Vanadyl Sulfate Based Hole-Transporting Layer Enables Efficient Organic Solar Cells

It remains an urgent task to develop alternative hole-transporting layer (HTL) materials beyond commonly used PEDOT:PSS to increase the shelf-life of organic solar cells (OSCs). Inorganic metal oxide type materials, such as NiOx, CoOx and VOx, with suitable work functions have attracted numerous research attention recently. In this work, more abundant and easily accessible oxygenated salt, vanadyl sulfate (VOSO4) has been demonstrated to be excellent choice as HTL for OSCs. The VOSO4-based HTL can be readily processed by spin-coating from the precursor solution with subsequent thermal annealing and UVO treatment. As a consequence, a high power conversion efficiency (PCE) of 18.72% can be achieved for PM8:L8-BO based OSCs with the VOSO4-based HTL. High transmittance, smooth film surface, suitable energy level and high conductivity were revealed to contribute to the high OSC performance. More importantly, compared to device with PEDOT:PSS, VOSO4-based OSCs exhibit improved stability when stored in the N-2 filled glove box. After being stored for 600 h, VOSO4-based device can retain 89% of its initial efficiency. Notably, VOSO4 can be used as general HTL in PM6:BTP-BO-4Cl and PM6:IT-4F based OSCs, yielding high PCEs of 17.87% and 13.85%, respectively.