Engineering Sr-doping for enabling long-term stable FAPb_1−xSr_xI₃ quantum dots with 100% photoluminescence quantum yield

The Pb substitution in quantum dots (PQDs) with lesser toxic metals has been widely searched to be environmentally friendly, and be of comparable or improved performance compared to the lead-perovskite. However, the chemical nature of the lead substitute influences the incorporation mechanism into PQDs, which has not been explored in depth. In this work, we analyzed Sr-doping-induced changes in FAPbI₃ perovskites by studying the optical, structural properties and chemical environment of FAPb_1−xSr_xI₃ PQDs. The substitution of Pb by 7 at% Sr allows us to achieve FAPb_1−xSr_xI₃ PQDs with 100% PLQY, high stability for 8 months under a relative humidity of 40–50%, and T₈₀ = 6.5 months, one of the highest values reported for halide PQDs under air ambient conditions. FAPb_0.93Sr_0.07I₃ PQDs also exhibit photobrightening under UV illumination for 12 h, recovering 100% PLQY at 15 days after synthesis. The suppression of structural defects mediated by Sr-doping decreases the non-radiative recombination mechanism. By attempting to increase the Sr content in PQDs, a mixture of 2D nanoplatelets/3D nanocubes has emerged, caused by a high Pb deficiency during the FAPb_1−xSr_xI₃ synthesis. This contribution gives a novel insight to understand how the suitable/poor Pb substitution achieved through Sr-doping dictates the photophysical properties of PQDs that may be potentially applicable in optoelectronics.