Minmin Han

Fabrication and photoelectrochemical characteristics of CuInS2 and PbS quantum dot co-sensitized TiO2 nanorod photoelectrodes

A cascade structured PbS/CuInS2/TiO2 photoelectrode with a co-sensitizer of CuInS2 and PbS quantum dots (QDs) deposited on TiO2 nanorods is fabricated via a successive ionic layer absorption and reaction (SILAR) method. The effects of SILAR cycle numbers of n and m for CuInS2 QDs and PbS QDs, as well as the influence of the co-sensitization of QDs on the energy conversion efficiency, are discussed. The results show that the deposition of co-sensitizer PbS QDs on CuInS2 QDs–TiO2 nanorod array photoelectrodes presents a complementary effect in light absorption. The performance of quantum dot sensitized solar cells (QDSSCs) shows dominant dependence on the value of SILAR cycles n and m. The enhanced performance of QDSSCs with the cascade structure, PbS/CuInS2/TiO2 photoelectrode, is attributed to the Fermi energy level alignment of the QDs co-sensitizer. An energy conversion efficiency of 4.11% is achieved using the PbS/CuInS2/TiO2 photoelectrodes under one sun illumination (AM 1.5, 100 mW cm−2).

Photoelectrochemical properties of PbS quantum dot sensitized TiO2 nanorods photoelectrodes

The semiconductor PbS quantum dots (QDs) were synthesized on TiO2 nanorods (NRs) via a successive ionic layer adsorption and reaction (SILAR) method. The deposition of PbS QDs on the TiO2 NRs could enhance the ability of light absorption and improve the power conversion efficiency of the solar cell. The morphological features, crystal structures, optical properties, photoelectrochemical performances, electron transfer at the TiO2-QDs/electrolyte interface and electron lifetime of the obtained PbS QDs/TiO2 NRs photoelectrodes were characterized and discussed in detail. The results demonstrated that the photoelectrochemical performance of PbS QDs/TiO2 NRs depends on the value of the SILAR cycle number. The highest photoelectric conversion efficiency of 0.77% is achieved at the SILAR cycle number n = 4 under one sun illumination (AM 1.5, 100 mW cm−2). The enlarged absorption edges to the visible region and the effective separation of photogenerated electron–hole pairs at the PbS QDs-TiO2 NRs interface are attributed to the promotion of the power conversion efficiency.

3D Bi2S3 salix leaf-like nanosheet/TiO2 nanorod branched heterostructure arrays for improving photoelectrochemical properties

We firstly fabricated a peculiar 3D structure of Bi2S3 salix leaf-like nanosheet/TiO2 nanorod branched heterostructure arrays by a convenient hydrothermal method and discussed their mechanism of improving photoelectrochemical cell (PEC) properties. The salix leaf-like Bi2S3 nanosheets (NSs) were grown on TiO2 nanorod arrays through controlling the molar ratio of EDTA-Na2/Bi3+ and the reaction time. The morphology, crystal structure, microstructure and optical performance of the 3D Bi2S3 NS/TiO2 NRs at different reaction times were investigated. The results show that the branched heterostructure of 3D Bi2S3 NS/TiO2 NR arrays exhibits enhanced photocurrent density and optical absorption, which were attributed to the larger Bi2S3 surface area, as well as a direct electron path within the salix leaf-like Bi2S3 NS and TiO2 NR heterojunctions, resulting from more excitation sites of incident light. The photocurrent density of the 3D Bi2S3 NS/TiO2 NR arrays was almost 9 times greater than that of pristine TiO2 without a branching structure. The results of the present work demonstrate that fabrication of the branched Bi2S3 NS/TiO2 NR heterogeneous structure is a significant fabrication technology with great promise in PECs.

Sn doping induced intermediate band in CuGaS2

Sn doped CuGaS2 has been investigated as an intermediate band (IB) material. Our results indicate that Sn doping can indeed induce IBs in the band gap of CuGaS2 and the optical absorption and solar energy utilization are greatly enhanced due to the existence of the IBs. Though all Sn doped structures concerned are dynamically stable, we found that under thermal equilibrium growth conditions, the CuGaS2 should be moderately doped to maintain its stability over a chemical potential region in order to achieve novel optoelectronic IB materials growth.

Pulsed laser deposition of a Bi2S3/CuInS2/TiO2 cascade structure for high photoelectrochemical performance

The PLD technique is used for the direct fabrication of QD sensitized solar cells (QDSSCs) without any encapsulation and/or resorting to any surface treatment, ligand engineering and/or post-synthesis processing which might involve some toxic chemical regents harmful to the performance of solar cells. In this paper, co-sensitizers of Bi2S3 and CuInS2 quantum dots (QDs) are deposited on TiO2 nanorods via a physical deposition-based pulsed laser deposition (PLD) technique to fabricate the cascade structure of Bi2S3/CuInS2/TiO2. The performance of the QDSSCs with a cascade structure is optimized by adjusting the laser energy, and an energy conversion efficiency of 4.81% is achieved under one sun illumination (AM 1.5, 100 mW cm−2). Besides, the photovoltaic device exhibits high stability in air without any specific encapsulation. The improved performance is attributed to enhanced absorption in the longer wavelength region, quicker interfacial charge transfer and less chance of electron recombination with holes. Moreover, the direct atomic contact by the PLD technique and the cascade structure are also favorable factors for the enhanced photoelectrochemical performance of QDSSCs.

Controllable coverage of Bi2S3 quantum dots on one-dimensional TiO2 nanorod arrays by pulsed laser deposition technique for high photoelectrochemical properties

In this work, the pulsed laser deposition (PLD) technique is applied for direct physical deposition of narrow bandgap semiconductor Bi2S3 quantum dots (QDs) on one-dimensional TiO2 nanorod arrays to fabricate quantum dots sensitized solar cells (QDSSCs). Without regard for any protective packaging or surface treatment process for binding QDs, the QDSSCs exhibit excellent stability and high energy conversion efficiency in ambient air. Through varying the laser ablation pulses, the controlled coverage of QDs on nanorods is realized and an optimal energy conversion efficiency of 3.06% is obtained under one sun illumination (AM 1.5, 100 mW cm−2). The enhanced absorption in an extended wavelength range, quick interfacial charge transfer and few recombination chances for electrons with holes are believed to contribute to the improved performance of Bi2S3 QD-sensitized solar cells. Moreover, a sputtered plasma at high velocity can collide intensely with the surface of TiO2, which enables direct atomic contact and endows the QDSSCs with high stability. These promising results provide a potential option of using the PLD technique for the fabrication of QD-based solar cells or other thin film photo-absorption materials.