Annealing-Insensitive, Alcohol-Processed MoO_x Hole Transport Layer for Universally Enabling High-Performance Conventional and Inverted Organic Solar Cells

At present, most solution-processed molybdenum oxide (s-MoOx) hole transport layers (HTLs) are still mainly used in conventional organic solar cells (OSCs) but unsuitable for inverted OSCs. Herein, we demonstrate for the first time an annealing-insensitive, alcohol-processed MoOx HTL that can universally enable high-performance conventional and inverted OSCs. The s-MoOx HTL is spin-coated from the MoOx nanoparticle dispersion in alcohol, where the MoOx nanoparticles are synthesized by simple nonaqueous pyrolysis conversion of MoO2(acac)2. The MoOx nanoparticles possess uniform and very small sizes of less than 5 nm and can be well dispersed in alcohol, so the s-MoOx HTLs on ITO and active layer both show an overall uniform and smooth surface, suitable for conventional and inverted OSCs. In addition, the s-MoOx HTL possesses decent optical transmittance and appropriate work function. Utilizing the s-MoOx HTL annealed between room temperature and 110 °C and PM6:Y6 active layer, the conventional OSCs show an excellent power conversion efficiency (PCE) of 16.64–17.09% and the inverted OSCs also show an excellent PCE of 15.74–16.28%, which indicate that the s-MoOx HTL could be annealing-insensitive and universal for conventional and inverted OSCs. Moreover, conventional and inverted OSCs with the s-MoOx HTLs annealed at 80 °C both exhibit optimal PCEs of 17.09 and 16.28%, respectively, which are separately superior than that of the PEDOT:PSS-based conventional OSCs (16.94%) and the thermally evaporated MoO3 (e-MoO3)-based inverted OSCs (16.03%). Under light soaking and storage aging in air, the unencapsulated inverted OSCs based on the s-MoOx HTL show similarly excellent ambient stability compared to the e-MoOx-based devices. In addition, the s-MoOx HTL also shows a universal function in conventional and inverted OSCs with PBDB-T:ITIC and PM6:L8-BO active layers. Notably, the s-MoOx-based conventional and inverted OSCs with the PM6:L8-BO active layer exhibit very excellent PCEs of 18.21 and 17.12%, respectively, which are slightly higher than those of the corresponding PEDOT:PSS-based device (18.17%) and e-MoO3-based device (17.00%). The annealing-insensitive, alcohol-processed MoOx HTL may be very promising for flexible and large-scale processing conventional/inverted OSCs.