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Hidden energy levels? Carrier transport ability into CdS/CdS1-xSex quantum dot solar cells affected by Cd-Cd levels formation

Abstract

In quantum dot sensitized solar cells (QDSSC), a cascade energy level structure controlled by assembly of cadmium-chalcogenide quantum dots can remarkably improve the sunlight harvesting and charge carrier lifetime. Despite the advantages for using co-sensitizers, energy conversion efficiencies are still low. Increased understanding of the causes about the low photoconversion efficiency (PCE) will contribute to provide a straightforward approach to improve solar cell performance by exploiting co-sensitization. Herein we discuss how the excess of cadmium causes structural disorder and defect levels impacting the PCE of QDSSC devices. Thus, outer CdS1-xSex/inner CdS QD-co-sensitized B,N,F-co-doped-TiO2 nanotubes (BNF-TNT) were prepared. Chalcogenides were deposited by SILAR method on BNF-TNT, varying the load of CdS as inner sensitizer, while for CdS1-xSex, five SILAR cycles were used (5-CdS1-xSex), controlling the nominal S/Se molar ratio into ternary alloy. Cd defects denominated as Cd-Cd energy levels were observed during CdS sensitization. Although incorporation of outer CdS1-xSex provides a tunable band gap to achieve a good band alignment for carrier separation, Cd-Cd energy levels into the sensitizers act as recombination centers, limiting the overall electron flow into the BNF-TNT/CdS/CdS1-xSex interface. A maximum PCE of 2.58 % was reached under standard AM 1.5G solar illumination at 100 mW cm−2. Additional limitations from SILAR as a strategy deposition of QD are also addressed to influence the PCE of QDSSC.

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Publication details

The article was received on 31 Aug 2018, accepted on 23 Nov 2018 and first published on 06 Dec 2018


Article type: Paper
DOI: 10.1039/C8NR07073C
Citation: Nanoscale, 2018, Accepted Manuscript
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    Hidden energy levels? Carrier transport ability into CdS/CdS1-xSex quantum dot solar cells affected by Cd-Cd levels formation

    A. F. Gualdron-Reyes, A. M. Meléndez, J. F. Tirado, M. A. Mejia-Escobar, F. Jaramillo and M. E. Niño-Gómez, Nanoscale, 2018, Accepted Manuscript , DOI: 10.1039/C8NR07073C

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