Quantum confined CdS inclusion in graphene oxide for improved electrical conductivity and facile charge transfer in hetero-junction solar cell

Abstract

We employed a simple mechanism in tuning the electrical conductivity of graphene oxide (GO) by the inclusion of nano cadmium sulphide (CdS) and thereby, utilized it in a pn hetero-junction based solar cell. Two different kinds of hetero-junction solar cell devices are fabricated; one with CdS acting as a separate buffer layer in GO and in another, the GO was functionalized with quantum confined CdS particles. In both kinds, the n-type junction was interfaced with the p-type semiconductor Rose Bengal (RB). The nano CdS has the ability to harvest a useful spectral range of the solar spectrum and to retard the recombination rate between the junction interfaces and hence, promote the facile charge carrier transport within the device. The CdS functionalized GO exhibited a remarkable short circuit current density (J_sc) of 4 mA cm⁻², and an open circuit voltage (V_oc) of 685 mV, giving rise to an enhanced power conversion efficiency (η) of 1.97% in comparison to the planar GO hetero-junction. The enhancement in power conversion efficiency and the influence of nano CdS inclusion is analyzed and interpreted on the basis of the electrical studies performed with cyclic voltammetry (CV) and electrical impedance spectroscopy (EIS). From the electrical measurements, the charge storage capacitance of 138 F g⁻¹ and the minimal resistance of 440 Ω are incurred in GO/CdS nanocomposites. The obtained results are further supported by the various physico-chemical characterizations such as X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), absorption and luminescence emission studies and demonstrate their significance in photovoltaic applications.