Recent R&D progress in solar frontier's small-sized Cu(InGa)(SeS)2 solar cells

Our resent achievement of the record breaking 20.9% efficiency (independently confirmed by Fraunhofer ISE) with small-sized CIS-based solar cell will be discussed in this paper by means of comparison with our previous result of 19.7%. The new record was mainly achieved by an improved J
_sc
arising from modified depth profile of the absorber layer and the doping concentration of the transparent conductive oxide (TCO) layer. Combination of these two modifications drastically enhances light absorption at a longer wavelength region, leading to J
_sc
improvement of about 3 mA/cm
²
without losing V
_oc
nor FF. This new 20.9% efficiency record resulted from a CIGS cell cut from a 30 cm by 30 cm substrate produced using the same method and materials we use in our factories, sputtering-selenization formation method with Cd-free buffer layer.