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Synthesis of CuInS2 quantum dots using polyetheramine as solvent.

Shei SC, Chiang WJ, Chang SJ - Nanoscale Res Lett (2015)

Bottom Line: An excess of group VI elements facilitated precipitation, whereas an excess of group I elements resulted in CuInS2 QDs with high photoluminescence quantum yield.Our results demonstrate that the band gap of the CuInS2 QDs is tunable with size as well as the composition of the reactant.We also determined some important physical parameters such as the band gaps and energy levels of this system, which are crucial for the application of CuInS2 nanocrystals.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical Engineering, National University of Tainan, Tainan, 70005 Taiwan.

ABSTRACT
This paper presents a facile solvothermal method of synthesizing copper indium sulfide (CuInS2) quantum dots (QDs) via a non-coordinated system using polyetheramine as a solvent. The structural and optical properties of the resulting CuInS2 QDs were investigated using composition analysis, absorption spectroscopy, and emission spectroscopy. We employed molar ratios of I, III, and VI group elements to control the structure of CuInS2 QDs. An excess of group VI elements facilitated precipitation, whereas an excess of group I elements resulted in CuInS2 QDs with high photoluminescence quantum yield. The emission wavelength and photoluminescence quantum yield could also be modulated by controlling the composition ratio of Cu and In in the injection stock solution. An increase in the portion of S shifted the emission wavelength of the QDs to a shorter wavelength and increased the photoluminescence quantum yield. Our results demonstrate that the band gap of the CuInS2 QDs is tunable with size as well as the composition of the reactant. The photoluminescence quantum yield of the CuInS2 QDs ranged between 0.7% and 8.8% at 250°C. We also determined some important physical parameters such as the band gaps and energy levels of this system, which are crucial for the application of CuInS2 nanocrystals.

No MeSH data available.


TEM images of CIS QDs synthesized under reaction times of (a) 1 and (b) 8 h.
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Fig6: TEM images of CIS QDs synthesized under reaction times of (a) 1 and (b) 8 h.

Mentions: Figure 4 presents the PL emission spectra of CIS QDs as a function of solvothermal growth time. CIS QDs were solvothermally synthesized at a fixed temperature of 150°C and Cu/In molar ratios of 1/1 for durations of 1, 2, 3, 4, 5, 6, 7, and 8 h, respectively. All CIS QDs presented orange color emissions (550 to 600 nm) with the peak wavelength slightly red-shifted in cases of longer growth time. The bandwidth (FWHM) of the emission of all CIS QDs fell within the range 98 to 105 nm, showing a tendency to form a broader emission band with longer growth time. Figure 5 presents the absorption spectra of CIS QDs grown at a fixed temperature of 150°C and Cu/In molar ratios of 1/1 for durations of 1, 2, 3, 4, 5, 6, 7, and 8 h, respectively. The absorption spectra gradually shifted to longer wavelengths with reaction time due to the growth of particles. Among various absorption spectrum, there is a long tail for the absorption profile due to the defect states (donors and acceptors) within the band gap. As reported in previous studies, distinct excitonic absorption features were not observed in the present CIS QDs. Such unresolved absorption features have been attributed to individual as well as combined factors, including a broad size distribution, unequal composition distribution, and the unique electronic properties of CIS QDs. The radiative recombination of excited electron-hole pairs in these kinds of QDs is associated with defect states (donors and acceptors) within the band gap, referred to as donor-acceptor pair (DAP) recombination [20-24]. The fact that many types of donor and acceptor sites exist suggests that the above defect energy levels may vary somewhat with QD size. Specifically, this would entail a shift in the donor and acceptor levels toward the edges of the conduction band (CB) and valence band (VB). Thus, it can be stated that a wide QD size distribution in the CIS QD ensemble is at least one of the reasons for the unresolved absorption peaks appearing in Figure 5. The normalized PL emission spectra of QDs are also presented in Figure 4, where a similar red shift in the absorption spectra with a decrease in QD size can be observed. The figure specifically shows a shift in peak emission wavelength from 550 nm (for 1-h QD) to 600 nm (8-h QD). This kind of shift in size-dependent emission toward the red in size sorted QD fractions may provide additional support for the supposition that the energy spacing between donor and acceptor levels increases with an increase in the size of the QDs. Broadband emissions are characteristic of DAP recombination resulting from a combination of strong electron-phonon interaction and a wide donor–acceptor distance distribution [19], which can be ascribed to size and/or compositional inhomogeneity in the QDs. Therefore, the nature of DAP recombination is likely the sole factor responsible for the broadness of CIS QD emissions, if the chemical composition of individual QDs is assumed to be homogeneous. Figure 6 presents TEM images of CIS QDs grown for 1 and 8 h, both of which are not monodispersed. The sizes of QDs produced through a 1-h reaction were distributed in the range of 2 to 10 nm, while those produced over a period of 8 h grew only slightly more to 8 to 16 nm, which is the most appropriate shell phase for the surface passivation of chalcopyrite I-III-VI QDs.Figure 4


Synthesis of CuInS2 quantum dots using polyetheramine as solvent.

