Interface Engineering with Nb2CT x MXene Electron Transport Layer for Defect-Controlled Lead-Free MASnI3 Perovskite Solar Cells

Abstract

Lead-free tin-based perovskite solar cells offer environmentally sustainable alternatives to conventional lead-based perovskite solar cells but suffer from high defect densities and poor interfacial charge selectivity, which limit their efficiency and stability. This work presents a comprehensive numerical study of Nb2CTx MXene as an electron transport layer in methylammonium tin iodide (MASnI3) perovskite devices using SCAPS-1D simulation. Two planar n-i-p architectures are investigated: a full transport layer stack FTO/Nb2CTx/MASnI3/NiO/Ni (HTL-based) and a simplified FTO/Nb2CTx/MASnI3/Ni (HTL-free) structure. Under optimized conditions, the HTL-based device reaches a power conversion efficiency of 26.93% with Voc = 1.03 V, Jsc = 31.04 mA cm–2, and FF = 84.01%, while the HTL-free device attains a PCE of 26.53% with Voc = 1.02 V, Jsc = 31.98 mA cm–2, and FF = 81.33%. Parametric sweeps indicate that MASnI3 thicknesses of 600–800 nm for the HTL-based device, up to 1200 nm for the HTL-free device, and Nb2CTx thicknesses of 100–200 nm, together with a Nb2CTx donor density of 1016 cm–3 and a bulk defect density of 1015 cm–3, are suitable for high performance. The HTL-free configuration is more sensitive to Nb2CTx bulk and interface defects, which suggests stricter requirements for ETL quality and processing. Interface defect densities below 1013 cm–2, especially at the MASnI3/Nb2CTx interface, are favorable for suppressing recombination. Both architectures achieve external quantum efficiency above 95% in the visible range and show impedance spectra consistent with efficient carrier extraction. Overall, the simulations indicate that Nb2CTx can serve as a tunable ETL for lead-free tin perovskites and offer practical guidelines for designing MASnI3 perovskite solar cells with efficiency above 26% in both HTL-based and HTL-free layouts.