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Photoelectron spectroscopy was used to investigate poly(3-hexylthiophene) (P3HT), 6,6-phenyl C61 butyric acid methyl ester (PCBM), and their blends on various conductive substrates. The study shows a P3HT-rich layer at the top of the P3HT:PCBM blend films. The energy level alignment of the top P3HT changes with the work function of the substrate and the PCBM concentration at the bottom surface of the blend film. The results can be explained using the integer charge transfer model.
Xu et al. (Mon,) studied this question.