Improvement on conversion efficiency of CIGS thin film solar cell using electrochemical depleting

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)Se₂bulk. 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 CuInSe₂and 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%.