Cu(In_0.7Ga_0.3)Se₂ Thin Film Solar Cell Prepared By Dry Method

After almost 30 years development, copper indium gallium selenium Cu(In0.7,Ga0.3)Se2, is one of the relatively cheap solar cell materials. Its large conversion efficiency (21.5%) and stable operating behavior have raised extensive interests in international photovoltaic industry. However, the industrialization of this solar cell is still not realized. The main difficulties are as follows:first, relatively mature preparation methods of CIGS thin films use wet and dry complicated procedures and cannot gurantee the uniformity of samples with larger areas. Second, critical equipments and controlling procedures are required to achieve large scale production of cells with larger areas (300mm×300mm) rather than those small samples prepaired in laboratories. In addition, Cd pollution is now a problem of mainstream technology. In this work, CIGS thin film solar cells are mainly preparated by sputtering. In principle, epidemics associated with wet processing, relatively complex procedure, polution and interface defects can be elimited.In this paper, CIGS thin film solar cells were prepared on glass substrates by magnetron sputtering. The effects of deposition parameters on the structural, electrical, and optical properties of all the layers consisting of CIGS thin film solar cells were investigated systematically by scanning electron microscopy (SEM), x-ray diffractometry (XRD), four point probe and PV Testing System, respectively. The results indicate that:(1) In preparation of Mo film of CIGS back electrodes by DC magnetron sputtering, good surface morphology and high conductivity have been achieved by adapting a low Ar pressure of 0.2Pa and a high depositing power of 148W.(2) The best sputtering condition for ZnS buffer layer of CIGS cell preparated by RF sputtering method is Ar pressure 0.4Pa and sputtering power of 200W.(3) The transparent conductive ZAO for the CIGS cell was preparated by RF-Sputtering (ZnO)0.98 (Al2O3)0.02 target. Growth of C-axis prefered crystal structure with good photoelectric properties has been achieved by using an Ar pressure of 0.2Pa and a sputtering power of 255W followed by annealing at 350oC.(4) Battery back electrode, absorbing layer, the window layer consisting of a buffer layer and a transparent electrode of CIGS were preparated layer by layer by using magnetron sputtering technology. Preliminary study on the I-V characteristics and spectral response of the device has been also carried out.