Implementation of graphene as hole transport electrode in flexible CIGS solar cells fabricated on Cu foil

CIGS solar cells have been fabricated on the chemical vapor deposited graphene film synthesized on flexible Cu foil. The CIGS solar cells fabricated with graphene/Cu foil hole transport electrode display highest achieving power conversion efficiency of ∼9.91% together with a fill factor of ∼64.75%. [Display omitted] •CIGS solar cells were fabricated on graphene film deposited on flexible Cu foil.•Graphene films employed as hole transport electrode in CIGS solar cells.•Graphene based device displayed superior PV characteristics over Mo/STS electrode.•High Voc and large FF are primarily responsible for superior device performance. Graphene has great potential to be used as electrode in many opto-electronic devices, owing to its superior optical and electrical properties. Graphene films have been employed as window electrode in various thin film solar cells. However, to date graphene film has not been used as hole transport electrode, particularly in CIGS solar cell. In this work, we have demonstrated a novel structure for graphene-based flexible CIGS solar cell, in which graphene film on flexible Cu foil was implemented as hole transport electrode. CIGS solar cells were directly fabricated on the chemical vapor deposited graphene film on Cu foil, without any transfer process. Several techniques, including Raman spectroscopy, X-ray diffraction, scanning electron microscopy, external quantum efficiency and J-V characteristics under illumination, have been used to investigate the device performance. The graphene-based device displayed power conversion efficiency of 9.91 ± 0.89% with a fill factor of 64.75 ± 7.34%, which are substantially higher compared to reference cell fabricated using conventional Mo/stainless steel electrode. High open circuit voltage together with substantially large fill factor is primarily responsible for high cell efficiency of graphene/Cu foil based device. This study provides a plausible implication of graphene as hole transport electrode in flexible CIGS photovoltaic devices.