AVS 58th Annual International Symposium and Exhibition
    Energy Frontiers Focus Topic Thursday Sessions
       Session EN-ThP

Paper EN-ThP1
Development of Analysis System for Evaluating Carrier Lifetime in Organic Thin Film Solar Cell

Thursday, November 3, 2011, 6:00 pm, Room East Exhibit Hall

Session: Energy Frontiers Poster Session
Presenter: Kyohei Naito, KAST, Chuo Univ., Japan
Authors: K. Naito, KAST, Chuo Univ., Japan
M. Sakai, KAST, Japan
H. Takei, KAST, Japan
K. Nakata, KAST, Tokyo Univ. Sci., Japan
K. Katayama, Chuo University, Japan
K. Takagi, KAST, Japan
A. Fujishima, KAST, Tokyo Univ. Sci., Japan
Correspondent: Click to Email
Recently, photovoltaic cell is expected as new green technology replacing fossil fuel. Because of a next-generation photovoltaic cell with flexibility, portability and low cost, organic thin film solar cell (OTFSC) is currently the subject of great interest and intensive study. OTFSC is composed of organic electronic materials, which have differences in electron affinity and ionization energy, between two metallic conductive electrodes. The layer of the material with higher electron affinity and ionization potential is electron acceptor, and the other layer is electron donor. The hole-electron pairs (exciton) generated in either material, when OTFSC was photoinduced. When most of excitons reach the interface of the electron acceptor and electron donor, excitons break into carriers of electrons and holes efficiently. Electrons and holes move in the acceptor and donor, respectively. The carriers are collected by the electrode in contact with each layer. In the latest report, OTFSC has exceeded 8 percent of conversion efficiency. However, it was difficult to increase the area of OTFSC with high conversion efficiency. For instance, the conversion efficiency depended on the layer defects, which was caused by contamination of dust and H2O, oxidation and inhomogeneous coating. The defects influenced the carrier lifetime in OTFSC. Hence, the inspection technique, which was evaluated in two dimensions XY, was required to measure the carrier lifetime. The present inspection technique (Laser beam induced current method) had to contact electrodes with electric wires and pass an electric current through OTFSC. Because the carrier lifetime was measured by the decay of electric current, the value was influenced by every interface of circuitry in OTFSC. Therefore, it was necessary to detect the pure carrier lifetime in the organic semi conductivity layer. In this study, to investigate the pure carrier lifetime in the OTFSC, we developed the analysis system employing micro wave photoconductivity decay (μPCD). The carrier life time was discussed from the viewpoints of electrochemistry and quantum mechanics.