Researchers at Kanazawa University claim to have identified the main reason for the erosion of long-term efficiency in organic PV (OPV) devices.
They presented their findings in Factors contributing to degradation of organic photovoltaic cells, which was published on the ScienceDirect website. In their study, they describe the mechanism through which organic solar cells can be damaged by UV sunlight.
By using impedance spectroscopy and UV-VIS spectrophotometry, the scientists observed that the performance of an OPV device, under 100-h light irradiation, decreased by around 50%. They believe this degradation can be attributed to increased resistance of the organic semiconductor layer. The increase in resistance was caused by a decrease in the number of carriers, they said, suggesting that structural changes in the non-fullerene acceptor (EH-IDTBR) molecule are an important factor affecting degradation.
“Our alternating current (AC) impedance spectroscopic (IS) analysis of the device clearly showed a change in the resistance of the organic active layer under continuous light irradiation,” the researchers wrote.
The scientists added that they have not found a clear relationship between the change in the morphology of the organic layer and the decrease in device performance.
The structural change of the acceptor material associated with light irradiation, which is said to be the cause of cell performance degradation, was also measured by mass spectrometry, the research team said.
“Although UV light irradiation reduces device performance, this appears to be a separate effect from structural changes of the material and morphological changes of the active layer,” they concluded, while also specifying that influences other than the organic active layer should be considered in future research.