Photovoltaic and impedance spectroscopic characteristics of heterojunction of graphene-PEDOT:PSS composite and n-silicon prepared via solution-based process

Abstract

Recent investigations involving nanoscale energy conversion using two-dimensional nanomaterials such as graphene and transition metal dichalcogenides (TMDs) hold promise to mitigate future energy challenges. The heterojunction devices designed by interfacing 2D layers with 3D bulk semiconductors (2D/3D heterojunctions) including graphene/silicon and TMDs/silicon are widely explored for the photovoltaic characteristics. Developing a thorough understanding of the interfacial chemistry via impedance spectroscopic analysis will leverage the potential of these 2D/3D junctions for large-scale integrations. Here, the non-vacuum solution-processed reduced graphene oxide (rGO), poly(3,4-ethylenedioxythiophene):polystyrene sulphonate (PEDOT:PSS) and their composite (PEDOT:PSS(rGO)) were spin coated on the silicon (n-Si) substrates for fabrication of heterojunctions, with the device construct of rGO/n-Si, PEDOT:PSS/n-Si and PEDOT:PSS(rGO)/n-Si having Ohmic metal contacts in both top and bottom. The significant efficiency improvement of three orders for PEDOT:PSS(rGO)/n-Si device over the rGO/n-Si and PEDOT:PSS/n-Si heterojunction devices can be attributed to (i) increased conducting channels in the active region and (ii) reduced series resistance. Further, the impedance spectroscopy is employed to understand the interfacial chemistry of PEDOT:PSS(rGO)/n-Si solid-state junction, which is explained by a parallel resistance–capacitance circuit model.