Resonance Raman Spectroscopic- and Photocurrent Imaging of Polythiophene/Fullerene Solar Cells

Resonance Raman-photocurrent imaging (RRPI) is introduced to spatially map the 'morphology-dependent polymer aggregation state to local photocurrent generation efficiency in poly-(3-hexylthiophene) (P3HT) and [6,15]phenyl-C-61-butyric acid methyl ester (PCBM) blend thin film photovoltaic devices. The C=C symmetric stretching mode of P3HT is decomposed into contributions from aggregated (I-C=C(agg), similar to 1450 cm(-1)) and unaggregated (I-C=C(un), similar to 1470 cm(-1)) chains, and the ratios of their integrated intensities (I-C=C(agg),I-C=C(un), R) is used as a reporter for the local P3HT aggregation state. Maps of R values and photocurrents are generated for both as-cast and annealed P3HT/PCBM devices that permit direct spatial correlations between the P3HTaggregation state and local photocurrent generation efficiency. Regions of increased P3HTaggregation are observed at both P3HT/PCBM interfaces and in P3HT-rich areas that result in decreased photocurrent generation. Voltage-dependent RRPI studies are also performed at several applied bias levels that reveal distinct changes in photocurrents due to morphology-dependent charge mobility characteristics.