing to the suppressed phase transition of alpha-phase perovskite. Our findings provide guidelines for surface modification of perovskite crystals to enhance the performance and stability of PSCs. Published under an exclusive license by AIP Publishing.

Automated summary

This study develops a method of using cesium fluoride to improve the surface of perovskite films, reducing their defect density and enhancing the built-in potential of PSCs. Experimental results show that this method significantly increases the open-circuit voltage of PSCs and improves their stability.