Associate Professor, National Institute of Technology, Oyama College, Japan

Biography: Dr. Takehito Kato is an associate professor in mechanical engineering in Oyama college of National Institute of Technology, Japan. He received his Ph. D in 2007 at Kyushu Institute of Technology, Japan. Then, he had been a researcher in Sumitomo Chemical Co., Ltd. during 2007-2012. His current research focuses on morphology control of organic-inorganic hybrid phase structure and energy conversion devices based on organic-inorganic hybrid materials. Especially, now, his research group is focusing on the medical photo sensor, the photovoltaic cell, the thermal electrical conversion device. He has published several international peer-reviewed journals and attended various national and international conferences exceed 100. Furthermore, he has published over 60 patent applications.

Speech Title: Highly efficient for fully printable organic-inorganic hybrid bulk heterojunction thin-film solar cells
Aims: Photovoltaic cells, which are expected to serve as a clean and renewable energy source, are among the most abundant technologies for energy on Earth besides hydropower and wind power. On the other hand, organic-inorganic hybrid thin-film solar cells constructed using polythiophene derivatives and metal alkoxides constitute promising and novel organic-inorganic hybrid devices. We have reported some organic- inorganic bulk heterojunction solar cells with several p-type semiconducting polymers and Ti-alkoxides for the photoactive layer. These solar cells involve low fabrication cost and use safe materials, but their conversion efficiency is not very high. One reason for this is that the phase-separated structure is not controlled adequately for utilization in exciton generation and diffusion, charge separation, and charge transportation. Therefore, we present a three-component layer as the photoactive layer using the phase-separation assistant material.

Methods: Organic-inorganic hybrid thin-film solar cells were fabricated by conventional method for organic thin-film solar cells. The solar cell structure consists of indium-doped tin oxide transparent conductive film (ITO glass), photoactive layer (p-type semiconducting polymer/TiOx/fullerene derivative as the phase separation assistant material), and organic electrode. The current density–voltage characteristics were measured using a direct-current voltage and a current source/monitor under illumination with AM 1.5G simulated solar light at 100 mW/cm² . The phase-separated structures of the photoactive layers were investigated by scanning electron microscopy.

Results and Conclusions: The three-component bulk heterojunction solar cell with the p-type semiconducting polymer/TiOx/fullerene derivative (1:1:1) structure as a photoactive layer exhibited higher current density than the conventional two- component solar cell. We will discuss this result and the phase separation structure of the photoactive layer at the conference.