Polyethylenimine Aqueous Solution: A Low-Cost and Environmentally Friendly Formulation to Produce Low-Work-Function Electrodes for Efficient Easy-to-Fabricate Organic Solar Cells

Polyethylenimine (PEI) has been widely used to produce low-work-function electrodes. Generally, PEI modification is prepared by spin coating from 2-methoxyethanol solution. In this work, we explore the method for PEI modification on indium tin oxide (ITO) by dipping the ITO sample into PEI aqueous solution for organic solar cells. The PEI prepared in this method could reduce the work function of ITO as effectively as PEI prepared by spin coating from 2-methoxyethanol solution. H2O as the processing solvent is more environmentally friendly and much cheaper compared to the 2-methoxyethanol solvent. The dipping method is also compatible with large-area samples. With low-work-function ITO treated by the dipping method, solar cells with a simple structure of glass/ITO/PEI(dipping)/P3HT:ICBA/PEDOT:PSS(vacuum-free processing) display a high open-circuit voltage of 0.86 ± 0.01, a high fill factor of 66 ± 2%, and power conversion efficiency of 4.4 ± 0.3% under 100 mW/cm(2) illumination.