Improvement on Conversion Efficiency of CIGS Thin Film Solar Cell Using Electrochemical Depleting

Abstract

In this work, electrochemical depleting, a reverse operation of electrochemical plating was adopted as an alternative of toxic KCN etching to conduct the surface modification process. The original CuInSe2 absorber layers were fabricated following a traditional electrodeposition-annealing approach. After the CuInSe2 and Cu(InGa)Se2 films were annealed, the films were then put into a sulfuric acid solution and electrochemical etched to form a Cu-deficient absorber layer on top of the CuInSe2 and Cu(InGa)Se2 bulk. The thickness of the Cu-deficient absorber layer can be controlled by depleting time. The X-ray diffraction and Raman spectroscopy indicated the formation of the Cu-deficient CIGS phase on the absorber surface. The current-voltage curves of CuInSe2 and Cu(InGa)Se2 cells with a thick Cu-deficient absorber layer on the surface displayed a kink effect which was probably caused by the increase in series resistance and light absorption in the Cu-deficient absorber layer instead of junction region. The cells with a thin Cu-deficient absorber layer yielded higher efficiency of Cu(InGa)Se2 cells. Through electrochemical depleting on the surface of absorber layer of the Cu(InGa)Se2, the fill factor and the efficiency of the Cu(InGa)Se2 solar cell is improved respectively from 58% to 65% and from 11.4% to 13.8%.