Narrow bandgap molecular dyads Incorporating Y-series acceptor backbones for efficient single-molecular organic solar cells

The performance of organic solar cells (OSCs) is mainly related to the bulk heterojunction (BHJ) microstructure of specific active layer systems, which is often in a metastable state. A promising strategy to address the abovementioned shortcomings of BHJs is to develop single-component active layer materials. Owing to the single-component small molecule materials with defined chemical structures generally exhibit poor absorption spectra, herein we first introduced narrow bandgap Y-series acceptors into the molecular skeleton of single-component materials, and designed two molecular dyads, SM-Et-1Y and SM-Et-2Y. The optical bandgaps (\(E_{\rm{g}}^{{\rm{opt}}}{\rm{s}}\)) of the two dyads are 1.364 and 1.361 eV, respectively, which are much smaller than those of previously reported single-component molecules. Consequently, the SM-Et-2Y-based single-component OSCs (SCOSCs) showed a power conversion efficiency (PCE) of 5.07%, superior to SM-Et-1Y (2.53%), which is one of the highest PCEs reported for SCOSCs to date. Moreover, both SM-Et-1Y- and SM-Et-2Y-based devices exhibited excellent photo-stability, retaining over 90% of their initial performance after 250 h of continuous illumination. Our results provide a deeper understanding of the molecular backbone and a guiding principle for the rational design or selection of non-fullerene single-component materials with suitable donor/acceptor ratios.