• Hollars, Dennis R.
• Kanicki, Jerzy
• Zhang, Rui

Abstract

<jats:p>We report on a Cu(In,Ga)Se<jats:sub>2</jats:sub> (CIGS) solar cell fabricated on flexible stainless steel substrate by a low cost mass production roll-to-roll process. Fabricated device has a high energy conversion efficiency of 14%, with short circuit current density (<jats:italic>J</jats:italic><jats:sub>sc</jats:sub>) of 36.6 mA cm<jats:sup>-2</jats:sup> and open circuit voltage (<jats:italic>V</jats:italic><jats:sub>oc</jats:sub>) of 0.55 V. A two-dimensional (2D) simulation model for CIGS solar cell design and optimization was proposed. Opto-electrical properties showed that both experimental and simulated results are consistent with each other. The photons absorber in CIGS solar cells was prepared by co-sputtering metallic precursors of In and CuGa followed by thermal annealing in Se vapor. The device chemical properties were analyzed by secondary ion mass spectrometry (SIMS) and transmission/scan electron microscopy (TEM/SEM). Indium and gallium interdiffusions were observed during the growth of film, forming a band grading in CIGS layer. Accumulation of In at the top CIGS surface, resulting in a low bandgap, was responsible for the limited output open circuit voltage. Nano-scale voids were observed in the grown CIGS layer. A model based on Kirkendal effect and interdiffusion of atoms during selenization is developed to explain the formation mechanism of these voids. Na and K incorporation as well as metallic impurities diffusion are also discussed.</jats:p>

Topics

• density
• impedance spectroscopy
• surface
• stainless steel
• scanning electron microscopy
• simulation
• transmission electron microscopy
• two-dimensional
• forming
• annealing
• void
• current density
• spectrometry
• selective ion monitoring
• secondary ion mass spectrometry
• Gallium
• interdiffusion
• Indium