Development of a Novel method in Area of Organic Photovoltaic Cell for improved Conversion Efficiency, for Realization of Light-Weight and Flexible Photovoltaic Sheets
Organic photovoltaic cell (OPC) technology holds a promising future over its silicon solar cell counterpart, for its capability in creating light-weight and flexible solar cell sheets. Furthermore, OPCs can be manufactured without any needs for vacuum or high temperature environment; however the conversion efficiency of OPC is hovering between 7 to 8 percent hampering its practical use. Factors for such low efficiency include, a limited wavelength range of optical absorption, resulting in inactivity of OPCs to near-infrared light, which holds around 40% of total solar radiation energy, and extremely short lifetime of photo-exited states, which results in large energy loss before the photoelectric conversion occurs. These issues are due to inherent nature of organic semiconductors, where the excitonic states are strongly confined to individual molecules. Based on this limitation, group of researchers at AIST has developed a new type of OPC that is based on optical absorption, occurs during the charge transfer between different molecules.
According to this finding, since the wavelength region of the charge transfer optical absorption varies depending on the combination of the molecules, it is possible to use near-infrared light for photovoltaic conversion. Based on this method, researchers have been able to fabricate and test a prototype photovoltaic device using molecular compound semiconductor consisting of electron-donor and electron-acceptor molecules, and molecular conductor materials as the highly efficient electron and hole-ejecting electrodes. AIST is working toward development of a multi-layered photovoltaic cell based on charge-transfer optical absorption for manufacturing highly efficient OPCs.