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:PC 71 BM) 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 MoO 3 HTL. The highest occupied molecular orbital (HOMO) energy level of HVO is nearly equal to MoO 3, and the device based on HVO attributed a PCE of 7.47%, which is higher than MoO 3 (6.70%)-based devices. This work provides a low-cost, highly efficient, and solution-processed HTL material for OSCs with long-term air stability.