Stacking orientation mediation of pentacene and derivatives for high open-circuit voltage organic solar cells

• Main Authors: Chi-Ta Chou, 周啟達
• Other Authors: Yian Tai
• Format: Others
• Language: en_US
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/ajc756

博士 === 國立臺灣科技大學 === 化學工程系 === 100 === Molecular stacking orientation is one of the major factors for high performance in organic solar cells. Here, we study the open-circuit-voltage (VOC) of organic heterojunction photovoltaic cells based on pentacene and its derivatives. Two functionalized forms of pentacene- 6,13-dipheynl-pentacene (DP-Penta) and 6,13-Di-bipheynl-4-yl-pentacene (DB-Penta)– have been used for this study. Different molecular stacking orientations of the pentacene-derivatives have been identified by angle dependent near-edge X-ray absorption fine structure (NEXAFS) measurements. It’s concluded that pentacene molecules stand up on the PEDOT:PSS surface, while functionalized pentacene molecules lie down on the surface upon the modification of additional orthogonal phenyl rings. A significant increase of the VOC from 0.28 to 0.83 V has been observed when a conventional pentacene/C60 cell is replaced by the DB-penta/C60 cell. This result can be attributed to the fact that down-lying molecular stacking orientation of the functionalized pentacene induced a vacuum level (V. L.) shift, resulting in improved VOC of the devices. This approach has important implications for organic electronic devices that comprise multiple organic layers, and particularly for improving the power conversion efficiency of organic photovoltaic cells.