Reactive DC Sputtered TiO₂ Electron Transport Layers for Cadmium‐Free Sb₂Se₃ Solar Cells

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.