Singlet relaxation dynamics and long triplet lifetimes of thiophene-coupled perylene diimides dyads: New insights for high efficiency organic solar cells

被引:12
作者
Fan, Qingxuan [1 ]
Ni, Wenjun [2 ]
Chen, Lingcheng [1 ]
Gurzadyan, Gagik G. [2 ]
Xiao, Yi [1 ]
机构
[1] Dalian Univ Technol, State Key Lab Fine Chem, Dalian 116024, Peoples R China
[2] Dalian Univ Technol, Inst Artificial Photosynth, State Key Lab Fine Chem, Dalian 116024, Peoples R China
基金
中国国家自然科学基金;
关键词
Ultrafast relaxation dynamics; Triplet excited state; Exciton lifetime; Photophysical process; Organic solar cell; STACKED PERYLENE-3,4/9,10-BIS(DICARBOXIMIDE) DIMERS; LIGHT-EMITTING-DIODES; RING-FUSION; EXCIMER FORMATION; STATE FORMATION; PERFORMANCE; DESIGN; ABSORPTION; BODIPY; PHOTOSENSITIZERS;
D O I
10.1016/j.cclet.2020.06.018
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
In the active layer of organic solar cells (OSCs), the lifetime of triplet excitons is one of the decisive factors in the diffusion length and therefore has important impact on the power conversion efficiency of the devices. Herein, we have investigated singlet excited state relaxation dynamics and their triplet exciton lifetimes of two thiophene-coupled perylene diimides (PDI) dyads (2PDI-Th and fused-2PDI-Th), in order to provide a unique explanation in depth on their different performances in OSC devices. From the transient absorption (TA) spectra, the singlet excitons of 2PDI-Th form excimers in the time scale of 1.5 ps. Then the excimers go into the triplet state via intersystem crossing (ISC). In fused-2PDI-Th, triplet excitons are generated directly from the singlet excited excitons via the efficient ISC. Density functional theory (DFT) calculations further support the formation of excimers. DFT results indicate that 2PDI-Th exhibits an H-typed molecular configuration which is beneficial to form the excimers, while fused-2PDITh gives a twisted X-shaped configuration in the optimized ground and excited state. In steady-state emission spectra, 2PDI-Th shows abroad and featureless spectral characteristics of the excimers with a decay time of 840 ps, which is much shorter than those of PDI (5.5 ns) and fused-2PDI-Th (3.3 ns). The triplet lifetime (67 ms) of fused-2PDI-Th is factor of 3 longer than that of 2PDI-Th (22 ms). These results demonstrate that ring-fused structure is an efficient strategy to eliminate excimer formation and prolong the lifetime of triplet excitons, which provides a new insight for design of optoelectronic molecules for high efficiency organic solar cells. (C) 2020 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.
引用
收藏
页码:2965 / 2969
页数:5
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