Unravelling the Role of Surface Traps on Carrier Relaxation and Transfer Dynamics in Ultrasmall Semiconductor Nanocrystals

Charge carrier trapping by the surface defects of colloidal semiconductor nanocrystal (NC) is a ubiquitous process which limits the performance of NC-based photovoltaic and photocatalytic devices. Although several empirical approaches led to the enhancement of device efficiency via passivation of trap states, a systematic and unified description of trapping mechanism remains obscure. In this contribution, we present a detailed experimental investigation of the carrier dynamics of CdSe NCs with varying concentration of surface traps by means of time-resolved photoluminescence (PL) and absorption. Our study reveals that the rate of carrier cooling becomes faster as trap density increases because of the increased hot carrier trapping. A comparative dynamical study is also presented to demonstrate how trap states influence electron injection process. This enhanced understanding of the role of trap sates on charge carrier dynamics can provide valuable insight toward the rational development of more efficient NC-based optoelectronic devices.