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Facile solution growth of vertically aligned ZnO nanorods sensitized with aqueous CdS and CdSe quantum dots for photovoltaic applications.

Luan C, Vaneski A, Susha AS, Xu X, Wang HE, Chen X, Xu J, Zhang W, Lee CS, Rogach AL, Zapien JA - Nanoscale Res Lett (2011)

Bottom Line: Vertically aligned single crystalline ZnO nanorod arrays, approximately 3 μm in length and 50-450 nm in diameter are grown by a simple solution approach on a Zn foil substrate.A thin Al2O3 layer deposited prior to quantum dot anchoring successfully acts as a barrier inhibiting electron recombination at the Zn/ZnO/electrolyte interface, resulting in power conversion efficiency of approximately 1% with an improved fill factor of 0.55.The in situ growth of ZnO nanorod arrays in a solution containing CdSe quantum dots provides better contact between two materials resulting in enhanced open circuit voltage.

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Affiliation: Department of Physics and Materials Science, City University of Hong Kong, Kowloon, Hong Kong SAR. andrey.rogach@cityu.edu.hk.

ABSTRACT
Vertically aligned single crystalline ZnO nanorod arrays, approximately 3 μm in length and 50-450 nm in diameter are grown by a simple solution approach on a Zn foil substrate. CdS and CdSe colloidal quantum dots are assembled onto ZnO nanorods array using water-soluble nanocrystals capped as-synthesized with a short-chain bifuncional linker thioglycolic acid. The solar cells co-sensitized with both CdS and CdSe quantum dots demonstrate superior efficiency compared with the cells using only one type of quantum dots. A thin Al2O3 layer deposited prior to quantum dot anchoring successfully acts as a barrier inhibiting electron recombination at the Zn/ZnO/electrolyte interface, resulting in power conversion efficiency of approximately 1% with an improved fill factor of 0.55. The in situ growth of ZnO nanorod arrays in a solution containing CdSe quantum dots provides better contact between two materials resulting in enhanced open circuit voltage.

No MeSH data available.


J-V characteristics of different QDSC. ZnO nanorods (curve 1: filled circle), ZnO nanorods decorated with CdS QDs (curve 2: open circle), ZnO nanorods decorated with CdSe QDs (curve 3: filled triangle), ZnO nanorods decorated with both CdS and CdSe QDs (curve 4: open triangle), ZnO nanorods coated with Al2O3 and then decorated with CdSe QDs (curve 5: filled square), and ZnO nanorods in situ grown in a solution containing CdSe QDs (curve 6: open square).
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Figure 5: J-V characteristics of different QDSC. ZnO nanorods (curve 1: filled circle), ZnO nanorods decorated with CdS QDs (curve 2: open circle), ZnO nanorods decorated with CdSe QDs (curve 3: filled triangle), ZnO nanorods decorated with both CdS and CdSe QDs (curve 4: open triangle), ZnO nanorods coated with Al2O3 and then decorated with CdSe QDs (curve 5: filled square), and ZnO nanorods in situ grown in a solution containing CdSe QDs (curve 6: open square).

