India ERA-NET CZTS absorber material prepared by Modified Activated Reactive Sputtering technique for high efficiency thin films solar cells

Cu2ZnSnS4 (CZTS) is one of the popular materials in modern photovoltaic technology because of its abundance, non-toxicity, high absorption coefficient in the visible range of the solar spectra, and large charge carrier concentration that can be tuned in wide range. The project is about study of materials properties by ab initio software VASP using the Notur supercomputer facilities and solar cell performance by device modeling tool TCAD SILVACO. The following scientific tasks have been solved in the project such as estimation of the band gap of CZTS from electronic structure studies, influence of the secondary phases Cu2S, SnS, SnS2, ZnS on electrical and optical properties of CZTS by the effective medium theory, study of CZTS solar cell properties by device modeling by using the software TCAD SILVACO to clarify sensitivity of the solar cell parameters to variations of electrical parameters of CZTS. A computer program "Effective medium theory tool (EMAT)" has been designed that allows to study the influence of 0D, 1D, 2D nanomaterials on electrical and optical properties of hybrid and composite materials. Master and PhD students have been involved into the project. The project was the platform for exchange visits, knowledge exchange between collaborating teams. The results have been disseminated at International Conferences, lectures have been delivered to graduate and undergraduate students, and journal articles have been published.

The need for an efficient and cost effective photovoltaic (PV) power is well known and many laboratories are working on several concepts. Thin film PV has the potential and viability to break the cost barrier at the same time achieve high conversion effic iency. Among the several technological options, the p-n junctions of Copper Indium Gallium Sulphide/selenide (CIGS/Se) with CdS are the most preferred. CIGS is the absorber material which is most crucial for the efficiency of the solar cell. In order to a chieve further cost effectiveness, indium and gallium need to be replaced with zinc and tin respectively. Thus, CZTS became the focus as the most desirable absorber material for photovoltaics. It has both the technical advantages and cost factors. The sta ndard solar cell stack with CZTS is: Soda lime glass / Molybdenum (Mo) 500- 700 nm by Sputtering / p-CZTS (1- 2 micro meters) /n- CdS (chemical bath deposition: 500 ? 1000nm) /i-ZnO (50-90 nm by sputtering) /Al:ZnO (500-1000 nm by sputtering). The main fo cus is on the preparation of CZTS with desired phase, stoichiometry and smoothness of the surface. It may be cautioned that the window of growth parameters for achieving desired phase and stoichiometry is extremely narrow in almost all the techniques stud ied so far.