Effects of Flexible Conjugation-Break Spacers of Non-Conjugated Polymer Acceptors on Photovoltaic and Mechanical Properties of All-Polymer Solar Cells
Qiaonan Chen, Yung Hee Han, Leandro R. Franco, Cleber F. N. Marchiori, Zewdneh Genene, C. Moysés Araújo, Jin‐Woo Lee, Tan Ngoc‐Lan Phan, Jingnan Wu, Donghong Yu, Dong Jun Kim, Taek‐Soo Kim, Lintao Hou, Bumjoon J. Kim, Ergang Wang
Abstract
All-polymer solar cells (all-PSCs) possess attractive merits including superior thermal stability and mechanical flexibility for large-area roll-to-roll processing. Introducing flexible conjugation-break spacers (FCBSs) into backbones of polymer donor (PD) or polymer acceptor (PA) has been demonstrated as an efficient approach to enhance both the photovoltaic (PV) and mechanical properties of the all-PSCs. However, length dependency of FCBS on certain all-PSC related properties has not been systematically explored. In this regard, we report a series of new non-conjugated PAs by incorporating FCBS with various lengths (2, 4, and 8 carbon atoms in thioalkyl segments). Unlike common studies on so-called side-chain engineering, where longer side chains would lead to better solubility of those resulting polymers, in this work, we observe that the solubilities and the resulting photovoltaic/mechanical properties are optimized by a proper FCBS length (i.e., C2) in PA named PYTS-C2. Its all-PSC achieves a high efficiency of 11.37%, and excellent mechanical robustness with a crack onset strain of 12.39%, significantly superior to those of the other PAs. These results firstly demonstrate the effects of FCBS lengths on the PV performance and mechanical properties of the all-PSCs, providing an effective strategy to fine-tune the structures of PAs for highly efficient and mechanically robust PSCs.