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Improved conversion efficiency of Ag2S quantum dot-sensitized solar cells based on TiO2 nanotubes with a ZnO recombination barrier layer.

Chen C, Xie Y, Ali G, Yoo SH, Cho SO - Nanoscale Res Lett (2011)

Bottom Line: We improve the conversion efficiency of Ag2S quantum dot (QD)-sensitized TiO2 nanotube-array electrodes by chemically depositing ZnO recombination barrier layer on plain TiO2 nanotube-array electrodes.It is found that for the prepared electrodes, with increasing the cycles of Ag2S deposition, the photocurrent density and the conversion efficiency increase.In addition, as compared to the Ag2S QD-sensitized TiO2 nanotube-array electrode without the ZnO layers, the conversion efficiency of the electrode with the ZnO layers increases significantly due to the formation of efficient recombination layer between the TiO2 nanotube array and electrolyte.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology (KAIST), 373-1 Guseong, Yuseong, Daejeon 305-701, Republic of Korea. socho@kaist.ac.kr.

ABSTRACT
We improve the conversion efficiency of Ag2S quantum dot (QD)-sensitized TiO2 nanotube-array electrodes by chemically depositing ZnO recombination barrier layer on plain TiO2 nanotube-array electrodes. The optical properties, structural properties, compositional analysis, and photoelectrochemistry properties of prepared electrodes have been investigated. It is found that for the prepared electrodes, with increasing the cycles of Ag2S deposition, the photocurrent density and the conversion efficiency increase. In addition, as compared to the Ag2S QD-sensitized TiO2 nanotube-array electrode without the ZnO layers, the conversion efficiency of the electrode with the ZnO layers increases significantly due to the formation of efficient recombination layer between the TiO2 nanotube array and electrolyte.

No MeSH data available.


The photoconversion efficiencies of the Ag2S(8)/ZnO/TNT and Ag2S(8)/TNT electrodes.
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Figure 7: The photoconversion efficiencies of the Ag2S(8)/ZnO/TNT and Ag2S(8)/TNT electrodes.

Mentions: Figure 7 shows the photoconversion efficiency η as a function of applied potential (vs. Ag/AgCl) for the Ag2S(8)/ZnO/TNT and Ag2S(8)/TNT electrodes under UV-vis light irradiation. The efficiency η is calculated as [39], η (%) = [(total power output-electric power input)/light power input] × 100 = jp [(Erev /Eapp/)/I0] × 100, where jp is the photocurrent density (milliamperes per square centimeter), jp × Erev is the total power output, jp × Eapp is the electrical power input, and I0 is the power density of incident light (milliwatts per square centimeter). Erev is the standard state-reversible potential, which is 1.23 V/NHE. The applied potential is Eapp = Emeans - Eaoc, where Emeans is the electrode potential (vs. Ag/AgCl) of the working electrode at which photocurrent was measured under illumination and Eaoc is the electrode potential (vs. Ag/AgCl) of the same working electrode under open circuit conditions, under the same illumination, and in the same electrolyte. It can be clearly seen from Figure 7 that the Ag2S(8)/ZnO/TNT electrode shows a higher photoconversion efficiency compared to the Ag2S(8)/TNT electrode with a ZnO layer for an applied potential. In particular, a maximum photoconversion efficiency of 0.28% was obtained at an applied potential of -0.67 V vs. Ag/AgCl for the Ag2S(8)/ZnO/TNT electrode, while it was 0.22% for the Ag2S(8)/TNT electrode at an applied potential of -0.67 V. The maximum photoconversion efficiency of the Ag2S(8)/ZnO/TNT electrode is about 1.3 times that of the Ag2S(8)/TNT electrode. However, it should be noted that the efficiency of the Ag2S-sensitized TNT electrode is worse than the value obtained from Ag2S QD-sensitized nanocrystalline TiO2 film, which was recently reported by Tubtimtae et al. [25]. The main reason may be due to the different architecture of TiO2 electrode. Ag2S QDs cannot be deposited in large numbers on the inner surface of TNTs due to the limited space in TNTs, while the number of Ag2S QDs deposited on the surface of nanocrystalline TiO2 film is almost not limited. This means that compared to the TNTs, more Ag2S QDs can be deposited on nanocrystalline TiO2 film and absorb more light leading to a higher photocurrent. Besides, in our case, we use TNT electrode and 1 M Na2S electrolyte. However, Tubtimtae et al. used nanocrystalline TiO2 film and a polysulfide electrolyte consisted of 0.5 M Na2S, 2 M S, 0.2 M KCl, and 0.5 M NaOH in methanol/water. Clearly, the electrolyte will affect the performance of the devices. Moreover, the photocurrent measurements are performed under different conditions. A three-electrode configuration was employed in our experiments. However, a two-electrode configuration was used in the experiments of Tubtimtae et al. In addition, our results show that the efficiency obtained from Ag2S-sensitized TNTs is also lower than that of CdS-sensitized TiO2 electrode [31]. The main reason for this may be that the CB level of Ag2S is lower than that of TiO2 as shown in Figure 6a[40], but the CB level of CdS is higher than that of TiO2. Therefore, the electron transfer is more efficient in CdS/TNT solar cells. The comparison of our current experiments with those by Tubtimtae et al. indicates that there is still much scope for improving the performance of the Ag2S-sensitied ZnO/TNT electrode. Nevertheless, our results show that the ZnO layer leads to an increased η.


