The strain regulation of atomic structure and properties on ultra-stable monolayer butylammonium-based halide perovskites: Insight from density functional theory

Abstract

The two-dimensional (2D) monolayer butylammonium (BA)-based halide perovskites are applied for perovskite solar cells (PSCs) due to ultra-stable and highly crystalline. However, the systematic analysis has not been well conducted for 2D monolayer (BA)2BX4 (BPb, Sn; X = I, Br, Cl) perovskites. Here we systematically investigated the photoelectric and mechanical properties using density functional theory (DFT), further revealing the effect and mechanism of the direct and doping-modulated strain induced by external strain(stress) and pre-strain treatment technology. (BA)2PbI4, (BA)2SnI4 and (BA)2SnBr4 have excellent properties for PSCs. Based on the direct strain regulation, (BA)2SnBr4 exhibits smaller bandgaps and more stable atomic evolution than (BA)2PbI4, and better mechanical properties and smaller electrostatic macroscopic average potential difference (ΔP) than (BA)2SnI4. Based on the doping-modulated strain regulation on 2D (BA)2(Pb1-xSnx)X4, lower Pb-doping ratio induces the nonlinear dependence of bandgaps, which mainly originating from the local compressive strain effect on Sn crystal structure induced by larger Pb-atomic radius. Especially, the double-decker structure (Sn2Pb2-p) obtains excellent stability due to stress relaxation induced by in-inorganic layer homogeneity. We anticipate this work will provide the sufficient guidance for designing and fabricating green 2D or 2D/3D halide junction PSCs to improve both PCE and stability.