Chemical nanoimaging of octylphosphonic acid molecular additives on hybrid organic–inorganic perovskite films

Abstract

Defect passivation using additives has been demonstrated to be an effective approach to improve the efficiency and stability of perovskite devices. However, understanding the interactions and bonding state between additives and the film surface at the molecular level has been a long-standing challenge, due to the trace concentration of additives and the surface heterogeneity of perovskite films. Herein, by employing a non-destructive and label-free infrared nanospectroscopy technique, we achieved the experimental observations of inhomogeneously distributed additives on the surface of a hybrid organic–inorganic perovskite film, with spatial resolution down to 10 nm. For the first time, the association between the octylphosphonic acid (OPA) molecule and FA_0.9MA_0.05Cs_0.05PbI₃ film has been revealed at the molecular level. Chemical nanoimaging revealed that OPA additives were chiefly filled at the edges of the perovskite grain boundaries. With a higher spatial resolution of chemical nanoimaging, the OPA additive molecules were detected at the sub-grain boundary showing distinct cascade distribution characteristics. The analysis of the effect of OPA on the environmental stability of the perovskite proves a comprehensive passivation effect on the surface defect and the decomposition of organic components in perovskite thin films. Our work demonstrates an efficient approach for chemical nanoimaging of perovskites and provides a new spectroscopic insight into the modulation of additives on perovskites.