Crystal Quality Improvement of CuInS₂ Thin Film by Two Step Fabrication Method with Bismuth Addition

Abstract:

CuInS₂ (CIS) is the promising candidate of an absorber layer of high efficiency thin film solar cells. The crystal quality of CIS is one of the important factors for high efficiency. A chemical doping approach using antimony and bismuth (Bi) is well known for improving crystal quality in Cu (In,Ga)Se₂ thin films. In this study, the effect of Bi doping on evaporated CIS thin films was investigated. A CIS thin film without Bi doping annealed at 600°C showed small crystal grain size of ~1 μm, which was smaller than the CIS film thickness of 2 μm. The small addition of 50 nm-thick Bi promoted crystal growth and large grain size of greater than 1 μm, which was comparable to the CIS film thickness, was realized. The CIS films without and with Bi addition had surface precipitates identified as Cu-S and Cu-Bi-S compounds, respectively. The crystal growth promotion by Bi addition can be attributed to that the Cu-Bi-S compound which has lower melting point of 470~490°C than that of the Cu-S compound of 507°C acted as flux for crystal growth.

• Periodical: Applied Mechanics and Materials (Volume 372)
• Pages: 563-566
• DOI: https://doi.org/10.4028/www.scientific.net/AMM.372.563
• Online since: August 2013
• Authors: Shohei Fukamizu, Daisuke Hironiwa, Takashi Minemoto
• Keywords: Chalcopyrite, Compound Semiconductor, CuInS₂, Solar Cell, Thin Film

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