2D WSe₂ Flakes for Synergistic Modulation of Grain Growth and Charge Transfer in Tin-Based Perovskite Solar Cells

Tin (Sn)-based perovskites with favorable optoelectronic properties and ideal bandgaps have emerged as promising alternatives to toxic lead (Pb)-based perovskites for photovoltaic applications. However, it is challenging to obtain high-quality Sn-based perovskite films by solution process. Here, liquid-exfoliated 2D transition-metal dichalcogenides (i.e., MoS₂, WS₂, and WSe₂) with smooth and defect-free surfaces are applied as growth templates for spin-coated FASnI₃ perovskite films, leading to van der Waals epitaxial growth of perovskite grains with a growth orientation along (100). The authors find that WSe₂ has better energy alignment with FASnI₃ than MoS₂ and WS₂ and results in a cascade band structure in resultant perovskite solar cells (PSCs), which can facilitate hole extraction and suppress interfacial charge recombination in the devices. The WSe₂-modified PSCs show a power conversion efficiency up to 10.47%, which is among the highest efficiency of FASnI₃-based PSCs. The appealing solution phase epitaxial growth of FASnI₃ perovskite on 2D WSe₂ flakes is expected to find broad applications in optoelectronic devices.