Mentions: The photovoltaic performance of QDSCs based on the vertically aligned ZnO NRAs fabricated on Zn substrates and decorated with CdS and CdSe QDs has been evaluated in a photoelectrochemical cell configuration with a liquid electrolyte containing the I3-/I- redox couple with illumination through the Pt-coated FTO glass. The current density-voltage (J-V) characteristics for solar cells assembled from ZnO NRAs with and without QDs, which represent the performance averaged over 3-5 sample preparations are shown in Figure 5. For the non-sensitized ZnO NRAs based solar cells (curve 1 in Figure 5), the open-circuit voltage (VOC) and short circuit current (JSC) are low. The solar cells decorated with CdSe QDs (curve 3) perform better than those with CdS QDs (curve 2) in terms of the open-circuit voltage and the short-circuit current density, resulting in higher power conversion efficiency (0.46% for CdSe vs. 0.29% for CdS), which is attributed to the broader light absorption of CdSe compared with that of CdS (Figure 4). On the other hand, the FF of CdSe QDs based solar cells is smaller than that of CdS based solar cells, which can be related to the different electron recombination mechanism for the ZnO/CdS and ZnO/CdSe electrodes [27]. At the same time, as CdS solar cells present lower photocurrents, the voltage drop in the series resistance is lower for this type of solar cells, which also enhance the FF. The best performance has been achieved for ZnO nanorods simultaneously decorated with both CdS and CdSe QDs (curve 4), with VOC of 0.68 V and JSC of 4.36 mA/cm2. This shows an advantage of synergetic employment of different types of QDs as it has been discussed recently [12,28]. The performance of the CdSe QD decorated solar cell could be further improved by introducing an ultrathin (~2 nm) layer of Al2O3 grown by ALD on the surface of ZnO nanorods prior to their decoration with QDs. The deposition of Al2O3 shell resulted in a slight increase in VOC and decrease in JSC (curve 5 in Figure 5). However, the FF significantly improved from 0.24 to 0.55, leading to about 50% increase in power conversion efficiency from 0.46 to 0.99%. The increase in VOC has been attributed to the reduction of the electron recombination at the semiconductor/electrolyte interface with the passivation of the recombination sites at the ZnO surface by the Al2O3 coating, while the decrease in JSC resulted from partial inhibition of the electron injection at the semiconductor/QD interfaces [4,29]. Besides, the charge transfer at the Zn/electrolyte interface has been retarded resulting in a platform of the J-V curve for the lower potentials. Accordingly, an intimate contact between the ZnO NRAs and the CdSe QDs (as for the ZnO NRAs in situ grown in the presence of CdSe QDs which are presented in Figure 3c,d) could lead to an increase in VOC and FF due to the eliminated recombination sites at the ZnO/CdSe interface. Indeed this is observed in Figure 5 (curve 6), where VOC has further increased to 0.72 V without significant change in JSC (~2.81 mA/cm2). The performance characteristics of the solar cells illustrated in Figure 5 are summarized in Table 1.


Facile solution growth of vertically aligned ZnO nanorods sensitized with aqueous CdS and CdSe quantum dots for photovoltaic applications.

Luan C, Vaneski A, Susha AS, Xu X, Wang HE, Chen X, Xu J, Zhang W, Lee CS, Rogach AL, Zapien JA - Nanoscale Res Lett (2011)

J-V characteristics of different QDSC. ZnO nanorods (curve 1: filled circle), ZnO nanorods decorated with CdS QDs (curve 2: open circle), ZnO nanorods decorated with CdSe QDs (curve 3: filled triangle), ZnO nanorods decorated with both CdS and CdSe QDs (curve 4: open triangle), ZnO nanorods coated with Al2O3 and then decorated with CdSe QDs (curve 5: filled square), and ZnO nanorods in situ grown in a solution containing CdSe QDs (curve 6: open square).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211429&req=5

