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Title: Formation of Different Phases of CuxTe and Their Effects on CdTe/CdS Solar Cells

Abstract

Material studies and device applications of CuxTe in an NREL-developed CdTe solar cell structured as glass/Cd2SnO4/ZnSnOx/CdS/CdTe are presented. The CuxTe primary back contact was formed by evaporating a Cu layer with various thicknesses at room temperature on HNO3/H3PO4 (NP) solution etched CdTe layer. A post-annealing was then followed. The structural evolution and electrical properties of CuxTe were investigated. Cu/Te ratio and post-annealing temperature are two processing parameters in this study. The CuxTe phases are mainly controlled by the Cu/Te ratio. After a post-annealing at a low temperature, such as 100 C, no CuxTe phase transformation from its as-deposited phase was observed. A post-annealing treatment at a higher temperature, such as 250 C, can reveal the stoichiometric CuxTe phases based on the Cu/Te ratio used in the devices. But a post-annealing at a further higher temperature, such as 400 C, resulted in a complicated CuxTe phase appearance. CuTe, Cu1.4Te, and Cu2Te are three major phases detected by X-ray diffraction (XRD) for different Cu thickness application annealed at 250 C. Application of Cu thicker than 60 nm degrades open-circuit voltage (Voc) and shunting resistance (Rsh), but increases series resistance (Rs). The correlation between device performance and the CuxTe back contact illustrates thatmore » the process used for forming the Cu2Te back contact failed to produce good fill factor (FF) and also introduced higher barrier height. The best device was observed for a back contact with a mixed Cu1.4Te and CuTe phases.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
915280
DOE Contract Number:
AC36-99-GO10337
Resource Type:
Journal Article
Resource Relation:
Journal Name: Thin Solid Films; Journal Volume: 515; Journal Issue: 18, 2007
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; SOLAR CELLS; CADMIUM TELLURIDE SOLAR CELLS; CADMIUM SULFIDE SOLAR CELLS; Solar Energy - Photovoltaics

Citation Formats

Zhou, J., Wu, X., Duda, A., Teeter, G., and Demtsu, S. H. Formation of Different Phases of CuxTe and Their Effects on CdTe/CdS Solar Cells. United States: N. p., 2007. Web. doi:10.1016/j.tsf.2007.03.032.
Zhou, J., Wu, X., Duda, A., Teeter, G., & Demtsu, S. H. Formation of Different Phases of CuxTe and Their Effects on CdTe/CdS Solar Cells. United States. doi:10.1016/j.tsf.2007.03.032.
Zhou, J., Wu, X., Duda, A., Teeter, G., and Demtsu, S. H. Mon . "Formation of Different Phases of CuxTe and Their Effects on CdTe/CdS Solar Cells". United States. doi:10.1016/j.tsf.2007.03.032.
@article{osti_915280,
title = {Formation of Different Phases of CuxTe and Their Effects on CdTe/CdS Solar Cells},
author = {Zhou, J. and Wu, X. and Duda, A. and Teeter, G. and Demtsu, S. H.},
abstractNote = {Material studies and device applications of CuxTe in an NREL-developed CdTe solar cell structured as glass/Cd2SnO4/ZnSnOx/CdS/CdTe are presented. The CuxTe primary back contact was formed by evaporating a Cu layer with various thicknesses at room temperature on HNO3/H3PO4 (NP) solution etched CdTe layer. A post-annealing was then followed. The structural evolution and electrical properties of CuxTe were investigated. Cu/Te ratio and post-annealing temperature are two processing parameters in this study. The CuxTe phases are mainly controlled by the Cu/Te ratio. After a post-annealing at a low temperature, such as 100 C, no CuxTe phase transformation from its as-deposited phase was observed. A post-annealing treatment at a higher temperature, such as 250 C, can reveal the stoichiometric CuxTe phases based on the Cu/Te ratio used in the devices. But a post-annealing at a further higher temperature, such as 400 C, resulted in a complicated CuxTe phase appearance. CuTe, Cu1.4Te, and Cu2Te are three major phases detected by X-ray diffraction (XRD) for different Cu thickness application annealed at 250 C. Application of Cu thicker than 60 nm degrades open-circuit voltage (Voc) and shunting resistance (Rsh), but increases series resistance (Rs). The correlation between device performance and the CuxTe back contact illustrates that the process used for forming the Cu2Te back contact failed to produce good fill factor (FF) and also introduced higher barrier height. The best device was observed for a back contact with a mixed Cu1.4Te and CuTe phases.},
doi = {10.1016/j.tsf.2007.03.032},
journal = {Thin Solid Films},
number = 18, 2007,
volume = 515,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • All polycrystalline CdS/CdTe heterojunction solar cells with various thicknesses of CdS film were prepared by the coating and sintering method in an attempt to optimize the thickness of the sintered CdS film whose role is to be the window as well as the front contact for the CdS/CdTe solar cell. The thickness of the CdS films was varied from 14 to 55 ..mu..m by changing the screen mesh size of a screen printer and the solid-liquid ratio of the slurry which consisted of CdS powder, 9 weight percent CdCl/sub 2/ and propylene glycol. Average grain size of the sintered CdSmore » films increases and porosity decreases with an increase in film thickness. Electrical resistivity of the sintered CdS films shows a minimum value in 35 ..mu..m thick film. Highest optical transmission is observed in 20 ..mu..m thick CdS film. The CdCl/sub 2/ remaining in the CdS film after the sintering causes an increase in the thickness of the CdS/sub 1-x/Te/sub x/ solid solution layer, acting as a sintering aid, at the interface between the CdS and the CdTe films. The combination of the optical transmission, the solid solution layer, and the sheet resistance effects resulted in the highest solar efficiency in a CdS/CdTe heterojunction solar cell with 20 ..mu..m thick CdS layer.« less
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