Innovative Nb-Doped SnO₂ Electron Transport Layers Prepared by Atomic Layer Deposition for Enhanced Perovskite Solar Cells

Rapid advancements in perovskite solar cell (PSC) technology have highlighted the critical role of precise interface engineering in enhancing device stability and performance. Metal oxide-based electron transport layers (ETLs) prepared by atomic layer deposition (ALD) have emerged as promising candidates for improving PSC efficiency and stability. In this study, Nb-doped SnO2 (SnO2:Nb) thin films fabricated by ALD were employed as ETLs in n-i-p architecture PSCs. By leveraging the atomic-level control of ALD, the optoelectronic properties of SnO2:Nb thin films were finely tuned through controlled Nb doping, significantly influencing the photovoltaic (PV) performance of the devices in threshold behavior. PSCs incorporating SnO2:Nb thin film ETLs with low Nb atomic contents (≤0.2 at. %) exhibited improved performance, with an absolute increase in power conversion efficiency (PCE) of 0.93%, primarily due to increased Voc and Jsc values. Half-cell and extensive characterizations, including dark J–V curves, external and internal quantum efficiencies, impedance spectroscopy, and steady-state and time-resolved photoluminescence, were conducted to elucidate the effect of Nb doping. The perovskite layer was found to remain unaffected by ETL modification. The performance enhancement is attributed to the improved electrical properties of ETL thin films, leading to reduced series resistance and increased shunt resistance, as well as the reduction of interface defects, alteration of decay times, and favorable band alignments. These findings highlight the potential of ALD-processed SnO2-based ETLs for next-generation PSCs.