SnO₂ nanorod arrays with tailored area density as efficient electron transport layers for perovskite solar cells

Tin dioxide (SnO₂) is regarded as an effective electron transport material for attaining high-performance perovskite solar cells (PSCs). Herein, vertically aligned SnO₂ nanorod arrays are grown directly on fluorine-doped tin oxide (FTO) substrates in an acidic solution via hydrothermal method, where the area density of the nanorod arrays is tailored by varying the precursor concentration. Particularly, the mean diameters of the nanorods increase from 15 to 25 nm and the corresponding area densities decrease from 660 to 460 μm⁻² with increasing the concentration of tin(IV) chloride pentahydrate. X-ray diffraction and X-ray photoelectron spectroscopy measurements reveal that the nanorod arrays are pure tetragonal rutile SnO₂ with a high degree of crystallinity. Mixed perovskites of (FAPbI₃)_0.85(MAPbBr₃)_0.15 are infiltrated into these SnO₂ nanorod arrays, and the perovskite solar cells show an enhanced photovoltaic performance as compared to the nanoparticle counterpart. Perovskite solar cells based on SnO₂ nanorod arrays with the optimized area density exhibit the best power conversion efficiency of 15.46% which is attributed to an accelerated electron transport and a decreased recombination rate at SnO₂/perovskite interface.