Enhanced Hot‐Phonon Bottleneck Effect on Slowing Hot Carrier Cooling in Metal Halide Perovskite Quantum Dots with Alloyed A‐Site

Abstract

A deep understanding of the effect of the A-site cation cross-exchange on the hot-carrier relaxation dynamics in perovskite quantum dots (PQDs) has profound implications on the further development of disruptive photovoltaic technologies. In this study, the hot carrier cooling kinetics of pure FAPbI₃ (FA⁺ , CH(NH₂ )₂ ⁺ ), MAPbI₃ (MA⁺ , CH₃ NH₃ ⁺ ₊ ), CsPbI₃ (Cs⁺ , Cesium) and alloyed FA_0.5 MA_0.5 PbI₃ , FA_0.5 Cs_0.5 PbI₃ , and MA_0.5 Cs_0.5 PbI₃ QDs are investigated using ultrafast transient absorption (TA) spectroscopy. The lifetimes of the initial fast cooling stage (<1 ps) of all the organic cation-containing PQDs are shorter than those of the CsPbI₃ QDs, as verified by the electron-phonon coupling strength extracted from the temperature-dependent photoluminescence spectra. The lifetimes of the slow cooling stage of the alloyed PQDs are longer under illumination greater than 1 sun, which is ascribed to the introduction of co-vibrational optical phonon modes in the alloyed PQDs. This facilitated efficient acoustic phonon upconversion and enhanced the hot-phonon bottleneck effect, as demonstrated by first-principles calculations.