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Fine Tuning of Open-Circuit Voltage by Chlorination in Thieno[3,4‑b]thiophene–Benzodithiophene Terpolymers toward Enhanced Solar Energy Conversion

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Version 3 2017-06-29, 14:22
Version 2 2017-06-28, 13:52
Version 1 2017-06-27, 14:50
journal contribution
posted on 2017-06-27, 00:00 authored by Shiwei Qu, Huan Wang, Daize Mo, Pengjie Chao, Zhen Yang, Longji Li, Leilei Tian, Wei Chen, Feng He
A new family of thieno­[3,4-b]­thiophene–benzodithiophene terpolymers (PBTClx) have been designed and synthesized, in which the chlorine/fluorine content has been adjusted and optimized. As the content of chlorine is increased in polymers, the twist angle between the donor and acceptor is increased, which leads to a diminishment in the planarity and conjugation. As a result, the UV–vis absorption is continuous blue-shifted, and the band gap increases from 1.57 to 2.04 eV when the chlorinated moieties increased from 0 to 100%. The highest occupied molecular orbital (HOMO) levels of those polymers are decreased by increasing the content of chlorinated moiety, which opens a window to constantly modify the Voc values and eventually meets a balance point for optimized solar energy conversion. The highest power conversion efficiency of 8.31% is obtained by using PBTCl25 as the donor and PC71BM as the acceptor in polymer solar cells (PSCs), in which the Voc increased from 0.79 to 0.82 V after 25% chlorinated monomer involved in copolymerization. Herein, the chlorine replacement could be a good method to further pump the solar conversion by increasing the open circuit voltage without reducing other factors of the polymer solar cells.

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