17% Efficient Organic Solar Cells Based on Liquid Exfoliated WS₂ as a Replacement for PEDOT:PSS

The application of liquid-exfoliated 2D transition metal disulfides (TMDs) as the hole transport layers (HTLs) in nonfullerene-based organic solar cells is reported. It is shown that solution processing of few-layer WS₂ or MoS₂ suspensions directly onto transparent indium tin oxide (ITO) electrodes changes their work function without the need for any further treatment. HTLs comprising WS₂ are found to exhibit higher uniformity on ITO than those of MoS₂ and consistently yield solar cells with superior power conversion efficiency (PCE), improved fill factor (FF), enhanced short-circuit current (J_SC ), and lower series resistance than devices based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and MoS₂ . Cells based on the ternary bulk-heterojunction PBDB-T-2F:Y6:PC₇₁ BM with WS₂ as the HTL exhibit the highest PCE of 17%, with an FF of 78%, open-circuit voltage of 0.84 V, and a J_SC of 26 mA cm^-2 . Analysis of the cells' optical and carrier recombination characteristics indicates that the enhanced performance is most likely attributed to a combination of favorable photonic structure and reduced bimolecular recombination losses in WS₂ -based cells. The achieved PCE is the highest reported to date for organic solar cells comprised of 2D charge transport interlayers and highlights the potential of TMDs as inexpensive HTLs for high-efficiency organic photovoltaics.