Effects of Alkali and Oxidation Treatments on Efficiency and Stability of CdS/CIGS Solar Cells

Curtis Walkons, University of Nevada, Las Vegas
Theresa M. Friedlmeier, Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg
Stefan Paetel, Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg
Wolfram Hempel, Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg
Marco Nardone, Bowling Green State University
Edward Barnard, Lawrence Berkeley National Laboratory
Kyoung E. Kweon, Lawrence Livermore National Laboratory
Vincenzo Lordi, Lawrence Livermore National Laboratory
Shubhra Bansal, University of Nevada, Las Vegas

Abstract

Three types of CIGS devices with varying treatments of RbF post-deposition treatment (PDT) and sodium are subjected to accelerated stress test (AST) conditions at elevated temperature (65 °C), voltage bias (short- vs open-circuit), and illumination (AM1.5 vs dark). RbF treatment with reduced CdS thickness shows an improvement in Voc and efficiency in this sample series, and also results in high FF and doping ~ 10 16 cm -3 . Cells with reduced sodium show a decrease in Voc and infrared QE results suggest a higher optical minimum bandgap. Heat and light soaking experiments at 50, 65, and 75 °C, open and short-circuit junction bias under AM1.5G illumination suggest stabilization of CIGS solar cells with addition of Na and RbF. SCAPS-1D simulations suggest reduction in thermally ionized defect density in ordered vacancy compound (OVC) and changes in conduction band offset with RbF post-deposition treatment. Further, simulations show an increase in shallow acceptor and donor density after open-circuit and short-circuit AST respectively. Preliminary light soaking results for oxidized CIGS with and without Na are also discussed.