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Solution-Processed Silver Electrode for Inverted Organic Solar Cell Based on Easily Deposited Hole Transporting Layer onto Hydrophobic Active Layer

For reducing the production costs, decreasing the fabrication time and for practical applications used in roll-to-roll process for inverted organic solar cells (IOSCs), silver (Ag) back-electrode have been deposited from silver paste solution at room temperature using simple, cheap and easy manual spray method, with completely avoiding the use of thermal evaporation system for solar cell preparation. In addition, a layer of poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) as a hole transporting layer have been deposited from an aqueous solution onto hydrophobic active layer without any chemical additives or additional treatments. For optimizing the Ag film, to be used as a back electrode in the IOSCs, series resistance of the indium tin oxide (ITO)/PEDOT:PSS/Ag device was measured at different compositions of silver paste dispersed in ethanol, different annealing temperatures and different silver paste amounts sprayed onto PEDOT:PSS layer. The dilution process of silver paste with ethanol is practical to reduce its commercial cost and to decrease its viscosity to be easily sprayed using spray gun for application in large scale production with avoiding solidification and fast curing at room temperature. Using the present method, the Ag electrode has been efficiently sprayed on the top of organic solar cells with low electrical resistance, large thickness and good hardness against crashes. We found that, the high thickness of both PEDOT:PSS layer and Ag electrode deposited on the top of solar cell active layer prevent and suppress oxygen penetration towards P3HT:PCBM active layer. Therefore, the optimized solar cell revealed good air stability, compared to their counterparts in other literatures, under ambient atmosphere with approximately 86% retention of their original conversion efficiency after 154 days. Our results indicate that the solution-processed Ag back-electrode using easy method has a potential to be used in roll-to-roll processed organic solar cells and other optoelectronic applications.