Low-Temperature Processing Methods for Tin Oxide as Electron Transporting Layer in Scalable Perovskite Solar Cells

Perovskite solar cell (PSC) technology experiences a remarkably rapid growth toward commercialization with certified efficiency of over 25%, along with the outstanding breakthrough in the development of SnO2. Owing to the wide bandgap, high electron mobility, chemical stability, and low photocatalytic activity, SnO2 has been the rising star to serve as electron transporting layer (ETL). More importantly, the low-temperature fabrication process (<200 degrees C) enables SnO2 a promising candidate for the industry, making it compatible with the plastic substrates and large-scale production, which is crucial for the flexible and scalable devices fabrication. In this review, the processing methods (solution-based, vacuum-based, and vapor-based deposition) of low-temperature SnO2 (LT-SnO2) and the pros and cons of them with a focus on their scalability are discussed. Additionally, the morphologies of obtained LT-SnO2 are investigated to guide the design and performance improvement of devices. The modification strategies to reduce undesired nonradiative recombination and passivate the defects in the bulk or at the interface of LT-SnO2, influencing the quality of perovskite films, together with the efficiency and stability of cells are summarized. This review is a comprehensive overview of the studies on low-temperature SnO2 ETL and provides detailed instructions for scalable PSCs.