Probing thermal stability in CsPbI3 quantum dots with coupled Pb-site doping and halide passivation

Abstract

All-inorganic CsPbI3 quantum dots (QDs) exhibit exceptional optoelectronic properties but suffer from poor thermal and structural stability, hindering their device integration. Here, we systematically investigate the temperature-dependent stability of pristine and Pb-site-substituted QDs combined with halide surface passivation, namely CsPb0.95Co0.05I3 and CsPb0.95Ag0.05I3, within the 20-80 degrees C range. Comprehensive X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL), time-resolved photoluminescence (TRPL), UV-visible absorption (UV-Vis), and Fourier-transform infrared (FTIR) measurements reveal that dual cation-halide doping (CoCl2 + CoI2 or AgCl + AgI) enhances lattice rigidity, mitigates thermal expansion, and suppresses nonradiative recombination. While pristine CsPbI3 QDs show alpha-phase distortion and emission quenching above 60 degrees C, doped QDs retain a cubic morphology and bright PL up to 80 degrees C. Lifetime analysis confirms reduced thermally activated nonradiative rates (Delta knr approximate to 6.7 x 10-3 ns-1 for Co2+-doped and 5.6 x 10-3 ns-1 for Ag+-doped versus 1.48 x 10-2 ns-1 for pristine QDs), evidencing significant trap suppression. The smallest lattice dilation (Delta d approximate to 0.6%) and minimal bandgap narrowing (Delta Eg approximate to 0.055 eV) observed in Ag-doped QDs demonstrate superior thermal robustness. These findings elucidate a synergistic stabilization mechanism in which B-site substitution strengthens lattice bonding and halide passivation reinforces surface anchoring, providing a practical route toward thermally durable CsPbI3-based optoelectronic materials.