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Rough gold films as broadband absorbers for plasmonic enhancement of TiO 2 photocurrent over 400 – 800   nm

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ABSTRACT

Recent years have witnessed an increasing interest in highly-efficient absorbers of visible light for the conversion of solar energy into electrochemical energy. This study presents a TiO2-Au bilayer that consists of a rough Au film under a TiO2 film, which aims to enhance the photocurrent of TiO2 over the whole visible region and may be the first attempt to use rough Au films to sensitize TiO2. Experiments show that the bilayer structure gives the optimal optical and photoelectrochemical performance when the TiO2 layer is 30 nm thick and the Au film is 100 nm, measuring the absorption 80–90% over 400–800 nm and the photocurrent intensity of 15 μA·cm−2, much better than those of the TiO2-AuNP hybrid (i.e., Au nanoparticle covered by the TiO2 film) and the bare TiO2 film. The superior properties of the TiO2-Au bilayer can be attributed to the rough Au film as the plasmonic visible-light sensitizer and the photoactive TiO2 film as the electron accepter. As the Au film is fully covered by the TiO2 film, the TiO2-Au bilayer avoids the photocorrosion and leakage of Au materials and is expected to be stable for long-term operation, making it an excellent photoelectrode for the conversion of solar energy into electrochemical energy in the applications of water splitting, photocatalysis and photosynthesis.

No MeSH data available.


(a) I-t plots and (b) photocurrent densities of the TiO2-Au bilayer samples with the TiO2 thicknesses of 0, 5, 10, 20, 30 and 50 nm, here the sample of 0 nm represents the rough TiO2 film itself; (c) I-t plots under the irradiation of different monochromatic wavelengths; and (d) action spectra (i.e., photocurrent versus wavelength) of the TiO2-Au bilayer (red line) and its constituent layers – the bare TiO2 film (black line) and the bare Au film (blue line), here the TiO2 film is always 30 nm thick.
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f4: (a) I-t plots and (b) photocurrent densities of the TiO2-Au bilayer samples with the TiO2 thicknesses of 0, 5, 10, 20, 30 and 50 nm, here the sample of 0 nm represents the rough TiO2 film itself; (c) I-t plots under the irradiation of different monochromatic wavelengths; and (d) action spectra (i.e., photocurrent versus wavelength) of the TiO2-Au bilayer (red line) and its constituent layers – the bare TiO2 film (black line) and the bare Au film (blue line), here the TiO2 film is always 30 nm thick.

Mentions: The results of I-t measurements are plotted in Fig. 4a for the TiO2-Au bilayer samples with different TiO2 film thicknesses. It is seen that the photocurrents respond immediately and repeatedly to the turning on and off of light source. Figure 4b plots the measured photocurrent density as a function of the TiO2 thickness, showing the maximum 12.4 μA·cm−2 at 30 nm. Therefore, the TiO2-Au bilayer sample with the 30-nm-thick TiO2 film has the highest photocurrent, this sample is named as the “optimal bilayer sample”. To further investigate the wavelength dependence, the optimal bilayer sample is illuminated with a broadband visible light source (λ ≥ 400 nm) that delivers a total power of ~300 mW/cm2 (see Fig. S3a of Supplementary Information for the calibrated emission spectrum). The light source employs a series of narrow-band optical filters to filter the broadband light into roughly monochromatic light. The source intensity as a function of the wavelength using the optical filters is plotted in Fig. S3b, agreeing with the spectrum of visible light source (see Fig. S3a)27. The I-t plots of the optimal bilayer sample are shown in Fig. 4c for the wavelengths of 420, 450, 475, 500, 520, 550, 600 and 650 nm, respectively. As a supplementary, the I-t plots of the bare TiO2 film and the TiO2-AuNP hybrid are also shown in Fig. S3c,d, respectively. For quantitative comparison, the action spectra (i.e., photocurrent density versus light wavelength) are plotted in Fig. 4d for the optimal bilayer sample and its constituent layers–the 30-nm-thick bare TiO2 film and the bare Au film. It is seen that the bare Au film has almost no response whereas the optimal bilayer sample has the highest result, showing significant enhancement as compared to the bare TiO2 film. For the optimal bilayer sample, the photocurrent density drops quickly when the wavelength goes up to 600 nm and becomes very low afterward. The energy conversion efficiencies of the three samples can also be indicated by the incident photon to current efficiency (IPCE), which are extracted from the measured photocurrents and the incident spectrum. The IPCE of the optimal TiO2-Au bilayer sample reveals a clear enhancement as compared to the bare TiO2 film and the bare Au film, which is consistent with the action spectra plotted in Fig. 4d.


