Atomic Layer Deposition Grown Nb-Doped SnO₂ Electron Transport Layers for High-Performance p–i–n Perovskite Devices

Perovskite solar devices in p–i–n architecture have attracted significant attention due to their long-term operational stability and compatibility for multijunction systems. Identifying a suitable electron transport layer (ETL), i.e., processed with a low thermal budget, scalable, highly conformal, uniform and with tunable optoelectrical properties, is a major research focus. Metal oxides produced by atomic layer deposition (ALD) have been revealed as promising candidates. Herein, we report the first application of SnO₂:Nb as an ETL in p–i–n architecture perovskite solar cells (PSCs) and minimodules (PSMs). The optoelectronic properties of SnO₂ were finely tuned by control of ALD process parameters and highly impacted the photovoltaic (PV) performances of the devices. Various SnO₂:Nb compositions were screened on small-area devices (0.09 cm²), and the optimal one outperformed the pristine SnO₂ reference (+2% absolute power conversion efficiency). The compatibility of the SnO₂:Nb ETL with large scale systems and the positive impacts of Nb doping on PV performances were confirmed by fabricating the PSM (active area of 4 cm²). Further investigation, including dark J–V curves, external and internal quantum efficiencies, steady-state and time-resolved photoluminescence, and structural and morphological characterizations were performed to reveal the Nb impact on the perovskite layer and its consequence on PV performance. The enhanced PV performances are mostly ascribed to better resistances (reduced series one and increased shunt), which are linked to SnO₂:Nb ETL electrical properties. Finally, PSC devices with SnO₂:Nb ETL showed comparable long-term stability as the reference one. PSMs incorporating optimal SnO₂:Nb ETL have +0.6% absolute efficiencies than their reference counterparts after 300 h under aging conditions recommended by ISOS-L3 protocol (1 sun, 85°, 50% relative humidity) assigned mostly to better charge transport. This strategy is applicable to other perovskite compositions, and these findings point out the potential of ALD-processed SnO₂-based ETL for efficient, scalable, and stable PSCs.