In the last decade, there has been great interest in Lead Sulfide (PbS) quantum dots because of its potential application in multiple exciton generation solar cell. In order to fabricate the solar cell, it is necessary to synthesize PbS nanocrystals in the size less than 18 nm [1] on appropriate substrates. Chemical bath deposition (CBD) is one of the most popular solution-based processes for synthesis of PbS crystals on substrates. However, the typical size of CBD-synthesized PbS crystals is rather large, 0.1–1.0 μm　in diameter [2]. Recently, Osherov et al. pointed out the possibility that the crystal size and shape could be controlled by varying the deposition conditions, such as reagents concentrations or temperature [3]. Nevertheless, to our knowledge, no successful synthesis of PbS quantum dots on substrates by CBD has been reported so far. In the present work, we have systematically studied the effect of reagents concentrations on the size of chemically deposited PbS crystals.

CBD experiments were performed on indium tin oxide coated glass substrates with basically the same method as described by Osherov et al. [3]. Atomic Force Microscopy showed that the dark brown films deposited on the substrates were composed of numerous polyhedral-shaped small particles. It was found that the particle size was strongly affected by CS(NH₂)₂ concentration: Increase of the concentration from 0.036 to 0.720 M lead to monotonous decrease of the particle size from 200 to 50 nm, while the density of the particles were increased. Moreover, X-ray diffraction spectra of the samples revealed that the deposited particles were face-centered-cubic rock-salt structured PbS, irrespective of concentration of CS(NH₂)₂. Taking into account the given equilibrium reagents concentrations, it is most likely that the change of the crystal size is due to the change of supersaturation in deposition solution. In this regard, we will also discuss the effect of NaOH and Pb(CH₃COO)₂ concentrations on the PbS crystal size in detail.

References

[1] A. K. Dutta, et al., Journal of Chemical Materials, 12 (2000) 1042.

[2] Z. Zhao, et al., Journal of Colloids and Surfaces A, 355 (2010) 114.

[3] A. Osherov, et al., Journal of Physical State Solid C 5, 11 (2008) 3431.

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