Chemical degradation mechanisms of organic photovoltaics studied by TOF-SIMS and isotopic labeling

The degradation mechanisms of conjugated polymer materials used in organic photovoltaic cells were studied. To elucidate the parts of the degradation mechanisms induced by molecular oxygen, isotopic labeling was employed in conjunction with time-of-flight secondary ion mass spectrometry (TOF-SIMS). Devices that were kept in the dark were compared with devices that had been subjected to illumination under simulated sunlight. It was found that molecular oxygen diffuses into the device causing oxygen-containing species to be generated throughout the active layers. The isotopic labeling combined with TOF-SIMS depth profiling and imaging allowed mapping of the oxidation processes by measuring the vertical and lateral distribution of oxygen-containing species. The exact pinpointing of the parts of the device that are susceptible to oxidation allows for a mechanism to be proposed that partly explains the device failure manifested in the insufficient life times of the organic photovoltaics.