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High-performance electron transport layer (ETL) anode generally needs to form a uniform dense layer with suitable conduction band position and good electron transport properties. The TiO2 photoanode is primarily applied as the ETL because it is low-cost, has diverse thin-film preparation methods and has good chemical stability. However, pure TiO2 is not an ideal ETL because it lacks several important criteria, such as low conductivity and conduction band mismatch with compositional-tailored perovskite. Thus, TiO2 is an inefficient photo-anode or ETL for high-performance perovskite devices. In this study, sulfur as dopant in the TiO2 photo-anode thin film is used to fabricate solid-state planar perovskite solar cells in relatively high humidity (40–50%). The deposited S-doped thin film improves the power conversion efficiency (PCE) of the device to 6.0%, with the un-doped TiO2 producing a PCE of 5.1% in the best device. Improvement in PCE is due to lower recombination and higher photocurrent density, resulting in 18% increase in PCE (5.1–6.0%).

Abstract High-performance perovskite solar cells have attracted increased attention for photovoltaic applications and potentially replacing the predecessor generations. Nevertheless, the stability issues and the lead content has always been among the major concerns that barriers perovskite solar cells from commercialization. This review presents the discussion towards the inherent instability of perovskite solar cells and the development towards replacing lead with discussion towards their performance and challenges. The degradation of perovskite active layer would release toxic substance into the environment. The development towards low-toxic, lead-free and efficient perovskite solar cells is the key for a sustainable solar energy generation with the application of perovskite solar cells.