Optical simulation of solar cell based on ZnO/ZTO core–shell nanowire array embedded in CZTS layer

Abstract

We present an optical simulation of a solar cell with superstrate configuration employing core (Zinc Oxide (ZnO))/shell (Zinc Tin Oxide (ZTO)) vertically-aligned nanowire array embedded in Kesterite Cu2ZnSnS4 (CZTS) layer and coated by an Al2O3 anti-reflection coating. The chosen composition of Sn (0.23) in ZTO shell is such as the conduction band offset at the CZTS-ZTO heterointerface is “spike-like” which is favorable for CZTS solar performance. The simulation is made using a rigorous coupled wave analysis (RCWA). We found that the reflectance of the investigated solar cell is much smaller than that of planar solar cell involving the same materials which led to an important increase of the absorption. The Aluminum Oxide (Al2O3) anti-reflection coating layer leads to an enhancement of ideal short circuit current density by 29%. The optimal value of the current (27 mA/cm2), obtained for anti-reflection coating layer thickness of 0.07 µm, nanowires height of 1 µm, nanowires diameter below 0.2 µm and ratio of period and diameter above 4, is greater by about 15.5% than the one of planar solar cell involving the same amount of materials. This improvement added to the radial geometry advantages of the investigated solar cell, makes this device a good candidate for the nanostructured solar cells.