Organic Cation Engineering for Vertical Charge Transport in Lead‐Free Perovskite Quantum Wells.

2D organic–inorganic hybrid halide perovskites are promising semiconductor materials for a variety of device applications. However, fundamental issues of charge transport through multiple quantum wells separated by bulky organic ligands remain unsolved. Herein, a mixture of π‐conjugated organic ligands, (2‐(3‴,4′‐dimethyl‐[2,2′:5′,2′:5″,2‴‐quaterthiophen]‐5‐yl)ethan‐1‐ammonium iodide) (4Tm) and 2‐([2,2′‐bithiophen]‐5‐yl)ethan‐1‐aminium iodide (2T), is used as spacer to form (4Tm)x(2T)2−xSnI4 2D perovskite thin films. The new strategy of alloying 2T into 4Tm ligands reduces the interlayer distance (barrier thickness) while maintaining the relatively small energy barrier height for the hybrid quantum wells, enhances interlayer interactions, and improves charge transport across adjacent perovskite layers. Moreover, solar cell devices fabricated with (4Tm)x(2T)2−xSnI4 exhibit improved photovoltaic properties and stability. [ABSTRACT FROM AUTHOR]