Influence of a novel fluorosurfactant modified PEDOT:PSS hole transport layer on the performance of inverted organic solar cells

Under ambient conditions the long term stability of non-encapsulated organic solar cells with conventional device architecture is lower than the technical lifetime of devices with an inverted configuration. The removal of the interface between the ITO (indium tin oxide) layer and the acidic PEDOT:PSS layer along with the substitution of a low work function metal electrode with a high work function metal electrode in the inverted device configuration renders relatively higher stability in these devices. However, one of the main inherent difficulties involving the fabrication of devices with such inverted architecture is the wettability of the hydrophilic PEDOT:PSS onto the photoactive layer such as the P3HT:PCBM blend which is hydrophobic in nature. To overcome this, we have used a novel fluorosurfactant, Capstone (R) Dupont (TM) FS-31 (CFS-31), as a substitute to the conventional Zonyl FS-300 as an additive to PEDOT: PSS. A smooth and uniform PEDOT: PSS layer was coated onto the P3HT:PCBM blend layer by addition of CFS-31 alone without any further treatments. Using this surfactant, an efficiency of 3.1% and a stable device performance (up to 400 hours) under ambient conditions without encapsulation have been achieved.