Facile Approach for Efficient Non-Fullerene-Based Binary and Ternary Organic Solar Cells Using Hydrated Vanadium Pentoxide as a Hole Transport Layer

Although the power conversion efficiency (PCE) of single-junction organic solar cells (OSCs) has exceeded more than 19%, the biggest obstacle to the commercial application of OSCs is the low device stability. Herein, this work reports the development of hydrated vanadium pentoxide (HVO) as a hole transport layer (HTL) with outstanding hole-extracting capabilities by a simple synthesis process and its use in the non-fullerene-acceptor-based binary and ternary OSCs. OSCs based on PM6:BTP-eC9 using an indium tin oxide/hydrated vanadium pentoxide (ITO/HVO) anode exhibit a maximum PCE of 13.33%, which is higher than ITO/poly(3,4-ethylene dioxythiophene):(polystyrene sulfonate) (PEDOT:PSS) (12.09%). Additionally, ternary (with an active layer of PM6:BTP-eC9:PC71BM) devices were also fabricated to analyze the impact of HVO HTL and achieved a PCE of 14.34%. The higher PCE is found to originate from the much higher work function (WF) of ITO/HVO than ITO/PEDOT:PSS. Furthermore, to replace a sophisticated thermal evaporation technique with a solution-processed, we fabricated inverted devices with HVO instead of control MoO3 HTL. The highest occupied molecular orbital (HOMO) energy level of HVO is nearly equal to MoO3, and the device based on HVO attributed a PCE of 7.47%, which is higher than MoO3 (6.70%)-based devices. This work provides a low-cost, highly efficient, and solution-processed HTL material for OSCs with long-term air stability.