High-phase purity two-dimensional perovskites with 17.3% efficiency enabled by interface engineering of hole transport layer

State-of-the-art p-i-n-based 3D perovskite solar cells (PSCs) use nickel oxide (NiOX) as an efficient hole transport layer (HTL), achieving efficiencies >22%. However, translating this to phase-pure 2D perovskites has been unsuccessful. Here, we report 2D phase-pure Ruddlesden-Popper BA(2)MA(3)Pb(4)I(13) perovskites with 17.3% efficiency enabled by doping the NiOX with Li. Our results show that progressively increasing the doping concentration transforms the photoresistor behavior to a typical diode curve, with an increase in the average efficiency from 2.53% to 16.03% with a high open-circuit voltage of 1.22 V. Analysis reveals that Li doping of NiOX significantly improves the morphology, crystallinity, and orientation of 2D perovskite films and also affords a superior band alignment, facilitating efficient charge extraction. Finally, we demonstrate that 2D PSCs with Li-doped NiOX exhibit excellent photostability, with T-99 = 400 h at 1 sun and T-90 of 100 h at 5 suns measured at relative humidity of 60% +/- 5% without the need for external thermal management.