Low-Temperature Plasma-Assisted Atomic-Layer-Deposited SnO2 as an Electron Transport Layer in Planar Perovskite Solar Cells

In this work, we present an extensive characterization of plasma-assisted atomic-layer-deposited SnO2 layers, with the aim of identifying key material properties of SnO2 to serve as an efficient electron transport layer in perovskite solar cells (PSCs). Electrically resistive SnO2 films are fabricated at 50 degrees C, while a SnO2 film with a low electrical resistivity of 1.8 x 10(-3) Omega cm, a carrier density of 9.6 x 10(19) cm(-3), and a high mobility of 36.0 cm(2)/V s is deposited at 200 degrees C. Ultraviolet photoelectron spectroscopy indicates a conduction band offset of similar to 0.69 eV at the 50 degrees C SnO2/Cs-0.05(MA(0.17)FA(0.83))(0.95)Pb-(I2.7Br0.3) interface. In contrast, a negligible conduction band offset is found between the 200 degrees C SnO2 and the perovskite. Surprisingly, comparable initial power conversion efficiencies (PCEs) of 17.5 and 17.8% are demonstrated for the champion cells using 15 nm thick SnO2 deposited at 50 and 200 degrees C, respectively. The latter gains in fill factor but loses in open-circuit voltage. Markedly, PSCs using the 200 degrees C compact SnO2 retain their initial performance at the maximum power point over 16 h under continuous one-sun illumination in inert atmosphere. Instead, the cell with the 50 degrees C SnO2 shows a decrease in PCE of approximately 50%.