Energy Level Tuning of Non-Fullerene Acceptors in Organic Solar Cells (original) (raw)

The use of non-fullerene acceptors in organic photovoltaic devices could lead to enhanced efficiencies due to increased open-circuit voltages (VOC) and improved absorption of solar light. Here we systematically investigate planar heterojunction devices comprising peripherally substituted subphthalocyanines as acceptor, and correlate device performance with heterojunction energetics. Due to a balance between VOC and photocurrent, tuning of the interface energy gap is necessary to optimize power conversion efficiency in these devices. In addition, we explore the role of the charge transport layers in the device architecture. It is found that non-fullerene acceptors require adjusted buffer layers with aligned electron transport levels to enable efficient charge extraction, while the insertion of an exciton blocking layer at the anode interface further boosts photocurrent generation. These adjustments result in a planar heterojunction OPV device with 6.9% efficiency and a VOC above 1 V.