Halide Perovskite Solar Cells Using Monocrystalline TiO2 Nanorod Arrays as Electron Transport Layers: Impact of Morphology

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  • This is the first report of a 17.6 % champion efficiency solar cell architecture comprising monocrystalline TiO2 nanorods (TNRs) coupled with perovskite, and formed using facile solution processing without non-routine surface conditioning. Vertically oriented TNR ensembles are desirable as electron transporting layers (ETLs) in halide perovskite solar cells (HPSCs) because of potential advantages such as vectorial electron percolation pathways to balance the longer hole diffusion lengths in certain halide perovskite semiconductors, ease of incorporating nanophotonic enhancements, and optimization between a high contact surface area for charge transfer (good) vs. high interfacial recombination (bad). These advantages arise from the tunable morphology of hydrothermally grown rutile TNRs, which is a strong function of the conditions of growth. Fluorescence lifetime imaging microscopy (FLIM) of the HPSCs demonstrated a stronger quenching of the perovskite photoluminescence when using TNRs as compared to mesoporous TiO2 thin films of similar thickness and planar TiO2 ETLs. Such a high charge separation efficiency in TNR-based HPSCs is due the large interfacial contact area between the ETL and perovskite along with the ease of pore filling of the TNR ETL by the perovskite. At the same time, the low surface free electron density in hydrothermally grown single crystal rutile TNRs suppressed interfacial recombination between the electrons in the TNR ETL and photogenerated holes in the perovskite. The optimal ETL morphology in this study was found to consist of an array of TNRs ~ 300 nm in length and ~ 40 nm in width. This work highlights the potential of TNR ETLs to achieve high performance solution-processed HPSCs.

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    Attribution-NonCommercial 4.0 International