Figure 5: J-V characteristics of different QDSC. ZnO nanorods (curve 1: filled circle), ZnO nanorods decorated with CdS QDs (curve 2: open circle), ZnO nanorods decorated with CdSe QDs (curve 3: filled triangle), ZnO nanorods decorated with both CdS and CdSe QDs (curve 4: open triangle), ZnO nanorods coated with Al2O3 and then decorated with CdSe QDs (curve 5: filled square), and ZnO nanorods in situ grown in a solution containing CdSe QDs (curve 6: open square).
Mentions: The photovoltaic performance of QDSCs based on the vertically aligned ZnO NRAs fabricated on Zn substrates and decorated with CdS and CdSe QDs has been evaluated in a photoelectrochemical cell configuration with a liquid electrolyte containing the I3-/I- redox couple with illumination through the Pt-coated FTO glass. The current density-voltage (J-V) characteristics for solar cells assembled from ZnO NRAs with and without QDs, which represent the performance averaged over 3-5 sample preparations are shown in Figure 5. For the non-sensitized ZnO NRAs based solar cells (curve 1 in Figure 5), the open-circuit voltage (VOC) and short circuit current (JSC) are low. The solar cells decorated with CdSe QDs (curve 3) perform better than those with CdS QDs (curve 2) in terms of the open-circuit voltage and the short-circuit current density, resulting in higher power conversion efficiency (0.46% for CdSe vs. 0.29% for CdS), which is attributed to the broader light absorption of CdSe compared with that of CdS (Figure 4). On the other hand, the FF of CdSe QDs based solar cells is smaller than that of CdS based solar cells, which can be related to the different electron recombination mechanism for the ZnO/CdS and ZnO/CdSe electrodes [27]. At the same time, as CdS solar cells present lower photocurrents, the voltage drop in the series resistance is lower for this type of solar cells, which also enhance the FF. The best performance has been achieved for ZnO nanorods simultaneously decorated with both CdS and CdSe QDs (curve 4), with VOC of 0.68 V and JSC of 4.36 mA/cm2. This shows an advantage of synergetic employment of different types of QDs as it has been discussed recently [12,28]. The performance of the CdSe QD decorated solar cell could be further improved by introducing an ultrathin (~2 nm) layer of Al2O3 grown by ALD on the surface of ZnO nanorods prior to their decoration with QDs. The deposition of Al2O3 shell resulted in a slight increase in VOC and decrease in JSC (curve 5 in Figure 5). However, the FF significantly improved from 0.24 to 0.55, leading to about 50% increase in power conversion efficiency from 0.46 to 0.99%. The increase in VOC has been attributed to the reduction of the electron recombination at the semiconductor/electrolyte interface with the passivation of the recombination sites at the ZnO surface by the Al2O3 coating, while the decrease in JSC resulted from partial inhibition of the electron injection at the semiconductor/QD interfaces [4,29]. Besides, the charge transfer at the Zn/electrolyte interface has been retarded resulting in a platform of the J-V curve for the lower potentials. Accordingly, an intimate contact between the ZnO NRAs and the CdSe QDs (as for the ZnO NRAs in situ grown in the presence of CdSe QDs which are presented in Figure 3c,d) could lead to an increase in VOC and FF due to the eliminated recombination sites at the ZnO/CdSe interface. Indeed this is observed in Figure 5 (curve 6), where VOC has further increased to 0.72 V without significant change in JSC (~2.81 mA/cm2). The performance characteristics of the solar cells illustrated in Figure 5 are summarized in Table 1.

Bottom Line: Vertically aligned single crystalline ZnO nanorod arrays, approximately 3 μm in length and 50-450 nm in diameter are grown by a simple solution approach on a Zn foil substrate.A thin Al2O3 layer deposited prior to quantum dot anchoring successfully acts as a barrier inhibiting electron recombination at the Zn/ZnO/electrolyte interface, resulting in power conversion efficiency of approximately 1% with an improved fill factor of 0.55.The in situ growth of ZnO nanorod arrays in a solution containing CdSe quantum dots provides better contact between two materials resulting in enhanced open circuit voltage.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics and Materials Science, City University of Hong Kong, Kowloon, Hong Kong SAR. andrey.rogach@cityu.edu.hk.

ABSTRACT
Vertically aligned single crystalline ZnO nanorod arrays, approximately 3 μm in length and 50-450 nm in diameter are grown by a simple solution approach on a Zn foil substrate. CdS and CdSe colloidal quantum dots are assembled onto ZnO nanorods array using water-soluble nanocrystals capped as-synthesized with a short-chain bifuncional linker thioglycolic acid. The solar cells co-sensitized with both CdS and CdSe quantum dots demonstrate superior efficiency compared with the cells using only one type of quantum dots. A thin Al2O3 layer deposited prior to quantum dot anchoring successfully acts as a barrier inhibiting electron recombination at the Zn/ZnO/electrolyte interface, resulting in power conversion efficiency of approximately 1% with an improved fill factor of 0.55. The in situ growth of ZnO nanorod arrays in a solution containing CdSe quantum dots provides better contact between two materials resulting in enhanced open circuit voltage.

No MeSH data available.