Bright Tin Halide Perovskite Quantum Dots via Organic Dication Compensatory Doping

Tin halide perovskite quantum dots (THP QDs) are promising alternatives to their lead analogs for red and near-infrared emission. However, cation vacancies cause strong p-doping, limiting the photoluminescence quantum yields (PLQYs) of quantum-confined THP QDs. Low formation energies of charged cation vacancies hinder doping control through stoichiometry alone, while effective aliovalent doping strategies for extrinsic control of carrier concentrations remain lacking. Here, we establish organic dications, such as ethylenediammonium (EN), as effective electron-donor dopants for THP QDs. Aliovalent A-cation substitution compensates the p-character, enhancing the PLQY by over two orders of magnitude. CsSnI₃-EN QDs ranging in size from 4 to 16 nm emit beyond 750 nm with PLQYs up to 38%. Enhancements extend to various dications and hybrid FASnI₃ QDs. The pristine, hole-doped THP QDs exhibit a size-dependent infrared absorption band arising from valence-to-valence intraband transitions, which disappears upon compensatory EN doping. X-ray photoelectron spectroscopy reveals increased core-level binding energies for all three perovskite constituents, consistent with a Fermi level shift of approximately 0.1 eV away from the valence band. Density functional theory calculations corroborate this finding and elucidate the defect equilibria. These results establish organic dications as donor dopants for near-infrared emissive THP QDs.