Molecular Oriented Charge Accumulation in High-Efficiency Polymer Solar Cells as Revealed by Operando Spin Analysis.

A low band-gap polymer, PTB7-Th, is one of the typical p-type semiconductors among the next-generation solar-cell materials that have achieved power conversion efficiencies of over 10%. However, the internal deterioration mechanism of high-efficiency polymer solar cells such as PTB7-Th-based cells is still an open issue and has been extensively studied. Here, we report a study with operando electron spin resonance (ESR) spectroscopy for PTB7-Th polymer solar cells with an n-type semiconductor PCBM to clarify the internal deterioration mechanism at a molecular level.