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Electrochemical etching of molybdenum for shunt removal in thin film solar cells

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Author: Hovestad, A. · Bressers, P.M.M.C. · Meertens, R.M. · Frijters, C.H. · Voorthuijzen, W.P.
Type:article
Date:2015
Publisher: Springer
Place: Dordrecht
Source:Journal of Applied Electrochemistry, 45, 745–753
Identifier: 526257
doi: doi:10.1007/s10800-015-0829-9
Keywords: Materials Energy · Alkaline etching · CIGS · Molybdenum · Oxidation · Thin film solar cells · Industrial Innovation · Nano Technology · TFT - Thin Film Technology · TS - Technical Sciences

Abstract

High yield and reproducible production is a major challenge in up-scaling thin film Cu(In,Ga)Se2(CIGS) solar cells to large area roll-to-roll industrial manufacturing. Pinholes enabling Ohmic contact between the ZnO:Al front-contact and Mo back contact of the CIGS cell create electrical shunts that are detrimental to the output of the cell and production yield. This paper describes a selflimiting electrochemical etching method to reduce shunts by dissolving Mo exposed through pinholes in a CIGS cell. Anodic polarisation measurements show that Mo oxidizes at a high rate in alkaline solutions. At pH 14 the current density was sufficient to allow fast Mo oxidation. However, at this pH the Mo film is initially converted to a MoO2 film that retards further oxidative dissolution. Addition of K3Fe(CN)6 as oxidising agent accelerates the MoO2 film dissolution resulting in complete Mo film removal in a few minutes. Standard and shunted CIGS cells treated with the Mo etching solution showed a reduction in the number of low shunt resistant areas. In shunted CIGS cells an increase in cell conversion efficiency from 3 to 5.9 % was also found.