Nd:YAG pulsed laser production of reduced-graphene oxide as hole transporting layer in polymer solar cells and the influences of solvent type

Graphene oxide (GO) was reduced using 532 nm Nd:YAG pulsed laser irradiation (unfocused, 10 Hz repetition rate, 0.3 J/cm(2)) in different solvents including water, ethanol and formic acid. The obtained reduced GOs (r-GOs) were employed as hole transporting layers (HTLs) in fabrication of polymer solar cells (PSCs). The changes in the chemical composition, phase purity, optical properties, level of defects, sheet resistance (R-sh), charge transfer resistance (R-ct) and morphology of r-GOs were systematically investigated using Fourier transform infrared spectroscopy, x-ray diffraction, UV-Vis and Raman spectroscopy, four-point probe, electrochemical impedance spectroscopy and atomic force microscopy. Results revealed that laser reduction of GO in formic acid led to formation of r-GOs with superior physicochemical and electrochemical characteristics, implying higher hole scavenging ability of formic acid compared to water and ethanol. The r-GOs prepared in formic acid appeared to have the lowest R-sh, R-ct and surface roughness. This was attributed to the higher elimination of oxygenated functional groups in formic acid, confirmed by results obtained from physicochemical characterization of the prepared samples. Comparing the photovoltaic parameters of PSCs prepared based on r-GOs as HTL revealed that the r-GO sample produced in formic acid can act as a better HTL in P3HT:PCBM-based PSCs. This cell exhibited the highest short circuit current density (10.15 mA) and power conversion efficiency (4.02%), which was about 22% higher than that achieved for the reference PSC prepared using PEDOT:PSS as HTL. Results suggest that pulsed laser production can be considered as a promising method to produce r-GOs possessing appropriate characteristics as HTL in PSCs.