Small-molecular donor guest achieves rigid 18.5% and flexible 15.9% efficiency organic photovoltaic via fine-tuning microstructure morphology

Summary Incorporation of crystalline small molecule into host binary systems to finely tune film morphology is demonstrated to be an effective method to improve photovoltaic performance for organic solar cells (OSCs). In this work, two small molecular donors with similar chemical structures, G17 and G19, were designed and synthesized. Interestingly, the G17-containing sp3-carbon π-bridge features an amorphous orientation, whereas the silicon-substituted G19 exhibits an extremely ordered edge-on orientation. When doped into D18-Cl:Y6 host system, the G19-based ternary device exhibits a largely improved power conversion efficiency (PCE) of 18.53%, which is among the highest PCEs for OSCs. By contrast, the G17-based ternary device only delivers a relatively low PCE of 17.13%. Correspondingly, flexible OSCs based on the G19 ternary active layer also give an excellent PCE of 15.9%. These results highlight that incorporating highly ordered molecular donor can be an effective method to construct highly efficient OSCs.