Identification of a bridge-specific intramolecular exciton dissociation pathway in donor–π–acceptor alternating conjugated polymers

Nanoscale Research Letters

Zhongpo Zhou¹  Yufang Liu¹  Tingting Jiang¹  Zhaoyong Jiao¹  Chaochao Qin¹  Yuhai Jiang²  Jinyou Long³ 

[1] Henan Key Laboratory of Infrared Materials and Spectrum Measures and Applications, School of Physics, Henan Normal University, 453007, Xinxiang, People’s Republic of China;Henan Key Laboratory of Infrared Materials and Spectrum Measures and Applications, School of Physics, Henan Normal University, 453007, Xinxiang, People’s Republic of China;Shanghai Advanced Research Institute, Chinese Academy of Sciences, 201210, Shanghai, People’s Republic of China;State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, 430071, Wuhan, People’s Republic of China;

关键词: Donor-π-acceptor;    Conjugated polymers;    Charge transfer;    Exciton relaxation dynamics;   

DOI  :  10.1186/s11671-021-03507-0

来源: Springer

【 摘 要 】

Intramolecular exciton dissociation is critical for high efficient mobile charge carrier generations in organic solar cells. Yet despite much attention, the effects of π bridges on exciton dissociation dynamics in donor–π–acceptor (D-π-A) alternating conjugated polymers remain still unclear. Here, using a combination of femtosecond time-resolved transient absorption (TA) spectroscopy and steady-state spectroscopy, we track ultrafast intramolecular exciton relaxation dynamics in three D-π-A alternating conjugated polymers which were synthesized by Qin's group and named HSD-A, HSD-B, HSD-C. It is found that the addition of thiophene unit as π bridges will lead to the red shift of steady-state absorption spectrum. Importantly, we reveal the existence of a new intramolecular exciton dissociation pathway mediated by a bridge-specific charge transfer (CT′) state with the TA fingerprint peak at 1200 nm in π-bridged HSD-B and HSD-C. This CT′ state results in higher electron capture rates for HSD-B and HSD-C as compared to HSD-A. Depending on the proportion of CT′ state and nongeminate recombination are important step for the understanding of high power conversion efficiencies in HSD-B than in HSD-C. We propose that this bridge-specific exciton dissociation pathway plays an important role in ultrafast intramolecular exciton dissociation of organic photovoltaic material D-π-A alternating conjugated polymers.

【 授权许可】

CC BY