Effect of oleylamine on microwave synthesized Cu 2 ZnSnS 4 nanocrystals for photovoltaic junctions

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Abstract
Cu2ZnSnS4 (CZTS) with its high absorption coefficient, optimal band gap, and non-toxic, earth-abundant elemental constituents is a promising absorber material for low cost and high-performance photovoltaics. CZTS nanocrystals were prepared by microwave-assisted thermolysis method using ethylene glycol solvent in a rapid and energy efficient process with and without oleylamine as additional capping agent. X-ray diffraction data indicated crystallite sizes of 5 and 12 nm respectively. Raman spectra showed the formation of pure Cu2ZnSnS4 phase in both cases. With pure ethylene glycol solvent, field emission scanning electron microscopy images showed particle sizes around 250 nm, ultraviolet-visible absorption data gave optical band gap of 1.52 eV and Hall measurements yielded electrical resistivity ~70 Ωcm, carrier density ~2.7 × 1016/cm3, and hole mobility ~3.24 cm2/Vs. Adding optimum amount of oleylamine reduced the particle size to 100 nm and lower. The optical band gap reduced to 1.48 eV and electrical resistivity, carrier concentration, and Hall mobility changed to ~5.9 × 104 Ωcm, 2.57 × 1012/cm3, and 4.1 cm2/Vs respectively. A knee voltage of ~0.8 V shown by CZTS/CdS p-n junction indicated that a good Voc can be expected from a solar cell constructed with the CZTS nanocrystals as absorber layer.

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