fabrication of uniform vertically-aligned titanium dioxide nanorods (tio 2 nRs) was achieved by hydrothermal growth on a fluorine-doped tin oxide (FTO) glass substrate. The substrate was coated by a tio 2 seed layer composed of titanium (IV) butoxide (TBO) as a precursor in an HCl solution. To reduce the amount of toxic substances used in this work, a minimal amount of HCl was used. On a larger scale, this method would require less precursor and therefore be a cost-savings. The aim of the present work is to achieve high crystalline orientations of tio 2 nRs for low quantities of both tBo precursor and Hcl solutions. Results showed that the 0.7% TBO TiO 2 NRs after 1.5 h of hydrothermal treatment exhibited the optimal crystalline orientation along [001] while the (002) plane is the dominant facet. The results demonstrate high transmittance of visible light and well-formed crystalline structures that offer a fast electron pathway along the length of the tio 2 NRs with less grain boundaries. Lastly, TiO 2 nRs and their growth mechanism are discussed. This work offers a promising hydrothermal method for growing wellaligned tio 2 single-crystal NRs that can be employed in solar cell applications. There is a growing demand for new materials to use in applications that meet today's energy and environmental challenges. In particular, wide band gap semiconductors, using very promising materials, are demonstrating impressive properties for example, high electron mobility, large band gaps and reasonably good conductivity. Among semiconducting wide band-gap materials, titanium dioxide (TiO 2) and zinc oxide (ZnO) are alternative materials used as electron transporting layers with suitable energy levels relative to Perovskite solar cells (PSC). Due to the superior electron transfer capability of each material, which is a crucial factor for PSC performance, many approaches have been found allowing TiO 2 and ZnO to be used together to enhance the overall power conversion efficiency (PCE) of PSCs. Even though ZnO layers exhibit higher electron mobility compared to TiO 2 , ZnO-based PSCs exhibit poor stability, which is a serious problem. If a Perovskite layer is created from a composition of methyl ammonium + (CH NH) 3 3 and lead triiodide − (PbI) 3 deposited on a ZnO layer, it can easily decompose during thermal treatment. However, there is less of this thermal decomposition for Perovskite and TiO 2 interfaces. TiO 2 has an acidic surface while a ZnO surface shows basic properties with high adsorption of positive charges 1. When Perovskite is exposed on a ZnO layer, a deprotonation reaction with + CH NH 3 3 occurs which could break the ionic interaction between + CH NH 3 3 and − PbI 3 and as a result, it can obstruct the crystal formation of the Perovskite 2. TiO 2 becomes the better choice and overwhelmingly interesting for its fundamental aspects and applications as well as the main motivation of this work. Moreover, TiO 2 is an ideal candidate for the large-scale manufacture of chemicals due to its stability, non-toxicity an...

The development of metal oxide‐based electron transport layers in perovskite solar cells (PSCs) has received intensive research interest for achieving high‐efficiency PSCs. Herein, TiO2 nanorods (TiO2 NRs) are grown onTiO2 seed layers coated on fluorine‐doped tin oxide (FTO) glass substrate by using a hydrothermal method and then are utilized as the electronic transport layer in PSCs. The main concern, after hydrothermal growth of TiO2 NRs, is that their crystallinity can be improved by a sequential high‐temperature treatment at 450 °C. In addition to high‐temperature annealing, a low‐temperature treatment with boiling water, which is expected to clean the surface of the TiO2 NRs, is developed. In this contribution, the champion PSCs are those based on TiO2 NRs where boiling water treatment achieves a maximum power conversion efficiency (PCE) of 15.50%, whereas a PCE of 12.91% is obtained from PSCs based on TiO2 NRs with high‐temperature annealing. The remarkable ease of using a water‐assisted process offers an efficient approach to the removal of residuals adsorbed on the surface and circumvents the disadvantage of a thermal annealing method resulting in high‐production costs. This low‐temperature treatment can be used to improve TiO2 films in flexible PSCs.

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