Low-Temperature\nPlasma-Assisted Atomic-Layer-Deposited\nSnO₂ as an Electron Transport Layer in Planar Perovskite\nSolar Cells

Abstract

In this work, we\npresent an extensive characterization of plasma-assisted\natomic-layer-deposited SnO₂ layers, with the aim of identifying\nkey material properties of SnO₂ to serve as an efficient\nelectron transport layer in perovskite solar cells (PSCs). Electrically\nresistive SnO₂ films are fabricated at 50 °C, while\na SnO₂ film with a low electrical resistivity of 1.8 ×\n10^–3 Ω cm, a carrier density of 9.6 ×\n10¹⁹ cm^–3, and a high mobility of 36.0\ncm²/V s is deposited at 200 °C. Ultraviolet photoelectron\nspectroscopy indicates a conduction band offset of ∼0.69 eV\nat the 50 °C SnO₂/Cs_0.05(MA_0.17FA_0.83)_0.95Pb­(I_2.7Br_0.3) interface. In contrast, a negligible conduction band offset is\nfound between the 200 °C SnO₂ and the perovskite.\nSurprisingly, comparable initial power conversion efficiencies (PCEs)\nof 17.5 and 17.8% are demonstrated for the champion cells using 15\nnm thick SnO₂ deposited at 50 and 200 °C, respectively.\nThe latter gains in fill factor but loses in open-circuit voltage.\nMarkedly, PSCs using the 200 °C compact SnO₂ retain\ntheir initial performance at the maximum power point over 16 h under\ncontinuous one-sun illumination in inert atmosphere. Instead, the\ncell with the 50 °C SnO₂ shows a decrease in PCE of\napproximately 50%.