Improved conversion efficiency of Ag2S quantum dot-sensitized solar cells based on TiO2 nanotubes with a ZnO recombination barrier layer.

Chen C, Xie Y, Ali G, Yoo SH, Cho SO - Nanoscale Res Lett (2011)

The photoconversion efficiencies of the Ag2S(8)/ZnO/TNT and Ag2S(8)/TNT electrodes.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211883&req=5

Figure 7: The photoconversion efficiencies of the Ag2S(8)/ZnO/TNT and Ag2S(8)/TNT electrodes.
Mentions: Figure 7 shows the photoconversion efficiency η as a function of applied potential (vs. Ag/AgCl) for the Ag2S(8)/ZnO/TNT and Ag2S(8)/TNT electrodes under UV-vis light irradiation. The efficiency η is calculated as [39], η (%) = [(total power output-electric power input)/light power input] × 100 = jp [(Erev /Eapp/)/I0] × 100, where jp is the photocurrent density (milliamperes per square centimeter), jp × Erev is the total power output, jp × Eapp is the electrical power input, and I0 is the power density of incident light (milliwatts per square centimeter). Erev is the standard state-reversible potential, which is 1.23 V/NHE. The applied potential is Eapp = Emeans - Eaoc, where Emeans is the electrode potential (vs. Ag/AgCl) of the working electrode at which photocurrent was measured under illumination and Eaoc is the electrode potential (vs. Ag/AgCl) of the same working electrode under open circuit conditions, under the same illumination, and in the same electrolyte. It can be clearly seen from Figure 7 that the Ag2S(8)/ZnO/TNT electrode shows a higher photoconversion efficiency compared to the Ag2S(8)/TNT electrode with a ZnO layer for an applied potential. In particular, a maximum photoconversion efficiency of 0.28% was obtained at an applied potential of -0.67 V vs. Ag/AgCl for the Ag2S(8)/ZnO/TNT electrode, while it was 0.22% for the Ag2S(8)/TNT electrode at an applied potential of -0.67 V. The maximum photoconversion efficiency of the Ag2S(8)/ZnO/TNT electrode is about 1.3 times that of the Ag2S(8)/TNT electrode. However, it should be noted that the efficiency of the Ag2S-sensitized TNT electrode is worse than the value obtained from Ag2S QD-sensitized nanocrystalline TiO2 film, which was recently reported by Tubtimtae et al. [25]. The main reason may be due to the different architecture of TiO2 electrode. Ag2S QDs cannot be deposited in large numbers on the inner surface of TNTs due to the limited space in TNTs, while the number of Ag2S QDs deposited on the surface of nanocrystalline TiO2 film is almost not limited. This means that compared to the TNTs, more Ag2S QDs can be deposited on nanocrystalline TiO2 film and absorb more light leading to a higher photocurrent. Besides, in our case, we use TNT electrode and 1 M Na2S electrolyte. However, Tubtimtae et al. used nanocrystalline TiO2 film and a polysulfide electrolyte consisted of 0.5 M Na2S, 2 M S, 0.2 M KCl, and 0.5 M NaOH in methanol/water. Clearly, the electrolyte will affect the performance of the devices. Moreover, the photocurrent measurements are performed under different conditions. A three-electrode configuration was employed in our experiments. However, a two-electrode configuration was used in the experiments of Tubtimtae et al. In addition, our results show that the efficiency obtained from Ag2S-sensitized TNTs is also lower than that of CdS-sensitized TiO2 electrode [31]. The main reason for this may be that the CB level of Ag2S is lower than that of TiO2 as shown in Figure 6a[40], but the CB level of CdS is higher than that of TiO2. Therefore, the electron transfer is more efficient in CdS/TNT solar cells. The comparison of our current experiments with those by Tubtimtae et al. indicates that there is still much scope for improving the performance of the Ag2S-sensitied ZnO/TNT electrode. Nevertheless, our results show that the ZnO layer leads to an increased η.

Bottom Line: We improve the conversion efficiency of Ag2S quantum dot (QD)-sensitized TiO2 nanotube-array electrodes by chemically depositing ZnO recombination barrier layer on plain TiO2 nanotube-array electrodes.It is found that for the prepared electrodes, with increasing the cycles of Ag2S deposition, the photocurrent density and the conversion efficiency increase.In addition, as compared to the Ag2S QD-sensitized TiO2 nanotube-array electrode without the ZnO layers, the conversion efficiency of the electrode with the ZnO layers increases significantly due to the formation of efficient recombination layer between the TiO2 nanotube array and electrolyte.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology (KAIST), 373-1 Guseong, Yuseong, Daejeon 305-701, Republic of Korea. socho@kaist.ac.kr.

ABSTRACT
We improve the conversion efficiency of Ag2S quantum dot (QD)-sensitized TiO2 nanotube-array electrodes by chemically depositing ZnO recombination barrier layer on plain TiO2 nanotube-array electrodes. The optical properties, structural properties, compositional analysis, and photoelectrochemistry properties of prepared electrodes have been investigated. It is found that for the prepared electrodes, with increasing the cycles of Ag2S deposition, the photocurrent density and the conversion efficiency increase. In addition, as compared to the Ag2S QD-sensitized TiO2 nanotube-array electrode without the ZnO layers, the conversion efficiency of the electrode with the ZnO layers increases significantly due to the formation of efficient recombination layer between the TiO2 nanotube array and electrolyte.

No MeSH data available.