Developing CdTe homojunctions applying high throughput deposition

Technical Report · Mon Oct 24 04:00:00 EDT 2022

DOI:https://doi.org/10.2172/1894358· OSTI ID:1894358

McCloy, John S. ^[1]; Duenow, Joel ^[2]; Murgesan, Magesh ^[3]; Gul, Rubi ^[3]; Swain, Santosh ^[3]

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1. Washington State Univ., Pullman, WA (United States); Washington State University
2. National Renewable Energy Lab. (NREL), Golden, CO (United States)
3. Washington State Univ., Pullman, WA (United States)

In this project, we attempted to make CdTe homojunctions using single crystal p-type doped substrates and closed-space sublimation epitaxy (CSSE) n-type doped films. The project included modeling which determined the ideal thickness for the n-type layer as being <200 nm. Boules of high concentration indium-doped CdTe and CdSe_0.4Te_0.6 (CST) were grown using modified vertical Bridgman (MVB) methods. Similarly, iodine-doped CdTe crystals were grown for the first time. Washington State University (WSU) stock phosphorus-doped CdTe was used as the p-type substrate layer. The crystals were characterized by Hall effect and time-resolved photoluminescence (TRPL, for electrical properties), photoluminescence microscopy (for uniformity), X-ray diffraction (for crystal structure), and glow discharge mass spectrometry (GDMS, for dopant and impurity concentration). CdTe:I crystals were also characterized by visible and infrared transmission measurements, and various Cd or Te heat treatments were performed to assess changes in optical and electrical properties. The grown n-type materials – CdTe:In, CdSe0.4Te0.6:In, and CdTe:I – were provided to the National Renewable Energy Laboratory (NREL) for growth of CSSE thick films for characterization by two photon TRPL (for carrier lifetime), electron back-scatter diffraction (EBSD, to assess epitaxy), and Hall effect. Several measurements of secondary ion mass spectroscopy (SIMS) were performed. Nearly 100% of the indium from the crystal was incorporated into the measured thick films, while only ~2-22% of the iodine from the crystal was incorporated. The net result of the diffusion issue is that homojunction devices created using CSSE have a buried homojunction, as indicated by the near infrared peak in the external quantum efficiency (EQE). Various parameterization of front and back contacts suggested that the poor device performance was primarily a result of this buried junction and not due to other effects. There may also be an issue with the CSSE film lifetime in addition to the dopant profile.

• Research Organization: Washington State Univ., Pullman, WA (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office
• DOE Contract Number: EE0009365
• OSTI ID: 1894358
• Report Number(s): WSU--SIPS-HJ-FIN
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
CdSeTe
CdTe
Crystal Growth
Homojunction
Solar Cell
n-Type Doping