Optimization of Atomic Layer Deposition Process of Tin Oxide Thin Films for Near-Infrared-Transparent Halide Perovskite Solar Cells

Transparent electrodes, typically sputtered transparent conducting oxides (TCOs), are employed in tandem and bifacial perovskite solar cell (PSC) configurations for light transmission. The sputtering process of TCOs’ deposition damages the underlying perovskite and organic charge transporting layers. Tin oxide (SnOx) thin film deposited via atomic layer deposition (ALD) is being used as a buffer layer to prevent damages from high-energy particles and ultraviolet (UV) light during the sputtering process. This study focuses on the optimization of atomic layer deposition (ALD) process parameters for the deposition of SnOx thin films at low temperatures. This work investigates the effects of deposition temperature, precursor exposure, and purge times on the growth behaviors. Structural, optical, and compositional properties of ALD-SnOx thin films are studied in detail as a function of growth parameters. ALD-SnOx (20 nm), deposited via varied recipes, provides films with high average transmittance (>94.8%; 350–1200 nm), varied refractive index (1.78–1.95), negligible extinction coefficient, varied composition of SnOx (x = 1.7–1.95), smooth surfaces (roughness of 0.18–0.28 nm), and high mass density (>5.6 g/cm3), which are suitable to be employed as functional layers in near-infrared (NIR)-transparent PSCs. Further, we apply the optimized SnOx film in NIR-transparent PSCs as a buffer layer for sputtered TCOs.