Beneficial effects of amino acid-functionalized graphene nanosheets incorporated in the photoanode material of dye-sensitized solar cells: A practical and theoretical study

Abstract In this research, covalently functionalized graphene oxide (GO) with some biocompatible amino acids were incorporated to the TiO 2 film and employed as the photoanodes of dye-sensitized solar cells (DSSCs). Electrochemical analysis of the amino acids-functionalized graphene oxide (AFGs) confirmed that the attached amino acids could be acted as a reducing agent of the GO. The photovoltaic performance of the assembled DSSCs under illumination of simulated AM 1.5 sunlight (100 mW cm −2 ) showed an enhancement of about 4.1 and 1.8 fold for the solar cell assembled with the tyrosine-functionalized GO in relation to the control solar cells constructed with GO-TiO 2 composite and blank TiO 2 film, respectively. These results were in accordance with electron life time and transport time resulted from the open circuit voltage decay (OCVD), electrochemical impedance spectroscopy (EIS) and intensity modulated photocurrent spectroscopy (IMPS) analysis. The density functional theory (DFT) calculations exhibited a proper spacial arrangement for the tyrosine-GO structure that could improve electron transfer between the adjucent GO sheets. Density of electronic states (DOS) exhibited a gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels for the simulated AFG structures. This effect could facilitate the light adsorption process in near-IR region.