Dimerized small molecular acceptors: Regulation of dimer conformation realizes binary organic solar cells with highly comprehensive performance

Dimerized small-molecular-acceptors (DSMA)-based organic solar cells have gained much progress but insufficient flexibility of the rigid DSMAs limits application in wearable electronics. By regulating dimer conformation, a series of DSMAs (2BOHD-T, 2BOHD-TCxT (x = 4, 6)) are synthesized through microwave-assist-reaction. Conformation evolution from 2-dimension planarity to 3-dimension architecture evoked by linkage engineering from rigidity to flexibility precisely controls the electronic structures, intermolecular interactions, film-forming processes, and flexibility of DSMAs. The rigid terminal-linked 2BOHD-T performs best in small-area devices with efficiency of 17.68%. The 3-dimensional flexible terminal-linked 2BOHD-TC4T achieves a record efficiency of 16.50% with a notable VOC of 0.980 V among the reported flexible DSMAs. 2BOHD-TC4T-based large-area printing device obtains the best efficiency (14.53%) among these acceptors. Furthermore, PM6:2BOHD-TC4T not only improves thermal stability close to the all-polymer system but also achieves an excellent crack onset strain, producing the large-area flexible device with excellent bending tolerance. An updated evaluation parameter, efficiency-stretchability-thermal stability-factor (ESSTF), is proposed. 2BOHD-TC4T-based device yields the highest ESSTF, demonstrating the most balanced large-area device efficiency, thermal stability, and mechanical robustness.