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One-step synthesis of PbSe-ZnSe composite thin film.

Abe S - Nanoscale Res Lett (2011)

Bottom Line: The XRD result reveals that the solubility limit of Pb in ZnSe is quite narrow, less than 1 mol%, with obvious phase-separation in the composite thin films.A nanoscale elemental mapping of the film containing 5 mol% PbSe indicates that isolated PbSe nanocrystals are dispersed in the ZnSe matrix.The use of a phase-separating PbSe-ZnSe system and HWD techniques enables simple production of the composite package.

View Article: PubMed Central - HTML - PubMed

Affiliation: Research Institute for Electric and Magnetic Materials, Sendai 982-0807, Japan. abe@denjiken.ne.jp.

ABSTRACT
This study investigates the preparation of PbSe-ZnSe composite thin films by simultaneous hot-wall deposition (HWD) from multiple resources. The XRD result reveals that the solubility limit of Pb in ZnSe is quite narrow, less than 1 mol%, with obvious phase-separation in the composite thin films. A nanoscale elemental mapping of the film containing 5 mol% PbSe indicates that isolated PbSe nanocrystals are dispersed in the ZnSe matrix. The optical absorption edge of the composite thin films shifts toward the low-photon-energy region as the PbSe content increases. The use of a phase-separating PbSe-ZnSe system and HWD techniques enables simple production of the composite package.

No MeSH data available.


Optical absorption spectra for PbSe-ZnSe composite thin films.
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Figure 5: Optical absorption spectra for PbSe-ZnSe composite thin films.

Mentions: Figure 5 depicts optical absorption spectra for the PbSe-ZnSe composite thin films. For comparison, the spectrum of a pure ZnSe thin film is also presented in the figure. PbSe and ZnSe have direct band structures [21,22], and an intact absorbance is employed here to exactly evaluate the absorption edge. At a 0 mol% PbSe, the optical absorption edge of ZnSe is clearly observed at 2.7 eV. Weak absorption then broadly appears at a PbSe concentration of 1 mol% in the visible region, together with the optical absorption edge of ZnSe. Such multiple absorptions are also seen in the spectra at concentrations up to 7 mol%, indicating the obvious phase separation of the PbSe-ZnSe system. The broad absorption edge shifts toward the lower-energy region as the PbSe content increases. In particular, onset absorption can be confirmed at approximately 1.0 eV at 16 mol% PbSe, favorably covering the desirable energy region for high conversion efficiency [23]. Therefore, it should be noted that the PbSe-ZnSe composite thin film exhibits the valuable characteristic of vis-NIR absorption. However, it is unclear whether the shift of the optical absorption edge is due to the PbSe nanocrystals, since the mean grain size of the PbSe remains almost the same at 27 nm irrespective of the PbSe content, according to the XRD result (Figure 3) using Scherrer's equation [24]. The minimal appearance of infrared absorption at 16 mol% PbSe strongly suggests that relatively large-scale PbSe grains are partially involved in the composite film, since the energy band gap of bulk PbSe is 0.27 eV [22]. Another TEM image also indicates the presence of relatively large PbSe crystals of approximately 100 nm, even with a small amount of 5 mol% PbSe (not shown here). Hence, the mean grain size of the PbSe is bimodally distributed in the composite. These large-scale PbSe grains probably dominate the full width at half maximum value of the XRD peak, resulting in no obvious relation between the optical absorption shift and the PbSe grain size. The size control of the nanocrystalline PbSe is therefore insufficient in the present study. The substrate temperature thus adopted seems to assist in the aggregation of PbSe nanocrystals. However, a one-step synthesis of the composite package has the potential to lead to low-cost production of next-generation solar cells.


One-step synthesis of PbSe-ZnSe composite thin film.

Abe S - Nanoscale Res Lett (2011)

Optical absorption spectra for PbSe-ZnSe composite thin films.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211412&req=5

Figure 5: Optical absorption spectra for PbSe-ZnSe composite thin films.
Mentions: Figure 5 depicts optical absorption spectra for the PbSe-ZnSe composite thin films. For comparison, the spectrum of a pure ZnSe thin film is also presented in the figure. PbSe and ZnSe have direct band structures [21,22], and an intact absorbance is employed here to exactly evaluate the absorption edge. At a 0 mol% PbSe, the optical absorption edge of ZnSe is clearly observed at 2.7 eV. Weak absorption then broadly appears at a PbSe concentration of 1 mol% in the visible region, together with the optical absorption edge of ZnSe. Such multiple absorptions are also seen in the spectra at concentrations up to 7 mol%, indicating the obvious phase separation of the PbSe-ZnSe system. The broad absorption edge shifts toward the lower-energy region as the PbSe content increases. In particular, onset absorption can be confirmed at approximately 1.0 eV at 16 mol% PbSe, favorably covering the desirable energy region for high conversion efficiency [23]. Therefore, it should be noted that the PbSe-ZnSe composite thin film exhibits the valuable characteristic of vis-NIR absorption. However, it is unclear whether the shift of the optical absorption edge is due to the PbSe nanocrystals, since the mean grain size of the PbSe remains almost the same at 27 nm irrespective of the PbSe content, according to the XRD result (Figure 3) using Scherrer's equation [24]. The minimal appearance of infrared absorption at 16 mol% PbSe strongly suggests that relatively large-scale PbSe grains are partially involved in the composite film, since the energy band gap of bulk PbSe is 0.27 eV [22]. Another TEM image also indicates the presence of relatively large PbSe crystals of approximately 100 nm, even with a small amount of 5 mol% PbSe (not shown here). Hence, the mean grain size of the PbSe is bimodally distributed in the composite. These large-scale PbSe grains probably dominate the full width at half maximum value of the XRD peak, resulting in no obvious relation between the optical absorption shift and the PbSe grain size. The size control of the nanocrystalline PbSe is therefore insufficient in the present study. The substrate temperature thus adopted seems to assist in the aggregation of PbSe nanocrystals. However, a one-step synthesis of the composite package has the potential to lead to low-cost production of next-generation solar cells.

Bottom Line: The XRD result reveals that the solubility limit of Pb in ZnSe is quite narrow, less than 1 mol%, with obvious phase-separation in the composite thin films.A nanoscale elemental mapping of the film containing 5 mol% PbSe indicates that isolated PbSe nanocrystals are dispersed in the ZnSe matrix.The use of a phase-separating PbSe-ZnSe system and HWD techniques enables simple production of the composite package.

View Article: PubMed Central - HTML - PubMed

Affiliation: Research Institute for Electric and Magnetic Materials, Sendai 982-0807, Japan. abe@denjiken.ne.jp.

ABSTRACT
This study investigates the preparation of PbSe-ZnSe composite thin films by simultaneous hot-wall deposition (HWD) from multiple resources. The XRD result reveals that the solubility limit of Pb in ZnSe is quite narrow, less than 1 mol%, with obvious phase-separation in the composite thin films. A nanoscale elemental mapping of the film containing 5 mol% PbSe indicates that isolated PbSe nanocrystals are dispersed in the ZnSe matrix. The optical absorption edge of the composite thin films shifts toward the low-photon-energy region as the PbSe content increases. The use of a phase-separating PbSe-ZnSe system and HWD techniques enables simple production of the composite package.

No MeSH data available.