Rough gold films as broadband absorbers for plasmonic enhancement of TiO 2 photocurrent over 400 – 800   nm
(a) I-t plots and (b) photocurrent densities of the TiO2-Au bilayer samples with the TiO2 thicknesses of 0, 5, 10, 20, 30 and 50 nm, here the sample of 0 nm represents the rough TiO2 film itself; (c) I-t plots under the irradiation of different monochromatic wavelengths; and (d) action spectra (i.e., photocurrent versus wavelength) of the TiO2-Au bilayer (red line) and its constituent layers – the bare TiO2 film (black line) and the bare Au film (blue line), here the TiO2 film is always 30 nm thick.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5016800&req=5

f4: (a) I-t plots and (b) photocurrent densities of the TiO2-Au bilayer samples with the TiO2 thicknesses of 0, 5, 10, 20, 30 and 50 nm, here the sample of 0 nm represents the rough TiO2 film itself; (c) I-t plots under the irradiation of different monochromatic wavelengths; and (d) action spectra (i.e., photocurrent versus wavelength) of the TiO2-Au bilayer (red line) and its constituent layers – the bare TiO2 film (black line) and the bare Au film (blue line), here the TiO2 film is always 30 nm thick.
Mentions: The results of I-t measurements are plotted in Fig. 4a for the TiO2-Au bilayer samples with different TiO2 film thicknesses. It is seen that the photocurrents respond immediately and repeatedly to the turning on and off of light source. Figure 4b plots the measured photocurrent density as a function of the TiO2 thickness, showing the maximum 12.4 μA·cm−2 at 30 nm. Therefore, the TiO2-Au bilayer sample with the 30-nm-thick TiO2 film has the highest photocurrent, this sample is named as the “optimal bilayer sample”. To further investigate the wavelength dependence, the optimal bilayer sample is illuminated with a broadband visible light source (λ ≥ 400 nm) that delivers a total power of ~300 mW/cm2 (see Fig. S3a of Supplementary Information for the calibrated emission spectrum). The light source employs a series of narrow-band optical filters to filter the broadband light into roughly monochromatic light. The source intensity as a function of the wavelength using the optical filters is plotted in Fig. S3b, agreeing with the spectrum of visible light source (see Fig. S3a)27. The I-t plots of the optimal bilayer sample are shown in Fig. 4c for the wavelengths of 420, 450, 475, 500, 520, 550, 600 and 650 nm, respectively. As a supplementary, the I-t plots of the bare TiO2 film and the TiO2-AuNP hybrid are also shown in Fig. S3c,d, respectively. For quantitative comparison, the action spectra (i.e., photocurrent density versus light wavelength) are plotted in Fig. 4d for the optimal bilayer sample and its constituent layers–the 30-nm-thick bare TiO2 film and the bare Au film. It is seen that the bare Au film has almost no response whereas the optimal bilayer sample has the highest result, showing significant enhancement as compared to the bare TiO2 film. For the optimal bilayer sample, the photocurrent density drops quickly when the wavelength goes up to 600 nm and becomes very low afterward. The energy conversion efficiencies of the three samples can also be indicated by the incident photon to current efficiency (IPCE), which are extracted from the measured photocurrents and the incident spectrum. The IPCE of the optimal TiO2-Au bilayer sample reveals a clear enhancement as compared to the bare TiO2 film and the bare Au film, which is consistent with the action spectra plotted in Fig. 4d.

View Article: PubMed Central - PubMed

ABSTRACT

Recent years have witnessed an increasing interest in highly-efficient absorbers of visible light for the conversion of solar energy into electrochemical energy. This study presents a TiO2-Au bilayer that consists of a rough Au film under a TiO2 film, which aims to enhance the photocurrent of TiO2 over the whole visible region and may be the first attempt to use rough Au films to sensitize TiO2. Experiments show that the bilayer structure gives the optimal optical and photoelectrochemical performance when the TiO2 layer is 30 nm thick and the Au film is 100 nm, measuring the absorption 80–90% over 400–800 nm and the photocurrent intensity of 15 μA·cm−2, much better than those of the TiO2-AuNP hybrid (i.e., Au nanoparticle covered by the TiO2 film) and the bare TiO2 film. The superior properties of the TiO2-Au bilayer can be attributed to the rough Au film as the plasmonic visible-light sensitizer and the photoactive TiO2 film as the electron accepter. As the Au film is fully covered by the TiO2 film, the TiO2-Au bilayer avoids the photocorrosion and leakage of Au materials and is expected to be stable for long-term operation, making it an excellent photoelectrode for the conversion of solar energy into electrochemical energy in the applications of water splitting, photocatalysis and photosynthesis.

No MeSH data available.