Effects of impurities on the cooling of photoexcited carriers in La1−xSrxCoO3−δ: A DFT and nonadiabatic molecular dynamics study

Abstract

Photo-carrier relaxation in semiconductors determines their photon-conversion efficiency. Impurities have been proven to play an essential role in improving the efficiency and stability of perovskites. We studied the effects of Sr-doping and O-vacancies on the electronic band structure and photoexcited carrier cooling of perovskite-type LaCoO3 using density functional theory and nonadiabatic molecular dynamics methods. We found that the substitution of Sr2+ for La3+ in LaCoO3 leads to a semiconductor–metal transition, while a stoichiometric oxygen vacancy restores semiconductor properties in La1−xSrxCoO3−δ (δ = x/6). In addition, the oxygen vacancy basically changes the electronic band structures, and for visible light with low oxygen vacancy intensity, the photo-electron cooling can be reduced fourfold relative to that of pure LaCoO3. We clarify the functions of impurities, Sr-dopants, and O-vacancies in LaCoO3 and find that the average coupling strength between carriers (electrons/holes) and phonons can be used as a descriptor to characterize carrier relaxation, which is of great value for the further development of practical photo-conversion based on perovskites.