Polymer donors with hydrophilic side-chains enabling efficient and thermally-stable polymer solar cells by non-halogenated solvent processing
Soodeok Seo, Jun‐Young Park, Jin Su Park, Seungjin Lee, Do‐Yeong Choi, Yun‐Hi Kim, Bumjoon J. Kim
Abstract
Polymer solar cells (PSCs) with high power conversion efficiency (PCE) and environment-friendly fabrication are the main requirements enabling their production in industrial scale. While the use of non-halogenated solvent processing is inevitable for the PSC fabrication, it significantly reduces the processability of polymer donors (<i>P</i><sub>DS</sub>) and small-molecule acceptors (SMAs). This often results in unoptimized blend morphology and limits the device performance. To address this issue, hydrophilic oligoethylene glycol (OEG) side-chains are introduced into a <i>P</i><sub>D</sub> (2EG) to enhance the molecular compatibility between the <i>P</i><sub>D</sub> and L8-BO SMA. The 2EG <i>P</i><sub>D</sub> induces higher crystallinity and alleviates phase separation with the SMA compared to the reference <i>P</i><sub>D</sub> (PM7) with hydrocarbon side-chains. Consequently, the 2EG-based PSCs exhibit a higher PCE (15.8%) than the PM7-based PSCs (PCE = 14.4%) in the <i>ortho</i>-xylene based processing. Importantly, benefitted from the reduced phase separation and increased crystallinity of 2EG <i>P</i><sub>DS</sub>, the 2EG-based PSCs show enhanced thermal stability (84% of initial PCE after 120 h heating) compared to that of the PM7-based PSCs (60% of initial PCE after 120 h heating). This study demonstrates the potential of OEG side-chain-incorporated materials in developing efficient, stable, and eco-friendly PSCs.