Polycrystalline Cu(InGa)Se2 Thin-Film Solar Cells with ZnSe Buffer Layers

A ZnSe buffer layer has been applied as an attractive alternative to a CdS buffer layer in the development of polycrystalline Cu(InGa)Se2 (CIGS) thin-film solar cells, thus eliminating entirely the use of cadmium by employing the ZnO/ZnSe/CIGS structure. Moreover, we propose the use of a new deposition method for ZnSe buffer layers, the atomic-layer deposition (ALD) method. This method is basically the same as an “atomic-layer epitaxy” method but is applied to polycrystalline materials. Currently the best efficiency of CIGS thin-film solar cells with an about 10-nm-thick ZnSe buffer layer is 11.6%. Applying irradiation with a solar simulator under one-sun (AM-1.5, 100 mW/cm2) conditions, the efficiency of these cells was improved from about 5% to over 11% due to increased open-circuit voltage and fill factor with no change in short-circuit current density even after six-hour irradiation.