Abstract
We report solution processable hole transport layer (HTL) for bulk heterojunction organic solar cells (BHJ OSCs) based on varied concentration of graphene oxide (GO) in aqueous suspension. The effects of varied concentration of GO at 1, 2, and 4 mg/mL on the morphological, optical, electrical, and photovoltaic properties of the OSCs have been studied. Device with the lowest concentration and least thickness of GO showed most optimized performance with a power conversion efficiency (PCE) of 2.73%, as compared to the higher concentrations, where the PCE reduced to 0.67 and 0.22% for the devices with HTL of 2 and 4 mg/mL, respectively. The remarkable reduction in the device performance at higher concentrations is mainly attributed to a drastic decrease in the short circuit current that reduced from 8.14 mA/cm(2) to 2.90 and 1.10 mA/cm(2) at 2 and 4 mg/mL, respectively. Similarly, the increased series resistance (R-s) from 6.89 Omega/cm(2) to 9.54 and 11.51 Omega/cm(2) has also reduced the device perforrriance. Optical transmittance has been decreased from more than 85% to less than 80% in the overall wavelength region at higher concentrations. Both the insulating properties of GO at higher thickness of HTL due to high concentration and inhomogeneous surface characteristics lead to a decrease in the device performance.