Characterization of hot carrier cooling and multiple exciton generation dynamics in PbS QDs using an improved transient grating technique

作     者：Qing Shen Kenji Katayama Taro Toyoda 

作者机构：Department of Engineering ScienceFaculty of Informatics and EngineeringThe University of Electro-Communications Department of Applied ChemistryFaculty of Science and EngineeringChuo University 

出 版 物：《Journal of Energy Chemistry》 (能源化学（英文版）)

年 卷 期：2015年第24卷第6期

页      面：712-716页

核心收录：

学科分类：0820[工学-石油与天然气工程] 0808[工学-电气工程] 081704[工学-应用化学] 07[理学] 0817[工学-化学工程与技术] 08[工学] 0807[工学-动力工程及工程热物理] 0827[工学-核科学与技术] 0703[理学-化学] 070301[理学-无机化学] 

基　　金：supported by MEXT KAKENHI Grant no. 26286013 the PRESTO program Photoenergy conversion systems and materials for the next generation solar cells,Japan Science and Technology Agency (JST) 

主　　题：PbS Quantum dots Multiple exciton generation Hot carrier cooling Transient grating 

摘      要：Multiple exciton generation （MEG） dynamics in colloidal PbS quantum dots （QDs） characterized with an im- proved transient grating （TG） technique will be reported. Only one peak soon after optical absorption and a fast decay within 1 ps can be observed in the TG kinetics when the photon energy of the pump light hv is smaller than 2.7Eg （Eg： band gap between LUMO and HOMO in the QDs）, which corresponds to hot carrier cooling. When hv is greater than 2.7Eg, however, after the initial peak, the TG signal decreases first and soon increases, and then a new peak appears at about 2 to 3 ps. The initial peak and the new peak correspond to hot carriers at the higher excited state and MEG at the lowest excited state, respectively. By proposing a theoretical model, we can calculate the hot carrier cooling time constant and MEG occurrence time constant quantitatively. When MEG does not happen for hv smaller than 2.7Eg, hot carrier cools with a time con- stant of 400 fs. When MEG occurs for hv larger than 2.7Eg, hot carrier cools with a time constant as small as 200 fs, while MEG occurs with a time constant of 600 fs. The detailed hot carrier cooling and MEG occurrence dynamics characterized in this work would shed light on the further understanding of MEG mechanism of various type of semiconductor QDs.