Achieving efficient flexible perovskite solar cells with room-temperature processed tungsten oxide electron transport layer

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For flexible perovskite solar cells, achieving high power conversion efficiency by using a room-temperature technology to fabricate a compact electron transport layer is one of the best options. Here, we develop an annealing-free, dopant-free, and amorphous tungsten oxide as electron transport layer by vacuum evaporation for flexible perovskite solar cells. The compact amorphous tungsten oxide electron transport layer with different thicknesses (0–50 nm) was directly deposited on flexible PEN/ITO substrate. A model of the improvement mechanism is proposed to understand how the thickness tailoring simultaneously enhances the crystallization and relaxes the trade-off between interface recombination and charge transfer. By optimizing the amorphous tungsten oxide thickness, the high homogeneous, uniform, and dense electron transport layer with a thickness of 30 nm is found to not only decrease the pinhole of the perovskite layer, but also enhance charge transport with reducing resistance. Furthermore, the mechanical bending stability revealed that, the fabricated perovskite solar cells show stable power conversion efficiency up to more than 1000 bending cycles. The room-temperature processed fabrication enables the amorphous tungsten oxide to become a potential electron transport layer candidate for the large-scale flexible perovskite solar cells, which becomes compatible with practical roll-to-roll solar cells manufacturing.