Predictive analysis of organic semiconductor photodegradation by FTIR spectroscopy with multivariate analysis

Organic semiconductors (OSCs) serve as the essential elements of emerging next-generation optoelectronic devices. These devices continue to experience advances in overall efficiency, but their long-term implementation is challenged by complex and often poorly understood degradation processes that can involve not only the OSC active component but also contacts and charge carrier transport layers. Better tools are needed to characterize chemical and photochemical degradation of these components in operando. Here, attenuated total reflectance-FTIR (ATR-FTIR) spectroscopy combined with multivariate analysis is demonstrated as a diagnostic tool for monitoring degradation of thin films of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7), an active layer material used in organic photovoltaics, as a model high-performance OSC. Multivariate analysis of the resulting FTIR spectral data is shown to be effective at identifying pristine (not degraded) versus degraded samples with high accuracy in accelerated photodegradation experiments. These results highlight the potential of practical diagnostic applications of multivariate analysis to assessment of OSC degradation.