Efficient Organic Solar Cells with Extremely High Open-Circuit Voltages and Low Voltage Losses by Suppressing Nonradiative Recombination Losses

One of the most important factors that limits the efficiencies of bulk-heterojunction organic solar cells (OSCs) is the modest open-circuit voltage (V-oc) due to their large voltage loss (V-loss) caused by significant nonradiative recombination loss. To boost the performance of OSCs toward their theoretical limit, developing high-performance donor: acceptor systems featuring low V-loss with suppressed nonradiative recombination losses (<0.30 V) is desired. Herein, high performance OSCs based on a polymer donor benzodithiophene-difluorobenzoxadiazole-2-decyltetradecyl (BDT-ffBX-DT) and perylenediimide-based acceptors (PDI dimer with spirofluorene linker (SFPDI), PDI4, and PDI6) are reported which offer a high power conversion efficiency (PCE) of 7.5%, 56% external quantum efficiency associated with very high V-oc (>1.10 V) and low V-loss (<0.60 V). A high V-oc up to 1.23 V is achieved, which is among the highest values reported for OSCs with a PCE beyond 6%, to date. These attractive results are benefit from the suppressed nonradiative recombination voltage loss, which is as low as 0.20 V. This value is the lowest value for OSCs so far and is comparable to high performance crystalline silicon and perovskite solar cells. These results show that OSCs have the potential to achieve comparable V-oc and voltage loss as inorganic photovoltaic technologies.