Surface energetics mediated charge transfer and exciton transfer in cation-adsorbed rubrene/PbS nanocrystal hybrids

Abstract

Organic molecule and inorganic nanocrystal hybrids have become a promising platform for photon energy conversion. Although surface energetics modification was proven effective in promoting triplet energy transfer, singlet energy transfer and charge transfer have been barely investigated. Here, we systematically clarify the photophysical dynamics of charge, singlet exciton, and triplet exciton among the energy conversion process based on hybrids of rubrene and Cd2+-adsorbed PbS nanocrystals. It is found that a considerable amount of charges in rubrene molecules can be transferred to cation-induced surface states in ~2 ps time scale with high efficiency to trigger a delayed biexciton effect, which provides a novel approach to uncover the intermediate role of nanocrystal surface sates. For triplet exciton, strong interaction with surface states is investigated with a recycling energy transfer around 14% efficiency, which is found insensitive to changes in nanocrystal surface energetics. As a result, the maximum photoluminescence lifetime of PbS nanocrystals was enhanced by about 38%. This work reveals the neglected photo-physical dynamics in the transfer process between organic molecules/inorganic nanocrystals and validates the capability of surface state in sensitization of organic charges and excitons.