Promoting the photovoltaic performance and stability of organic solar cells by imidazole-doped PEDOT:PSS

Owing to the merits of solution processable, tunable electrical conductivity, high transparency and so forth, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) has been one of the most widely used hole transport layers (HTL) in organic solar cells (OSCs), particularly in conventional cell architectures. However, the inherent acid and hygroscopic nature as well as the relatively low conductivity of the as-prepared PEDOT:PSS, seriously attenuated the stability and efficiency of the corresponding devices. To address this issue, in this contribution, the mild organic base imidazole (IM) was introduced as dopant to neutralize the acidity and improve the conductivity of the as-prepared PEDOT:PSS. Using PTB7-Th:PC 71 BM as active layer, the OSCs devices based on imidazole treated PEDOT:PSS (PEDOT:PSS-IM) shows a best of 10.09%, which is much higher than that of the un-treated PEDOT:PSS-based devices. Moreover, the PEDOT:PSS-IM-based devices display much better stability. For comparison, devices using 1-methylimidazole (MIM)-doped PEDOT:PSS as hole transport layer (HTL) has been explored. However, an inferior PCE of 8.97% was obtained. These results indicate that the hydrogen bonding interactions between imidazole and PSS plays vital role in elevating the photovoltaic performance and stability of OSCs. Additionally, PEDOT:PSS-IM also displays enhanced performance in the case of other devices with different active layers, indicating a good university in OSCs.