Ionic liquid induced surface trap-state passivation for efficient perovskite hybrid solar cells

Abstract

The highly crystalline methylammonium lead halides (MALHs) perovskite has large carrier diffusion length and thus minimal charge loss within the MALHs layers. But the charge extraction from the perovskite to the charge extraction layers can be significantly influenced by the interfacial contact. Since the fast-crystalized MALHs usually have a rough surface with numerous trap-states and crystal grain boundaries near the top surface, which will deteriorate the electrical coherence and physical contact with the top electron extraction layer (EEL) in the conventional device structure. In this study, we introduced an ionic liquid methyltrioctylammonium trifluoromethanesulfonate (MATS) to passivate the traps and boundaries at the interface of the i-n junction. The photoluminance results demonstrated an improved electron extraction upon the MATS surface treatment. And the impedance measurements also showed a reduced charge transfer resistance within the MATS treated device. Consequently, the conventional planar heterojunction solar cells based on the MALHs perovskite treated by MATS, showed an enhanced device efficiency of 16.10%. Moreover, after heating at elevated temperatures under 2 V forward bias and cooling down to room temperature, we found the MATS modified solar cell devices exhibit a further efficiency improvement to 17.51%.