Synthesis and photovoltaic properties of the copolymers based on 3-ethylrhodanine side group

• Four copolymers with BDT and 3-ethylrhodanine side group were synthesized.
• 3-Ethylrhodanine was introduced into the copolymers as side group.
• The PSC based on the copolymers showed a high Voc of 0.94 V.

Four conjugated copolymers (PBDT-TRD, PBDT-3TRD, PBDT-TTRD, and PBDT-3TTRD) based on 3-ethylrhodanine in the side chains have been designed and synthesized. The effects of the conjugated π-bridge and 3-ethylrhodanine unit on absorption spectra, energy levels, and photovoltaic properties of the copolymers have been investigated. These copolymers exhibit good thermal stabilities, broad absorption spectra, and deep highest occupied molecular orbital (HOMO) energy levels. The polymer solar cells have been fabricated by using these copolymers as the donors and [6,6]-phenylC61-butyric acid methyl ester (PC61BM) as the acceptor. Among them, the devices based on PBDT-TRD and PBDT-TTRD demonstrated preferable power conversion efficiencies of 3.35% and 3.18% with high open-circuit voltages of 0.94 V and 0.85 V, respectively.

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