Properties of High Efficiency Nanostructured Copper Indium Gallium Selenide Thin Film Solar Cells

Abstract

Nowadays it is widely acknowledged that solar photovoltaic energy is one of the preferred options for sustainable management of the future energy needs of the world. For this, new technological processes, known as second and third generations, based on the use of thin films and nanomaterials, have recently been developed in order to reduce the cost of solar cells. Over the past few years, the yield of second-generation Cu(In, Ga)Se2 thin-film cells has exceeded 22 %. It was found that as nanostructured materials such as nanowire arrays often have a higher light absorption rate than thin films, they can therefore be used. This article aims to design and model nanostructured CIGS thin film solar cells based on indium tin oxide (ITO) nanowires. Modelling provides information on the operation of CIGS solar cells, as well as on the mechanisms of absorption and electric charge transport. The purpose of this work is to evaluate the electrical and optical characteristics (ISC, VOC, FF, η) of a ZnO/CdS/CIGS heterojunction thin film structure. Thus, an optimum efficiency of 17.57 % and a form factor of 76.56 % were achieved. Afterwards, the Mo film rear contact was replaced with ITO nanowires which were introduced into the CIGS-based solar cell. The results indicated that the solar cells under study exhibited very good photovoltaic performance, with an efficiency of 21.26 %. It is worth noting that this performance is higher than that of the corresponding CIGS thin film cells. In addition, the large active surface area of the ITO nanowire electrode and the short distance that the charge must travel helped to improve charge collection in the nanostructure. This would certainly increase the short circuit current ISC, and consequently the electrical efficiency. The simulation was based on the low-field mobility model, and on Shockley-Read-Hall (SRH) and Auger carrier transport and recombination models which may be activated in ATLAS-SILVACO (2D).