Rapid and low temperature processing of mesoporous TiO2 for perovskite solar cells on flexible and rigid substrates

Perovskite solar cells (PSCs) have recently attracted the attention of the scientific community because of the rapid advances in their development. Most of the state-of-the-art devices contain mesoporous titanium dioxide (TiO2) as an electron transport layer. The drawback of such TiO2 layers is that it often needs high temperature sintering at 450-500 degrees C for 30 min, which slows down the fabrication process and is clearly not compatible with future roll-to-roll (R2R) manufacturing. The aim of this study was to develop low temperature and rapid curing techniques for mesoporous TiO2 thin films, which are compatible with R2R processing and heat-sensitive plastic substrates for PSCs. Several alternative annealing techniques were tested on rigid and flexible substrates, such as UV-ozone (UV/O-3) treatment, oxygen plasma treatment (O-2 plasma) and Intense Pulsed Light (IPL) sintering and compared to conventional thermal annealing. After each treatment, the mesoporous layers were characterized using Raman spectroscopy, UV-vis spectroscopy, thermogravimetric analysis and scanning electron microscopy. Low temperature sintering techniques were specifically optimized for the mesoporous TiO2 layers and were adapted for the fabrication of PSCs. Sintering process and solar cells manufacturing were optimized for two different device architectures on glass as well as on polyethylene naphthalate (PEN) substrates. Moreover, the maximum temperature of the mesoporous TiO2 layer during the IPL curing process was simulated to better understand the curing process. By employing IPL curing, the processing time for the mesoporous TiO2 layer can be reduced from 30 min to a few seconds without significant loss in the device performance. In particular stabilized PCE of 16% and 12% were obtained using IPL on glass and PEN substrates respectively. This processing route paves the way for future low temperature R2R processing of mesoscopic PSC on plastic substrates.