Liu Yuxiang, Frauenheim Thomas, Yam ChiYung
Bremen Center for Computational Materials Science, University of Bremen, Am Fallturm 1, 28359, Bremen, Germany.
Beijing Computational Science Research Center, Haidian District, Beijing, 100193, China.
Adv Sci (Weinh). 2022 Nov;9(31):e2203400. doi: 10.1002/advs.202203400. Epub 2022 Sep 7.
Carrier multiplication (CM), multiexciton generation by absorbing a single photon, enables disruptive improvements in photovoltaic conversion efficiency. However, energy conservation constrains the threshold energy to at least twice bandgap (2 ). Here, a below threshold limit CM in monolayer transition metal dichalcogenides (TMDCs) is reported. Surprisingly, CM is observed with excitation energy of only 1.75 due to lattice vibrations. Electron-phonon coupling (EPC) results in significant changes in electronic structures, which favors CM. Indeed, the strongest EPC in monolayer MoS leads to the most efficient CM among the studied TMDCs. For practical applications, chalcogen vacancies can further lower the threshold by introducing defect states within bandgap. In particular, for monolayer WS , CM occurs with excitation energy as low as 1.51 . The results identify TMDCs as attractive candidate materials for efficient optoelectronic devices with the advantages of high photoconductivity and efficient CM.
载流子倍增（CM），即通过吸收单个光子产生多激子，能够显著提高光伏转换效率。然而，能量守恒将阈值能量限制在至少两倍带隙（2 ）。在此，报道了单层过渡金属二硫属化物（TMDCs）中的低于阈值限制的CM。令人惊讶的是，由于晶格振动，在仅1.75 的激发能量下就观察到了CM。电子 - 声子耦合（EPC）导致电子结构发生显著变化，这有利于CM。实际上，单层MoS中最强的EPC导致在所研究的TMDCs中CM效率最高。对于实际应用，硫族空位可以通过在带隙内引入缺陷态进一步降低阈值。特别是，对于单层WS ，在低至1.51 的激发能量下就会发生CM。这些结果表明，TMDCs具有高光导率和高效CM的优点，是高效光电器件有吸引力的候选材料。
