Exploring graphene's potential as a transparent conductive layer in Cu2ZnSnS4 superstrate solar cells

Abstract

The fabrication of environmentally friendly, semi-transparent, high-performance and cost-effective inorganic solar cells has been the subject of recent extensive study. One area of study involves incorporating one-dimensional nanostructures and high quality transparent conductive layers into the conventional thin film solar cell systems. The objective of this particular investigation was, therefore, to construct such a structure by integrating Graphene-ZnO-Nanorods (NRs) hybrid structure into a conventional Cu2ZnSnS4 (CZTS) thin film solar cell architecture. The process involved synthesizing vertically-aligned ZnO NRs, coated with thin layers of SnO2 and CdS, on chemical vapor deposited graphene pre-coated glass substrates. Following the SnO2-passivation and CdS coating, vertically well-aligned ZnO NRs were then decorated with a 500 nm-thick layer of CZTS using a one-step thermal evaporation technique.This process led to the manufacture of a superstrate solar cell with SLG /Graphene/ZnO-NRs/CdS/CZTS/Ag device structure as an example of graphene’s application in optoelectronic devices. To reveal the physical properties of the grown graphene and deposited CZTS thin films, they were subjected to various characterization techniques. The structural, chemical and optical analyses results showed the formation of a single-phase kesterite CZTS thin film with a copper-deficient composition and an optical band gap of 1.47 eV on glass substrate and single layer growth of graphene on Cu-foil substrate, which was subsequently successfully transferred onto glass substrates. Electrical measurements unveiled the existence of two different VCu point defects in CZTS with thermal activation energies of 45 meV and 180 meV. The manufactured superstrate solar cell exhibited a short-circuit current density of 9.34 mA/cm2, an open-circuit voltage of 390.6 mV, a fill factor of 17.2%, and an energy conversion efficiency of 0.63%.