Synthesis of oriented TiO2 nanocones with fast charge transfer for perovskite solar cells

One-dimensional (1D) rutile TiO2 nanostructures on fluorine-doped tin oxide (FTO) substrates are interesting building blocks of solar cells, and they have been traditionally prepared under highly acidic conditions. In this article, a green, facile hydrothermal approach was exploited to grow oriented rutile TiO2 nanocones on FTO under nearly neutral conditions in a high-control way. XRD, SEM, TEM, HRTEM, and Raman spectroscopy were used to characterize the nanocones, showing rutile phase with single-crystalline structure, and the length of nanocones can be tailored in the range of 700 similar to 1400 nm by varying the reaction durations. As building blocks of CH3NH3PbI3-based perovskite solar cells, 11.9% power conversion efficiency was achieved for the TiO2 nanocone devices, which is significantly superior to the state-of-the-art efficiency for other 1D nanostructure counterparts (similar to 10% for TiO2 nanorods and 11% for ZnO nanorods, respectively). It was further revealed by time-resolved photoluminescence spectroscopy (TRPL) that electron transfer from CH3NH3PbI3 to TiO2 nanocones is significantly faster than to TiO2 nanorods, an important factor to suppress charge recombination and improve device performance. These characteristics make nanocones to be a promising candidate as electron transport materials for photovoltaic devices. (C) 2014 Elsevier Ltd. All rights reserved.