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

Abstract

<h2>Summary</h2> 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, <b>G17</b> and <b>G19</b>, were designed and synthesized. Interestingly, the <b>G17</b>-containing sp³-carbon π-bridge features an amorphous orientation, whereas the silicon-substituted <b>G19</b> exhibits an extremely ordered edge-on orientation. When doped into D18-Cl:Y6 host system, the <b>G19</b>-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 <b>G17</b>-based ternary device only delivers a relatively low PCE of 17.13%. Correspondingly, flexible OSCs based on the <b>G19</b> 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.