Effect of Buffer Layers on Stability of Polymer-Based Organic Solar Cells

The long-term performance stability of organic solar cells (OSCs), as well as their high power conversion efficiency, is necessary for their practical use. For polymer-based OSCs, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is conventionally introduced as a buffer layer. However, there is concern that PEDOT:PSS, which is highly hygroscopic and acidic, accelerates the degradation of OSCs by oxidizing certain components of the OSCs. In this study, we compared the stabilities of three types of cell containing different buffer layers (PEDOT:PSS, molybdenum oxide, and no buffer layer). The OSC with the PEDOT:PSS layer was degraded very rapidly, while the other OSCs were degraded slowly. In addition, we observed that the oxidation of the aluminum electrode occurred at the aluminum/photovoltaic layer interface. These results suggest that PEDOT:PSS accelerates the oxidation of the aluminum electrodes of OSCs and reduces their efficiency. We conclude that the introduction of the PEDOT:PSS layer, despite producing a high "initial" efficiency, is not the best strategy to improve the OSC stability.