Annealing-Insensitive, Alcohol-Processed MoO Hole Transport Layer for Universally Enabling High-Performance...

At present, most solution-processed molybdenum oxide (s-MoO) 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 MoO HTL that can universally enable high-performance conventional and inverted OSCs. The s-MoO HTL is spin-coated from the MoO nanoparticle dispersion in alcohol, where the MoO nanoparticles are synthesized by simple nonaqueous pyrolysis conversion of MoO₂(acac)₂. The MoO nanoparticles possess uniform and very small sizes of less than 5 nm and can be well dispersed in alcohol, so the s-MoO HTLs on ITO and active layer both show an overall uniform and smooth surface, suitable for conventional and inverted OSCs. In addition, the s-MoO HTL possesses decent optical transmittance and appropriate work function. Utilizing the s-MoO 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-MoO HTL could be annealing-insensitive and universal for conventional and inverted OSCs. Moreover, conventional and inverted OSCs with the s-MoO 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-MoO HTL show similarly excellent ambient stability compared to the e-MoO-based devices. In addition, the s-MoO HTL also shows a universal function in conventional and inverted OSCs with PBDB-T:ITIC and PM6:L8-BO active layers. Notably, the s-MoO-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 MoO HTL may be very promising for flexible and large-scale processing conventional/inverted OSCs.