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Research Papers

Experimental Analysis of the Operation of Quantum Dot Intermediate Band Solar Cells

[+] Author and Article Information
N. López

Instituto de Energía Solar–UPM, ETSIT de Madrid, Ciudad Universitaria sn, 28040 Madrid, Spainnlomar@ies-def.upm.es

A. Martí, A. Luque

Instituto de Energía Solar–UPM, ETSIT de Madrid, Ciudad Universitaria sn, 28040 Madrid, Spain

C. Stanley, C. Farmer, P. Diaz

Department of Electronics and Electrical Engineering, University of Glasgow, Glasgow G12 8QQ, UK

J. Sol. Energy Eng 129(3), 319-322 (Oct 04, 2006) (4 pages) doi:10.1115/1.2735344 History: Received December 14, 2005; Revised October 04, 2006

With a 63.2% theoretical efficiency limit, the intermediate band solar cell (IBSC) is a new photovoltaic device proposed to overcome the 40.7% efficiency limit of conventional single gap solar cells. Quantum dot technology can be used to take the IBSC concept into practice. In this respect, the results of experiments carried out recently to characterize IBSC solar cells containing different numbers of InAs quantum dot layers as well as the theoretical models used to describe and analyze the related experimental data are summarized here. Electroluminescence and quantum efficiency measurements confirm that the main operating conditions for IBSCs are complied with in structures with a low number of QD layers. These conditions include the production of photocurrent from absorption of below band gap energy photons and the formation of distinctive quasi-Fermi levels associated with each electronic band (i.e., the conduction, valence, and intermediate bands).

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References

Figures

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Figure 1

Energy band diagram in an intermediate band semiconductor. The generation rate of electrons is represented by ge when the transitions are from the IB to the CB; gh is the generation rate of holes in the VB as a consequence of electron transitions from the VB to the IB and geh is the generation rate of electron–hole pairs between the VB and the CB. re, rh, and reh are the inverse processes or recombination rates. EL and EH denote the two subband gaps into which the IB divides the original gap EG.

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Figure 2

Internal structure of a QD-IBSC

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Figure 3

Photograph of a small area device

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Figure 4

Current density versus voltage characteristics under 1 sun illumination (100mWcm−2): (1) GaAs reference cell, (A1677); (2) sample with 10×QDs and δ doping (A1681); (3) sample with 10×QDs and no δ doping (A1684); (4) sample with 20×QDs and δ doping (A1938); (5) sample with 50×QDs and δ doping (A1777). The illuminated areas listed in Table 1 have been used to calculate the current densities.

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Figure 5

Current density versus voltage characteristics under dark conditions: (1) GaAs reference cell, (A1677); (2) sample with 10×QDs and δ doping (A1681); (3) sample with 10×QDs and no δ doping (A1684); (4) sample with 20×QDs and δ doping (A1938); (5) sample with 50×QDs and δ doping (A1777). The “device area” listed in Table 1 has been used to calculate the current density.

Grahic Jump Location
Figure 6

Normalized quantum efficiency: (1) GaAs reference cell, (A1677); (2) sample with 10×QDs and δ doping (A1681); (3) sample with 10×QDs and no δ doping (A1684); (4) sample with 20×QDs and δ doping (A1938)

Grahic Jump Location
Figure 7

Normalized electroluminescence spectra: (1) GaAs reference cell, (A1677 in Table 1); (2) sample with 10×QDs and δ doping (A1681); (3) sample with 10×QDs and no δ doping (A1684); (4) sample with 20×QDs and δ doping (A1938). Samples are biased with a current density of 5Acm−2.

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