Modulation of the optical bandgap and photoluminescence quantum yield in pnictogen (Sb³⁺/Bi³⁺)-doped organic–inorganic tin(IV) perovskite single crystals and nanocrystals

Water-stable, lead-free zero-dimensional (0D) organic–inorganic hybrid colloidal tin(IV) perovskite, A₂SnX₆ (A is a monocationic organic ion and X is a halide) nanocrystals (NCs) with high photoluminescence (PL) quantum yield (QY) have rarely been explored. Herein, we report solution-processed colloidal NCs of blue light-emitting T₂SnCl₆ and orange light-emitting T₂Sn_1-xSb_xCl₆ [T⁺ = tetramethylammonium cation] from their corresponding single crystals (SCs). These colloidal NCs are well-dispersible in non-polar solvents, thereby maintaining their bright emission. This paves the way for fabricating homogeneous thin films of these NCs. Due to organic cation (T⁺)-controlled large spin–orbit coupling (SOC), the T₂Sn_1-xSb_xCl₆ NCs exhibit bright orange emission with an enhancement in PL QY of 41% compared to their bulk counterpart. Furthermore, we explore T₂Sn_1-xBi_xCl₆ and T₂Sn_1-x-yBi_xSb_yCl₆ SCs, which show blue and green emission, respectively; the latter is attributed to the newly formed Sb 5p and Sb 5 s orbital-driven band structures confirmed by applying density functional theory (DFT) calculations. The SCs and NCs exhibit excellent stability in water under ambient conditions because of the in-situ generation of a hydrophobic and oxygen-resistant passivating layer of oxychloride in the presence of water. Our findings open a pathway for designing lead-free perovskites materials for thin-film-based optoelectronic devices.