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

Comprehensive Summary 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 NiO x , CoO x and VO x , with suitable work functions have attracted numerous research attention recently. In this work, more abundant and easily accessible oxygenated salt, vanadyl sulfate (VOSO 4 ) has been demonstrated to be excellent choice as HTL for OSCs. The VOSO 4 ‐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 VOSO 4 ‐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, VOSO 4 ‐based OSCs exhibit improved stability when stored in the N 2 filled glove box. After being stored for 600 h, VOSO 4 ‐based device can retain 89% of its initial efficiency. Notably, VOSO 4 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.