Benzotriazole-Based Acceptor and Donors, Coupled with Chlorination, Achieve a High <i>V</i>_OC of 1.24 V and an Efficiency of 10.5% in Fullerene-Free Organic Solar Cells

Abstract

Herein, a simple “Same-A-Strategy” (SAS), constructing p-type and n-type photovoltaic materials with the same electron-accepting (A) unit of benzotriazole, is adopted to initially control the energy offsets. Then, chlorine atoms are introduced into the conjugated side chain of the benzo[1,2-b:4,5-b′]dithiophene (BDT) donor unit of the p-type polymer to fine-tune the optoelectronic properties. The chlorinated polymer J52-Cl, blended with a non-fullerene small molecule acceptor BTA3, yields the very small energy offsets (ΔEHOMO = 0.10 eV, ΔELUMO = 0.28 eV) and the decreased nonradiative recombination loss of 0.24 eV. Benefiting from the strong molecular aggregation, ordered molecular orientation, and fine film morphology, J52-Cl:BTA3 device delivers balanced carriers mobilities and also suppressed charge recombination losses. Consequently, the obtained device yields a very high open-circuit voltage (VOC) of 1.24 V, a short-circuit current (JSC) of 13.16 mA cm–2, and a fill factor of 66.62%, giving rise to a promising power conversion efficiency (PCE) of 10.5%, which is a large breakthrough for organic solar cells with high VOC beyond 1.20 V. Our results provide a rare opportunity to break through the limitation of the problematic trade-off between energy loss and PCE and show a great potential for the application in tandem solar cells.