Rapid and Low-Temperature Processing of Mesoporous and Nanocrystalline TiO₂ Film Using Microwave Irradiation

Nanoporous (np)-TiO₂ films have multiple applications, including dye-sensitized and perovskite solar cells. However, preparation of np-TiO₂ films on transparent conductive oxide-coated surfaces (e.g., fluorine doped tin oxide (FTO)) requires high-temperature sintering (450-500 °C) for at least 30-60 min in a conventional oven. Here, we introduce a novel technique to rapidly produce np-TiO₂ films on FTO-coated glass substrates via microwave (MW) irradiation. np-TiO₂ films were sintered on FTO-glass substrates in less than 10 min at temperatures less than 260 °C using an optimized MW irradiation program and a simple MW attenuation technique. Significantly, cracking of FTO-coated glass substrates was avoided during MW irradiation, which was a limiting problem in previous studies. MW-developed films were evaluated with UV-vis absorption spectrophotometry, Raman spectroscopy, X-ray diffraction, and atomic force microscopy, with MW-developed films (>4 min) producing essentially identical characteristics as conventionally annealed films. Dye-sensitized solar cells (DSSCs) fabricated with MW-developed films (8 min) demonstrated an overall power conversion efficiency of 7.16% as compared to 7.04% for conventionally-fabricated DSSCs. This rapid and low-temperature sintering technique saves time and energy and may also pave the way for deposition of np-TiO₂ films on plastic-based substrates.