Enhanced Charge Transport via Mixed-Dimensional Heterostructures in 2D-3D Perovskites and Their Relevance to Solar Cells

Two-dimensional and three-dimensional (2D-3D) mixed perovskites have shown noteworthy improvements in device performance and stability, owing to their hydrophobic nature and outstanding optoelectronic properties. However, the nature of the mixed-dimensional heterostructure and charge transport in 2D-3D perovskites is not clearly understood. In this study, we elucidate the effect of mixed-dimensional heterostructures on charge transport and their relevance to perovskite solar cells by changing the composition of 2D-3D mixed perovskites [(BA₂PbI₄)_x(MAPbI₃)_1-x, BA₂PbI₄as a 2D perovskite is added to 3D MAPbI₃, BA: butylamine, MA: methylammonium]. A small amount of BA₂PbI₄(x ≤ 0.02, x: nominal amount) enhances crystallinity by compact grain growth and improves charge transport by passivation of the grain boundary and an increase in conductivity. The trap passivation by sandwich-structured 2D-3D grains enhances the efficiency of the solar cell by 3%, and the mixed perovskite maintains the efficiency for 50 days (80% of the initial value). However, a large amount of 2D perovskite (x > 0.04) reduces the carrier lifetime and impedes charge transport due to poor conductivity. Furthermore, tuning of the 2D-3D perovskites modifies the electrical potential distribution near grain boundaries as well as the work function in perovskite absorbers and eventually alters the recombination of traps. Our study has thereby proven the improvement of charge transport and suggested a way to boost device performance of mixed 2D-3D perovskite solar cells.