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Effect of built-in electric field in photovoltaic InAs quantum dot embedded GaAs solar cell
KTH, School of Biotechnology (BIO), Theoretical Chemistry.
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2011 (English)In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 103, no 2, 335-341 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, three p-i-n GaAs solar cells were grown and characterized, one with InAs quantum dot (QD) layers embedded in the depletion region (sample A), one with QD layers embedded in the n (-) base region (B), and the third without QDs (control sample C). QD-embedded solar cells (samples A and B) show broad photoluminescence spectra due to QD multi-level emissions but have lower open-circuit voltages V (oc) and lower photovoltaic (PV) efficiencies than sample C. On the other hand, the short-circuit current density J (sc) in sample A is increased while it is decreased in sample B. Theoretical analysis shows that in sample B where the built-in electric field in QDs is zero, electrons tend to occupy QDs and strong potential variations exist around QDs which deteriorate the electron mobility in the n (-) base region so that J (sc) in sample B is decreased. Hole trapping and electron-hole recombination in QDs are also enhanced in sample B, resulting in a reduced V (oc) and thus a worse PV effect. In sample A, a strong built-in field exists in QD layers, which facilitates photo-carrier extraction from QDs and thus J (sc) is increased. However, QDs in the depletion region in sample A act also as recombination-generation centers so that the dark saturated current density is drastically increased, which reduces V (oc) and the total PV effect. In conclusion, a nonzero built-in electric field around QDs is vital for using QDs to increase the PV effect in conventional p-i-n GaAs solar cells.

Place, publisher, year, edition, pages
2011. Vol. 103, no 2, 335-341 p.
National Category
Materials Chemistry
URN: urn:nbn:se:kth:diva-33251DOI: 10.1007/s00339-010-6152-8ISI: 000289558900013ScopusID: 2-s2.0-79955852769OAI: diva2:414621
QC 20110504Available from: 2011-05-04 Created: 2011-05-02 Last updated: 2012-05-07Bibliographically approved
In thesis
1. Study of quantum dots on solar energy applications
Open this publication in new window or tab >>Study of quantum dots on solar energy applications
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis studies p-i-n GaAs solar cells with self-assembled InAs quantum dots (QDs) inserted. The values of this work lie in three aspects. First, by comparing the cell performance with QDs in the i-region and the n-region, the photocurrent (PC) production from QDs by thermal activation and/or intermediate band (IB) absorption is proved to be much lower in efficiency than tunneling. Second, the efficiency of PC production from QDs, characterized by PC spectrum, is helpful to design QD-based photodetectors. Third, closely spaced InAs QD layers allow a strong inter-layer tunneling, leading to an effective PC production from QD deep states, potential for solar cell application. Fourth, from the temperature-dependent PC spectra the minority photohole thermal escape is found to be dominant on PC production from QDs in the n-region. The thermal activation energy reflects the potential variations formed by electron filling in QDs.

Apart from InAs QDs, this thesis also explores the blinking correlation between two colloidal CdSe QDs. For QD distance of 1 µm or less, there is a bunched correlation at delay τ = 0, meaning that the two QDs blink synchronously. Such correlation disappears gradually as QD distance increases. The correlation is possibly caused by the stimulated emission between the two nearby QDs.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xii, 60 p.
Trita-BIO-Report, ISSN 1654-2312 ; 2012:12
Epitaxial InAs quantum dot solar cell
National Category
Nano Technology
urn:nbn:se:kth:diva-94021 (URN)978-91-7501-352-7 (ISBN)
Public defence
2012-06-04, FA32, AlbaNova Universitetscentrum, Stockholm, 14:00 (English)
QC 20120507Available from: 2012-05-07 Created: 2012-05-04 Last updated: 2012-05-07Bibliographically approved

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