Influence of Thermal Annealing on PCDTBT:PCBM Composition Profiles

摘要

A variety of measurement techniques including photothermal deflection spectroscopy (PDS), auger electron spectroscopy (AES), (sub–bandgap) external quantum efficiency (EQE), and impedance spectroscopy are applied to poly[N-900-hepta-decanyl-2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole (PCDTBT)/[6,6]-phenyl C71 butyric acid methyl ester (PC71BM) films and devices to probe the stability under thermal annealing. Upon annealing, solar cell performance is drastically decreased for temperatures higher than 140 °C. Detailed investigation indicate changes in polymer:fullerene interactions resulting in the formation of a polymer wetting layer upon annealing at temperatures higher than 140 °C. Upon device completion this wetting layer is located close to the metal electrode and therefore leads to an increase in recombination and a decrease in charge carrier extraction, providing an explanation for the reduced fill factor (FF) and power conversion efficiency (PCE).