Intrinsically Stretchable Organic Photovoltaic Thin Films Enabled by Optimized Donor-Acceptor Pairing

The development of efficient stretchable organic photovoltaics (OPVs) poses a challenge that requires addressing the coupling of morphology and electronic structure in donor/acceptor blended thin films, which represents the interplay between mechanical deformation and photophysical performance. In this study, intrachain modification is employed to enhance the stretchability of conjugated polymers PTzBI-Si and P(NDI2OD-T2), which is a well-studied donor/acceptor combination in all-polymer solar cells. By introducing segments 1,2-di(thiophen-2-yl)ethene and 1,8-di(thiophen-2-yl)octane, the crack-onset strains of the polymer are significantly increased. This effect is achieved by randomizing the local intrachain conformation and tuning the crystalline packing and chain aggregation. The donor/acceptor pairing of the modified polymers is evaluated with their OPV performance, where the combination of PO-5:NV-10 shows well-balanced stretchability and performance. With the morphological optimization by the addition of the solvent additive dibenzyl ether, the PO-5:NV-10 thin film exhibits 1 order of magnitude increase in the crack-onset strain, surpassing 20%, along with a device efficiency of 8.45%, comparable to that of the reference blend. These findings highlight the importance of the optimal selection of donor/acceptor pairs in achieving intrinsically stretchable OPVs without compromising efficiency.