[13a-A303-1~8] 13.8 Optical properties and light-emitting devices

△ [13a-A303-3] Crystallization of organic-inorganic hybrid perovskite polycrystalline films with low defect density at low-temperature by microwave pulse irradiation

〇Tomoki Furuhashi¹, Shuntaro Tsubaki¹, Swee Sien Lim², Marcello Righetto², Mingjie Li², Tze Chien Sum², Yuji Wada¹ (1.Tokyo Tech, 2.Nanyang Tech. Univ.)

Keywords:perovskite, microwave, solar cell

Organic-inorganic hybrid perovskite solar cell has attracted attention because of its easy fabrication method and high-power conversion efficiency, which achieved 25.2 % as the maximum. Compared to it, the efficiency of the silicon solar cells, which is widespread in the world, is 27.6 %. So, improvement in efficiency is needed. In order to improve the efficiency, fabrication of perovskite thin film with good crystallinity is widely discussed. Especially, defects are the factor of decreasing efficiency. Carriers, which is generated by irradiation of light, are trapped into defects. The trapped carriers at defects cause recombination of themselves to decrease efficiency, and degradation of perovskite thin film to decrease the stability. Therefore, it is expected that efficiency increases by fabricating perovskite thin film with low defect density. In the previous research, Xing et al. reported the generation of a large amount of defects is caused by decreasing of CH₃NH₃I during annealing process of CH₃NH₃PbI₃ thin films. In general, defect density tends to increase at high temperatures.
In this work, I introduced microwave pulse irradiation in the annealing process of MAPbI₃ thin film. By irradiation of microwave, the FTO layer and TiO₂/FTO interface are heated selectively and locally by the interaction between microwave and free electrons in FTO and interfacial dipoles at TiO₂/FTO interface. In addition, I used the microwave as a pulse mode. When irradiating microwaves, FTO is heated to get locally high temperatures. Then crystallization of MAPbI₃ happens from the bottom of the MAPbI₃ layer. When the irradiation is stopped, rapid thermal diffusion happens to protect the perovskite layer against degradation and vaporization.