Surface Termination on Unstable Methylammonium-based Perovskite Using a Steric Barrier for Improved Perovskite Solar Cells

Compared to widely adopted low-dimensional/three-dimensional (LD/3D) heterostructure, functional organic cation based surface termination on perovskite can not only realize advantage of defect passivation but also prevent potential disadvantage of the heterostructure induced intercalation into 3D perovskite. However, it is still very challenging to controllably construct surface termination on organic-inorganic hybrid perovskite because the functional organic cations' substitution reaction is easy to form LD/3D heterostructure. Here, we report using a novel benzyltrimethylammonium (BTA) functional cation with rational designed steric hindrance to effectively surface terminate onto methylammonium lead triiodide (MAPbI3) perovskite, which is composed of the most unstable MA cations. The BTA cation is difficult to form a specific 1.5-dimensional perovskite of BTA4Pb3I10 by cation substitution with MA cation, which then provides a wide processing window (around 10 minutes) for surface terminating on MAPbI3 films. Moreover, the BTAI surface terminated BTAI-MAPbI3 shows better passivation effect than BTA4Pb3I10-MAPbI3 heterojunction. Finally, BTAI surface terminated solar cell (0.085 cm2) and mini-module (11.52 cm2) obtained the efficiencies of 22.03 % and 18.57 %, which are among the highest efficiencies for MAPbI3 based ones. Surface termination can passivate perovskite films and avoid the degradation of low-dimensional/three-dimensional (LD/3D) heterojunctions, but it's difficult to realize surface termination to hybrid perovskites due to the fast cation exchange. Here, a benzyltrimethylammonium cation with rational designed steric barrier can effectively surface terminate methylammonium lead iodide (MAPbI3) with a wide processing window and enhanced stability.image

Automated summary

Functional organic cation based surface termination on perovskite has the advantage of defect passivation and the prevention of intercalation into 3D perovskite. However, controlling the surface termination on organic-inorganic hybrid perovskite is challenging. In this study, we used a novel benzyltrimethylammonium (BTA) functional cation with steric hindrance to effectively surface terminate methylammonium lead triiodide (MAPbI3) perovskite, achieving a wide processing window and enhanced stability.