Reactive DC Sputtered TiO<sub>2</sub> Electron Transport Layers for Cadmium‐Free Sb<sub>2</sub>Se<sub>3</sub> Solar Cells
Christopher H. Don, Thomas P. Shalvey, Daniya A. Sindi, Bradley Francis Lewis, Jack E. N. Swallow, Leon Bowen, Daniel Félix Fernandes, Tomáš Kubart, Deepnarayan Biswas, P. Thakur, Tien‐Lin Lee, Jonathan D. Major
Abstract
Abstract The evolution of Sb 2 Se 3 heterojunction devices away from CdS electron transport layers (ETL) to wide bandgap metal oxide alternatives is a critical target in the development of this emerging photovoltaic material. Metal oxide ETL/Sb 2 Se 3 device performance has historically been limited by relatively low fill factors, despite offering clear advantages with regards to photocurrent collection. In this study, TiO 2 ETLs are fabricated via direct current reactive sputtering and tested in complete Sb 2 Se 3 devices. A strong correlation between TiO 2 ETL processing conditions and the Sb 2 Se 3 solar cell device response under forward bias conditions is observed and optimized. Numerical device models support experimental evidence of a spike‐like conduction band offset, which can be mediated, provided a sufficiently high conductivity and low interfacial defect density can be achieved in the TiO 2 ETL. Ultimately, a SnO 2 :F/TiO 2 /Sb 2 Se 3 /P3HT/Au device with the reactively sputtered TiO 2 ETL delivers an 8.12% power conversion efficiency ( η ), the highest TiO 2 /Sb 2 Se 3 device reported to‐date. This is achieved by a substantial reduction in series resistance, driven by improved crystallinity of the reactively sputtered anatase‐TiO 2 ETL, whilst maintaining almost maximum current collection for this device architecture.