Intrinsically Stretchable and Non-Halogenated Solvent Processed Polymer Solar Cells Enabled by Hydrophilic Spacer-Incorporated Polymers

Blends of polymer donors (P(D)s) and small molecule acceptors (SMAs) have afforded highly efficient polymer solar cells (PSCs). However, most of the efficient PSCs are processed using toxic halogenated solvents, and they are mechanically fragile. Here, a new series of P(D)s by incorporating a hydrophilic oligo(ethylene glycol) flexible spacer (OEG-FS) is developed, and efficient PSCs with a high power conversion efficiency (PCE) of 17.74% processed by a non-halogenated solvent are demonstrated. Importantly, the incorporation of these OEG-FSs into the P(D)s significantly increases the mechanical robustness and ductility of resulting PSCs, making them suitable for application as stretchable devices. The OEG-FS alleviates excessive backbone rigidity of the P(D)s while enhancing their pre-aggregation in the non-halogenated solvent. In addition, the OEG-FS in the P(D)s enhances P-D-SMA interfacial interactions and improves blend morphology, resulting in efficient charge generation and mechanical stress dissipation. The resulting PSCs demonstrate a superior PCE (17.74%) and high crack-onset strain (COS = 10.50%), outperforming the PSCs without OEG (PCE = 15.64% and COS = 2.99%). Importantly, intrinsically stretchable (IS) PSCs containing the P-D featuring OEG-FS exhibit a high PCE (12.05%) and stretchability (maintaining 80% of the initial PCE after 22% strain), demonstrating their viability for wearable applications.