Organic solar cells, which have attracted considerable interest over the last few years as low-cost, simply-processed alternatives for harvesting the solar energy, have interesting nanoscale properties; a thorough understanding of which is currently lacking. Although there has been a considerable amount of work focused on improving the overall device efficiency, important issues related to nanoscale morphology on exciton dissociation and charge transport, effect of grain boundaries and fine interfaces, and contact related phenomena are mostly unexplored. Conductive-tip atomic force microscopy (c-AFM) is a powerful technique that can be utilized to simultaneously gain some understanding of the local electronic response of blended n-and p-type molecules and their surface morphology when prepared on transparent conducting electrodes. Here, we present transport data and local photocurrent maps and images of polythiophene/PCBM organic films collected with our c-AFM in an inert atmosphere, in the presence of excitation with monochromatic light, with the goal of correlating life-size device efficiency with nano-morphology and local response of the active organic film. We have also used a streamlined technique for fabrication of stencil masks with sub-micron features on a suspended SiN membrane to be used as a shadow mask for evaporating nanoscale top contacts onto the organic layer. These top contacts can then be imaged and analyzed locally by the AFM tip, and the photocurrent voltage or impedance measurements can be performed on the length scales dictated by the size of the contacts. We compare the results of these measurements with those obtained from larger mm-sized devices.
Proceedings Title: Nanoscale Photoresponse in Blended Organic Photovoltaics
Conference Dates: August 16-20, 2009
Conference Location: Washington, DC
Conference Title: American Chemical Society, PMSE division
Pub Type: Conferences
solar cells, organic electronics, photovoltaics