At present, most solution-processed molybdenum oxide (s-MoO x ) 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 x HTL that can universally enable high-performance conventional and inverted OSCs. The s-MoO x HTL is spin-coated from the MoO x nanoparticle dispersion in alcohol, where the MoO x nanoparticles are synthesized by simple nonaqueous pyrolysis conversion of MoO2(acac)2. The MoO x nanoparticles possess uniform and very small sizes of less than 5 nm and can be well dispersed in alcohol, so the s-MoO x 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 x HTL possesses decent optical transmittance and appropriate work function. Utilizing the s-MoO x 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 x HTL could be annealing-insensitive and universal for conventional and inverted OSCs. Moreover, conventional and inverted OSCs with the s-MoO x 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 x HTL show similarly excellent ambient stability compared to the e-MoO x -based devices. In addition, the s-MoO x 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 x -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 x HTL may be very promising for flexible and large-scale processing conventional/inverted OSCs.

2D Ti 3 C 2 T x MXene, possessing facile preparation, high electrical conductivity, flexibility, and solution processability, shows good application potential for enhancing device performance of perovskite solar cells (PVSCs). In this study, tetrabutylammonium bromide functionalized Ti 3 C 2 T x (TBAB-Ti 3 C 2 T x ) is developed as cathode buffer layer (CBL) to regulate the PCBM/Ag cathode interfacial property for the first time. By virtue of the charge transfer from TBAB to Ti 3 C 2 T x demonstrated by electron paramagnetic resonance and density functional theory, the TBAB-Ti 3 C 2 T x CBL with high electrical conductivity exhibits significantly reduced work function of 3.9 eV, which enables optimization of energy level alignment and enhancement of charge extraction. Moreover, the TBAB-Ti 3 C 2 T x CBL can effectively inhibit the migration of iodine ions from perovskite layer to Ag cathode, which synergistically suppresses defect states and reduce charge recombination. Consequently, utilizing MAPbI 3 perovskite without post-treatment, the TBAB-Ti 3 C 2 T x based device exhibits a dramatically improved power conversion efficiency of 21.65% with significantly improved operational stability, which is one of the best efficiencies reported for the devices based on MAPbI 3 /PCBM with different CBLs. These results indicate that TBAB-Ti 3 C 2 T x shall be a promising CBL for high-performance inverted PVSCs and inspire the further applications of quaternary ammonium functionalized MXenes in PVSCs.