Optimization of Ti/TiN/Mo back contact properties for Cu(In,Ga)Se2 solar cells on polyimide foils

• Published in: Thin solid films Vol. 519; no. 21; pp. 7453 - 7457
• Main Authors: BLÖSCH, P, GÜTTLER, D, CHIRILA, A, TIWARI, A. N
• Format: Conference Proceeding Journal Article
• Language: English
• Published: Amsterdam Elsevier 31.08.2011
• Subjects: Applied sciences; Bias; CIGS; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Contact; CONTACTS; COPPER INDIUM SELENIDE; COPPER SELENIDE; Cross-disciplinary physics: materials science; rheology; CURRENT DENSITY; Deposition by sputtering; Electric contacts; ELECTRICAL CONDUCTIVITY; Electrical properties of specific thin films; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Energy; Exact sciences and technology; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Natural energy; Photovoltaic cells; Photovoltaic conversion; Physics; POLYIMIDES; SOLAR CELLS; Solar cells. Photoelectrochemical cells; Solar energy; Solar power generation; SPUTTERING; Structure and morphology; thickness; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology; Titanium nitride; Polyimide; Flexible substrate; Gallium; Electrical conductivity; Indium selenides; Voltage current curve; Electrical back contact; CIGS; Optimization; Sputtering; Thin film; Physical vapor deposition; Titanium; Stress effects; Copper; Current density; DC sputtering; Quantitative analysis; Scanning electron microscopy; Voltage measurement; Multilayer; Ti/TiN/Mo; Multiple layer; Titanium nitride; Electric contact; Quantum yield; X ray diffraction; Molybdenum; Solar cell; Copper selenides; Film stress; Reactive sputtering; Sputter deposition; Microstructure; Curvature; Gallium selenides; Bilayers
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2010.12.187

Molybdenum is conventionally used as electrical back contact for Cu(In,Ga)Se2 (CIGS) solar cells. In this work, a multifunctional stack of Ti/TiN/Mo is introduced as back contact for flexible CIGS solar cells. The multilayer back contact was deposited on 25 mu m thick polyimide foil by means of DC reactive sputtering. To optimize electrical conductivity and film stress of the alternative back contact sputter parameters such as total gas pressure, sputtering power, substrate temperature and RF substrate bias have been varied. XRD measurements and quantitative analysis of foil curvature revealed that the film stress is significantly influenced by the argon gas pressure and sputtering power. The electrical conductivity was improved by applying higher sputtering power or RF substrate bias. Analysis of the film microstructure with SEM shows that applied substrate bias influences the density of the sputtered film. The solar cells processed on Ti/TiN/Mo as well as on a conventional Mo bilayer back contact have been compared using standard current density to voltage (J-V) measurements and external quantum efficiency measurements. Conversion efficiencies of 13.4% for the alternative and 14.9% for the conventional design have been obtained.