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

Abstract

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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> improvement of about 3 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> without losing V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> 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.