Intraband Cooling in All-Inorganic and Hybrid Organic-Inorganic Perovskite Nanocrystals

Intraband relaxation in all-inorganic cesium lead tribromide (CsPbBr3) and hybrid organic-inorganic formamidinium lead tribromide (FAPbBr(3)) nanocrystals is experimentally investigated for a range of particle sizes, excitation energies, sample temperatures, and excitation fluences. Hot carriers in CsPbBr3 nanocrystals consistently exhibit slower cooling than FAPbBr(3) nanocrystals in the single electron-hole pair per nanocrystal regime. In both compositions, long-lived hot carriers (>3 ps) are only observed at excitation densities corresponding to production of multiple electron-hole pairs per nanocrystal-and concomitant Auger recombination. These presented results are distinct from previous reports in bulk hybrid perovskite materials that convey persistent hot carriers at low excitation fluences. Time-resolved photoluminescence confirms the rapid cooling of carriers in the low-fluence (single electron-hole pair per nanocrystal) regime. Intraband relaxation processes, as a function of excitation energy, size, and temperature are broadly consistent with other nanocrystalline semiconductor materials.