Electron Donor-Acceptor Nano-Domains in Bulk Heterojunctions of Organic Solar Cell Active Layers - Cross Sectional Scanning Tunneling Microscopy and Spectroscopy

Bulk heterojunctions in organic photovoltaic solar cell (OPVC) active layer are believed to be the ideal quasi-random nano-structures for high solar cell performance. It is also known that the OPVC efficiency strongly depends on the synthesis conditions, such as annealing temperatures, electron donor-acceptor compositions, thickness, electric field etc. In this research, the electron donor-acceptor nano-domain textures and sizes are studied by cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/S). By varying different synthesis parameters, we visualized drastic evolution of the nano-domain dimensions and textures. Correlations between these nano-domains to the solar cell efficiency will be established as the next step in near future. In this work, poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) are used as the model OPVC active layer materials.