The effects of CdCl sub 2 on the electronic properties of molecular-beam epitaxially grown CdTe/CdS heterojunction solar cells

Journal Article · Mon Jul 15 00:00:00 EDT 1991 · Journal of Applied Physics; (USA)

DOI:https://doi.org/10.1063/1.349652· OSTI ID:5668820

Ringel, S A; Smith, A W; MacDougal, M H; Rohatgi, A ^[1]

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1. School of Electrical Engineering and Microelectronics Research Center, Georgia Institute of Technology, Atlanta, Georgia 30332 (US)

Significant improvements in CdTe/CdS solar cell efficiency are commonly observed as a result of a postdeposition CdCl{sub 2} dip followed by a 400 {degree}C heat treatment during cell processing which increases CdTe grain size. In this paper, we investigate the electronic mechanisms responsible for CdCl{sub 2}-induced improvement in cell performance along with possible performance-limiting defects resulting from this process in molecular-beam epitaxy-grown polycrystalline CdTe/CdS solar cells. Current density-voltage-temperature ({ital J}-{ital V}-{ital T}) analysis revealed that the CdCl{sub 2} treatment changes the dominant current transport mechanism from interface recombination/tunneling to depletion region recombination, suggesting a decrease in the density and dominance of interface states due to the CdCl{sub 2} treatment. It is shown that the change in transport mechanism is associated with (a) an increase in heterojunction barrier height from 0.56 to 0.85 eV, (b) a decrease in dark leakage current from 4.7{times}10{sup {minus}7} A/cm{sup 2} to 2.6{times}10{sup {minus}9} A/cm{sup 2} and, (c) an increase in cell {ital V}{sub oc} from 385 to 720 mV. The CdCl{sub 2} also improved the optical response of the cell. Substantial increases in the surface photovoltage and quantum efficiency accompanied by a decrease in the bias dependence of the spectral response in the CdCl{sub 2}-treated structures indicate that the CdCl{sub 2} treatment improves carrier collection from the bulk as well as across the heterointerface. However, deep level transient spectroscopy measurements detected a hole trap within the CdTe depletion region of the CdCl{sub 2}-treated devices at {ital E}{sub {ital v}} + 0.64 eV which is attributed to the formation of {ital V}{sub Cd}-related defects during the annealing process after the CdCl{sub 2} dip.

• OSTI ID: 5668820
• Journal Information: Journal of Applied Physics; (USA), Vol. 70:2; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
CADMIUM SULFIDE SOLAR CELLS
EFFICIENCY
FABRICATION
CADMIUM TELLURIDE SOLAR CELLS
CADMIUM CHLORIDES
CADMIUM SULFIDES
CADMIUM TELLURIDES
HETEROJUNCTIONS
MOLECULAR BEAM EPITAXY
PERFORMANCE
CADMIUM COMPOUNDS
CADMIUM HALIDES
CHALCOGENIDES
CHLORIDES
CHLORINE COMPOUNDS
DIRECT ENERGY CONVERTERS
EPITAXY
EQUIPMENT
HALIDES
HALOGEN COMPOUNDS
INORGANIC PHOSPHORS
JUNCTIONS
PHOSPHORS
PHOTOELECTRIC CELLS
PHOTOVOLTAIC CELLS
SEMICONDUCTOR JUNCTIONS
SOLAR CELLS
SOLAR EQUIPMENT
SULFIDES
SULFUR COMPOUNDS
TELLURIDES
TELLURIUM COMPOUNDS
140501* - Solar Energy Conversion- Photovoltaic Conversion