Proceedings of 6th International Conference on Hybrid and Organic Photovoltaics (HOPV14)
Publication date: 1st March 2014
ZnSe quantum dots (QDs) with higher band gaps ranging from 2.8–3.4 eV (bulk ZnSe having a band gap of 2.7 eV) are promising fluorescent materials with emission region from UV to blue. While Zn-based doped QDs have the advantages of low toxicity, large Stocks Shift, high PL conversion efficiency (>40%) and enhanced thermal and environmental stability.1 Therefore, they show potential applications in light-emitting diodes,2 photovoltaic solar cells,3 and biological sensors.4
Herein, ZnSe and Mn:ZnSe quantum dots have been successfully synthesized in aqueous media by a simple low-cost method using thiol-containing ligands (mercaptoacetic acid(TGA), 3-Mercaptopropionic acid(MPA)) as capping reagent. When the molar ratio of Zn:Se:TGA in the solution is 1:0.25:2.5, or the molar ration of Zn:Mn:Se:MPA is 1:0.5:1.1:10, high optical performance quantum dots could be yielded. After irradiated for 4 hours under UV light, the resulting ZnSe QDs show emission peaked at 411 nm with FWHM of 25 nm. While in the case of Mn:ZnSe QDs, the original bandgap emission of ZnSe QDs is quenched almost completely, accompanied with a newly emerged emission band peak at 591 nm with FWHM of 57 nm, which could be ascribed to the 4T1–6A1 transition of the Mn2+ doping centers. According to TEM measurements, the average diameters of ZnSe and Mn:ZnSe QDs are both found to be 3-5 nm with a high degree of crystallinity. (111), (220) and (311) planes are displayed in their XRD patterns, indicating that both the two kinds of QDs were of cubic phases, and the manganese dopant should be incorporated in the ZnSe matrix rather than at the surface. These efficient, colortunable, ZnSe QDs and Mn:ZnSe QDs could be synthesized via careful control on the experimental parameters, including reaction time, pH values, UV irradiation time, concentration of Mn cations. The obtained ZnSe QDs and Mn:ZnSe QDs have higher fluorescence performance The energy level structural models explain the process of the formation of fluorescence to enhance the light-harvesting ability in the short-wavelength range in photovoltaic devices.
Fig. 1 UV-vis and PL emission spectra of the obtained ZnSe and Mn:ZnSe quantum dots.
1. Mirov, S. B.; Fedorov, V. V.; Graham, K.; Moskalev, I. S., Erbium fiber laser-pumped continuous-wave microchip Cr2+: ZnS and Cr2+: ZnSe lasers. Opt. Lett. 2002, 27, 909-911. 2. Chang, J. Y.; Su, L. F.; Li, C. H.; Chang, C. C.; Lin, J. M., Efficient "green" quantum dot-sensitized solar cells based on Cu2S-CuInS2-ZnSe architecture. Chem Commun (Camb) 2012, 48, 4848-50. 3. Maity, A. R.; Palmal, S.; Basiruddin, S. K.; Karan, N. S.; Sarkar, S.; Pradhan, N.; Jana, N. R., Doped semiconductor nanocrystal based fluorescent cellular imaging probes. Nanoscale 2013, 5, 5506-5513. 4. Cheng, D.C.; Hao, H.C.; Zhang, M.; Shi, W.; Lu, M., Improving Si solar cell performance using Mn:ZnSe quantum dot-doped PLMA thin film. Nanoscale Res. Lett. 2013, 8, 291-295.
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