Reduction of Hole Carriers by van der Waals Contact for Enhanced Photoluminescence Quantum Yield in Two-Dimensional Tin Halide Perovskite

The role of electronic doping in determining the luminescence efficiency of low-dimensional halide perovskites has been challenging to test due to the structural complexity resulting from conventional dopant use. In this study, we demonstrate that van der Waals contact of aluminum (Al) onto a two-dimensional tin halide perovskite, phenethylammonium tin iodide (PEA 2 SnI 4 ), enhances photoluminescence (PL) intensity significantly, reaching a record-high PL quantum yield of 10%. The intensity relies on the contact metal type and reverts when the contact is released, demonstrating structural invariability. Ultraviolet photoemission spectroscopy reveals a 0.6 eV Fermi-level upshift caused by the Al contact, indicating a reduced hole concentration. Incident power-dependence and time-resolved PL suggest trap-assisted recombination as the primary nonradiative pathway. The Shockley-Read-Hall theory predicts suppression of trap-assisted recombination due to reduced free carrier concentration, providing a quantitative explanation for our findings. Our study emphasizes the significance of controlling electronic doping to optimize luminescence efficiency in low-dimensional perovskites.