Exploration of In₂S₃ as an Electron Transport Layer for All-Inorganic CsPbBr₃ Perovskite Solar Cells

In this paper, we demonstrate the fabrication of planar-based CsPbBr<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> perovskite solar cells with the use of $\mathrm{In}_{2} \mathrm{~S}_{3}$ as an electron transport layer (ETL) fabricated by chemical bath deposition. CsPbBr<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> films were fabricated by multi-step spin coating of PbBr<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> and CsBr ink, respectively, followed by annealing in air at $250^{\circ} \mathrm{C}$ for 30 min followed by deposition of a carbon-based electrode. The device showed an efficiency of $0.7 \%\left(J_{s c}=1.3 \mathrm{~mA} / \mathrm{cm}^{2}, \mathrm{~V}_{\mathrm{oc}}=1.165 \mathrm{~V} F \mathrm{FF}=47 \%\right.$), which was higher than that of the device without an ETL with an efficiency of $0.4 \%\left(J_{\mathrm{sc}}=1.9 \mathrm{~mA} / \mathrm{cm}^{2}, \mathrm{~V}_{\mathrm{oc}}=0.685 \mathrm{~V} \mathrm{FF}=\right.$ 32%). A relatively small grain sizes of the CsPbBr<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> film growth in the $\mathbf{I n}_{2} \mathrm{~S}_{3}$ layer ($\sim \mathbf{5 0 0} \mathbf{~ n m}$) was thought to be responsible for the relatively low efficiency of the device compared to that of using a conventional TiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> layer as the ETL layer.