Cu(In, Ga)Se2 solar cells on low cost mild steel substrates. (15th November 2018)

• Record Type: Journal Article
• Authors: Zortea, Lucas; Nishiwaki, Shiro; Weiss, Thomas Paul; Haass, Stefan; Perrenoud, Julian; Greuter, Lukas; Feurer, Thomas; Palaniswamy, Ganesan; Buecheler, Stephan; Tiwari, Ayodhya N.
• Is Part Of: Solar energy. Volume 175(2018)
• Page Start: 25
• Page End: 30
• Publication Date: 2018-11-15
• Subjects: CIGS thin films -- Flexible solar cells -- Steel -- Diffusion barrier -- Roll-to-roll; Solar energy -- Periodicals; Solar engines -- Periodicals; 621.47
• DOI: 10.1016/j.solener.2017.12.057
• Languages: English
• ISSNs: 0038-092X

Abstract

Highlights: 18.0% certified conversion efficiency for CIGS on mild steel substrate. The used industrially scalable Ni/Cr diffusion layer sufficiently suppresses detrimental element diffusion. The Ni/Cr diffusion barrier is effective up to 500 °C nominal substrate temperature. For higher substrate temperatures impurity induced deep defects cause additional recombination losses. Abstract: Thin film Cu(In, Ga)Se2 (CIGS) solar modules can be grown on flexible and lightweight substrates allowing their direct integration into building elements. Such multifunctional building elements would significantly reduce the installation cost of photovoltaic systems provided that CIGS solar cells with high conversion efficiency can be obtained. Also, there is a need for low cost substrate foil. Mild steel is a promising low cost substrate material due to its excellent mechanical stability and already wide acceptance as component in building envelopes and in numerous other applications. During the growth of the CIGS absorber layer certain elements, e.g. iron, can diffuse from the metallic substrate into the semiconductor deteriorating the device performance. Here we present an effective diffusion barrier and device architecture for processing of highly efficient CIGS solar cells on mild steel substrates. The CIGS absorber layers were grown on mild steel foils by a multistage co-evaporation process at different substrate temperatures. The mild steel substrates were plated with an industrially scalable electrodeposited Ni/Cr bi-layer. The diffusion barrier layer properties of this Ni/Cr coating were investigated directly by measuring the metallic impurities within the absorber by secondary ion mass spectrometry and indirectly by admittance spectroscopy. The Ni/Cr bi-layer was found to be effective up to a nominal CIGS growth temperature of 500 °C. A certified cell efficiency of 18.0% was achieved on a Ni/Cr coated mild steel substrate using a low temperature CIGS deposition process and a NaF and RbF post deposition treatment method.