Spectroscopic Imaging of Molecular Photovoltaic Materials: New Insights into Charge Generation and Transport

Understanding structure-function relationships of charge generation and transport processes is a crucial challenge to achieve commercially viable molecular-based, thin film photovoltaic devices. Our research uses resonance Raman spectroscopic imaging to study the fundamental processes of charge generation and transport in functioning devices by spatially correlating their efficacies to local chemical and morphological structure. The advantage of this approach over other physical tools is that it provides detailed (sub-micron) information—in a totally non-invasive manner—about local variations in chemical structure parametrically with electronic energy. We then use relationships between Raman intensities and fundamental parameters of charge transfer (reorganization energies) to map how these critical parameters vary with different film morphologies arising from different film processing conditions. The results are then expected to help bridge the gap in the understanding of charge transfer processes from single molecule to bulk levels and help guide the rational design of new photovoltaic materials processing strategies.