Shei SC, Chiang WJ, Chang SJ - Nanoscale Res Lett (2015)

TEM images of CIS QDs synthesized under reaction times of (a) 1 and (b) 8 h.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4385220&req=5

Fig6: TEM images of CIS QDs synthesized under reaction times of (a) 1 and (b) 8 h.
Mentions: Figure 4 presents the PL emission spectra of CIS QDs as a function of solvothermal growth time. CIS QDs were solvothermally synthesized at a fixed temperature of 150°C and Cu/In molar ratios of 1/1 for durations of 1, 2, 3, 4, 5, 6, 7, and 8 h, respectively. All CIS QDs presented orange color emissions (550 to 600 nm) with the peak wavelength slightly red-shifted in cases of longer growth time. The bandwidth (FWHM) of the emission of all CIS QDs fell within the range 98 to 105 nm, showing a tendency to form a broader emission band with longer growth time. Figure 5 presents the absorption spectra of CIS QDs grown at a fixed temperature of 150°C and Cu/In molar ratios of 1/1 for durations of 1, 2, 3, 4, 5, 6, 7, and 8 h, respectively. The absorption spectra gradually shifted to longer wavelengths with reaction time due to the growth of particles. Among various absorption spectrum, there is a long tail for the absorption profile due to the defect states (donors and acceptors) within the band gap. As reported in previous studies, distinct excitonic absorption features were not observed in the present CIS QDs. Such unresolved absorption features have been attributed to individual as well as combined factors, including a broad size distribution, unequal composition distribution, and the unique electronic properties of CIS QDs. The radiative recombination of excited electron-hole pairs in these kinds of QDs is associated with defect states (donors and acceptors) within the band gap, referred to as donor-acceptor pair (DAP) recombination [20-24]. The fact that many types of donor and acceptor sites exist suggests that the above defect energy levels may vary somewhat with QD size. Specifically, this would entail a shift in the donor and acceptor levels toward the edges of the conduction band (CB) and valence band (VB). Thus, it can be stated that a wide QD size distribution in the CIS QD ensemble is at least one of the reasons for the unresolved absorption peaks appearing in Figure 5. The normalized PL emission spectra of QDs are also presented in Figure 4, where a similar red shift in the absorption spectra with a decrease in QD size can be observed. The figure specifically shows a shift in peak emission wavelength from 550 nm (for 1-h QD) to 600 nm (8-h QD). This kind of shift in size-dependent emission toward the red in size sorted QD fractions may provide additional support for the supposition that the energy spacing between donor and acceptor levels increases with an increase in the size of the QDs. Broadband emissions are characteristic of DAP recombination resulting from a combination of strong electron-phonon interaction and a wide donor–acceptor distance distribution [19], which can be ascribed to size and/or compositional inhomogeneity in the QDs. Therefore, the nature of DAP recombination is likely the sole factor responsible for the broadness of CIS QD emissions, if the chemical composition of individual QDs is assumed to be homogeneous. Figure 6 presents TEM images of CIS QDs grown for 1 and 8 h, both of which are not monodispersed. The sizes of QDs produced through a 1-h reaction were distributed in the range of 2 to 10 nm, while those produced over a period of 8 h grew only slightly more to 8 to 16 nm, which is the most appropriate shell phase for the surface passivation of chalcopyrite I-III-VI QDs.Figure 4

Bottom Line: An excess of group VI elements facilitated precipitation, whereas an excess of group I elements resulted in CuInS2 QDs with high photoluminescence quantum yield.Our results demonstrate that the band gap of the CuInS2 QDs is tunable with size as well as the composition of the reactant.We also determined some important physical parameters such as the band gaps and energy levels of this system, which are crucial for the application of CuInS2 nanocrystals.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical Engineering, National University of Tainan, Tainan, 70005 Taiwan.

ABSTRACT
This paper presents a facile solvothermal method of synthesizing copper indium sulfide (CuInS2) quantum dots (QDs) via a non-coordinated system using polyetheramine as a solvent. The structural and optical properties of the resulting CuInS2 QDs were investigated using composition analysis, absorption spectroscopy, and emission spectroscopy. We employed molar ratios of I, III, and VI group elements to control the structure of CuInS2 QDs. An excess of group VI elements facilitated precipitation, whereas an excess of group I elements resulted in CuInS2 QDs with high photoluminescence quantum yield. The emission wavelength and photoluminescence quantum yield could also be modulated by controlling the composition ratio of Cu and In in the injection stock solution. An increase in the portion of S shifted the emission wavelength of the QDs to a shorter wavelength and increased the photoluminescence quantum yield. Our results demonstrate that the band gap of the CuInS2 QDs is tunable with size as well as the composition of the reactant. The photoluminescence quantum yield of the CuInS2 QDs ranged between 0.7% and 8.8% at 250°C. We also determined some important physical parameters such as the band gaps and energy levels of this system, which are crucial for the application of CuInS2 nanocrystals.

No MeSH data available.