Ternary organic solar cells with a selenophene-containing donor guest achieve a high efficiency of 18.41%.

Small-molecule (SM) donor based ternary organic solar cells (OSCs) have drawn increasing attention owing to the remarkable photovoltaic performances achieved recently. In this study, a chlorinated benzodithiophene core and selenophene-containing π bridge based SM donor, namely CBTSeHR, was used as an SM donor guest to fabricate ternary OSCs owing to its favorable optoelectronic properties. CBTSeHR exhibits a good complementary absorption band and matched energy levels with the prevailing polymer donors and SM nonfullerene acceptors (NFAs), which is beneficial to light harvesting and charge transport. In addition, the incorporation of CBTSeHR could modulate the micro morphology and endow the ternary blend with more favorable phase separation size. Accordingly, the as cast ternary device prepared by introducing CBTSeHR into the D18:CH-6F host system exhibits an excellent power conversion efficiency (PCE) of 17.33%, which is even higher than that of the optimal binary host device (17.08%). After thermal annealing (TA) treatment, an outstanding PCE value of 18.41% with a high V_oc of 0.901 V, FF of 0.767, and J_sc of 26.64 mA cm⁻² was achieved, demonstrating the great success of SM donor based ternary OSCs. [ABSTRACT FROM AUTHOR]