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Efficient Planar Perovskite Solar Cells with Entire Low-Temperature Processes via Brookite TiO2 Nanoparticle Electron Transport Layer

Electron transport layer (ETL) is well known as a crucial factor that affects power conversion efficiency (PCE) of perovskite solar cells (PSCs). Low temperature process on ETL has been highly considered for the future of low cost and roll to roll process in mass production of PSCs industrialization. Herein, we demonstrate the low-temperature (<180 °C) processes of pure phase, single crystalline brookite TiO2 nanoparticle (BK TiO2 NPs) layer as an ETL of PSCs, followed by different concentrations of TiCl4 treatment (20mM, 40mM, 60mM and 80mM). By using BK TiO2 NPs with the low temperature process (<180 °C), our device exhibited the highest power conversion efficiency of 15.49% in planar-type PSCs, indicating that the BK TiO2 NPs layer is a new candidate of ETL that can be fabricated in low temperature processes. The optimized TiCl4 concentration is 40mM for the surface treatment of BK TiO2 NPs, which results in the enhancement of PCE, reproducibility and the supression of hysteresis. Probably, the 40mM of TiCl4 treatment improves the interface between the perovskite and BK TiO2 NPs layers and promotes the efficient charge extraction. Thus, the present work is expected to provide an important technology to realize the low-cost planar PSCs produced in entire low-temperature processes.