Asymmetric photocurrent extraction in semitransparent laminated flexible organic solar cells

Scalable production methods and low-cost materials with low embodied energy are key to success for organic solar cells. PEDOT(PSS) electrodes meet these criteria and allow for low-cost and all solution-processed solar cells. However, such devices are prone to shunting. In this work we introduce a roll-to-roll lamination method to construct semitransparent solar cells with a PEDOT(PSS) anode and an polyethyleneimine (PEI) modified PEDOT(PSS) cathode. We use the polymer:PCBM active layer coated on the electrodes as the lamination adhesive. Our lamination method efficiently eliminates any shunting. Extended exposure to ambient degrades the laminated devices, which manifests in a significantly reduced photocurrent extraction when the device is illuminated through the anode, despite the fact that the PEDOT(PSS) electrodes are optically equivalent. We show that degradation-induced electron traps lead to increased trap-assisted recombination at the anode side of the device. By limiting the exposure time to ambient during production, degradation is significantly reduced. We show that lamination using the active layer as the adhesive can result in device performance equal to that of conventional sequential coating. Printing solar cell: yield enhanced by laminating the active layerThe manufacturing yield of the flexible organic solar cells is enhanced with a new lamination method by solving the shunting problem due to conductive inks. A collaborative team led by Olle Inganas from Linkoping University, Sweden fabricates polymer: PCBM all-organic solar cells in ambient conditions using the active layer as the lamination adhesive. The team shows that reduced exposure to ambient is critical to achieve high device efficiency and suppress degradation. The degraded devices generate asymmetric photocurrent due to the electron traps in the active layer. The reported active layer lamination method not only solves the shunting problem in a number of different polymer: PCBM combinations, but also provides wide tenability and control of the composition and vertical phase separation of the active layer.