Direct Observation of Hole Accumulation in Polymer Solar Cells During Device Operation using Light-Induced Electron Spin Resonance

A clear correlation between the number of accumulated holes (N-spin) in poly(3-hexylthiophene) (P3HT) and the deterioration of the performance is observed in polymer solar cells under simulated solar irradiation. The sites of hole accumulation with deep trapping levels are formed at the interfaces between P3HT:[6,6]-phenyl C-61-butyric acid methyl ester (PCBM) and poly(3,4-ethylenedioxythiophene): poly(4-styrenesulfonate) (PEDOT:PSS) layers.