The emergence of semiconductor nanocrystals as the building blocks of nanotechnology has opened up new ways to utilize them in next generation solar cells. This paper focuses on the recent developments in the utilization of semiconductor quantum dots for light energy conversion. Three major ways to utilize semiconductor dots in solar cell include (i) metal−semiconductor or Schottky junction photovoltaic cell (ii) polymer−semiconductor hybrid solar cell, and (iii) quantum dot sensitized solar cell. Modulation of band energies through size control offers new ways to control photoresponse and photoconversion efficiency of the solar cell. Various strategies to maximize photoinduced charge separation and electron transfer processes for improving the overall efficiency of light energy conversion are discussed. Capture and transport of charge carriers within the semiconductor nanocrystal network to achieve efficient charge separation at the electrode surface remains a major challenge. Directing the future resear...

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Quantum Dot Solar Cells. Semiconductor Nanocrystals as Light Harvesters

In the last three decades, zero-dimensional, one-dimensional, and two-dimensional carbon nanomaterials (i.e., fullerenes, carbon nanotubes, and graphene, respectively) have attracted significant attention from the scientific community due to their unique electronic, optical, thermal, mechanical, and chemical properties. While early work showed that these properties could enable high performance in selected applications, issues surrounding structural inhomogeneity and imprecise assembly have impeded robust and reliable implementation of carbon nanomaterials in widespread technologies. However, with recent advances in synthesis, sorting, and assembly techniques, carbon nanomaterials are experiencing renewed interest as the basis of numerous scalable technologies. Here, we present an extensive review of carbon nanomaterials in electronic, optoelectronic, photovoltaic, and sensing devices with a particular focus on the latest examples based on the highest purity samples. Specific attention is devoted to each class of carbon nanomaterial, thereby allowing comparative analysis of the suitability of fullerenes, carbon nanotubes, and graphene for each application area. In this manner, this article will provide guidance to future application developers and also articulate the remaining research challenges confronting this field.

Carbon nanomaterials for electronics, optoelectronics, photovoltaics, and sensing

TiO2 nanotube arrays and particulate films are modified with CdS quantum dots with an aim to tune the response of the photoelectrochemical cell in the visible region. The method of successive ionic layer adsorption and reaction facilitates size control of CdS quantum dots. These CdS nanocrystals, upon excitation with visible light, inject electrons into the TiO2 nanotubes and particles and thus enable their use as photosensitive electrodes. Maximum incident photon to charge carrier efficiency (IPCE) values of 55% and 26% are observed for CdS sensitized TiO2 nanotube and nanoparticulate architectures respectively. The nearly doubling of IPCE observed with the TiO2 nanotube architecture is attributed to the increased efficiency of charge separation and transport of electrons.

Photosensitization of TiO2 Nanostructures with CdS Quantum Dots: Particulate versus Tubular Support Architectures

3.1. Fundamental Characterization 6672 3.2. Photocurrent Action Spectroscopy 6673 3.3. Optical Characterization 6673 3.4. Characterization of Electron Transfer 6673 4. Electron Transport in Metal Oxide Films 6674 4.1. Mechanism of Photoinduced Carrier Transport 6674 4.2. Characterization of Diffusion Length 6675 4.3. One-Dimensional (1-D) Transport Architectures 6675 4.4. Electrolyte Interactions 6676 5. Recent Trends in Liquid-Junction Solar Cells 6676 5.1. Dye Sensitized Solar Cells 6677 5.2. Quantum Dot Sensitized Solar Cells 6678 5.3. Carbon Nanostructure Based Photochemical Solar Cells 6679

Beyond Photovoltaics: Semiconductor Nanoarchitectures for Liquid-Junction Solar Cells

Multi-walled carbon nanotubes (MWNT) and TiO2 composite catalysts were prepared by a modified sol–gel method. The nanoscaled composite materials were extensively characterized by TG, N2 adsorption-desorption isotherm, XRD, SEM, EDX, TEM and UV–vis spectra. The photocatalytic degradation of phenol was performed under visible light irradiation on these catalysts. An optimum of synergetic effect on photocatalytic activity was observed for a weight ratio MWNT/TiO2 equal to 20% with an increase in the first-order rate constant by a factor of 4.1. The synergetic effect, induced by a strong interphase interaction between MWNT and TiO2, was discussed in terms of different roles played by MWNT in the composite catalysts.

Visible light photodegradation of phenol on MWNT-TiO2 composite catalysts prepared by a modified sol–gel method

The effect of incorporating single-wall carbon nanotubes in TiO2 film electrodes on the properties of dye-sensitized solar cells was studied. Compared with an unmodified solar cell, it is observed that the short-circuit photocurrent (Jsc) of the modified solar cells increases while the open-circuit photovoltage decreases slightly. The enhanced Jsc is correlated with increased electrical conductivity, light scattering and concentration of free conduction band electrons.

Enhanced Photocurrent of Dye-Sensitized Solar Cells by Modification of TiO2 with Carbon Nanotubes.

The effects of using indium zinc oxide (IZO) as a conducting substrate in dye-sensitized TiO2 solar cells (DSC) on their photocurrent−voltage characteristics are studied. We have found that both short-circuit photocurrent (Jsc) and open-circuit voltage (Voc) of IZO-based cells are substantially improved by about 40% and 10%, respectively, when compared with those of cells based on fluoride-doped tin oxide (FTO). The Jsc increase is correlated to the improved contact between IZO and TiO2 and enriched conduction band electrons in the TiO2-on-IZO electrode, due to the blocking of surface states by the evaporated metallic components of the substrate. The combined effects of the negative shift of flat band potential and the reduction in recombination explain the Voc increase. Our experimental finding suggests that IZO-coated substrate makes more efficient DSC than a FTO-coated one.

Enhancement of Photocurrent and Photovoltage of Dye-Sensitized Solar Cells with TiO2 Film Deposited on Indium Zinc Oxide Substrate

The photodegradation reaction rate of 4-chlorophenol (4-CP) with a titanium silicalite–2 (TS-2) catalyst is found to be faster in the initial stage than with TiO2. This is primarily due to the stronger adsorption of 4-CP on the hydrophobic surface of the TS-2 catalyst. The hydrophobicity is evaluated by determining the distribution coefficients (D) between TS-2 and aqueous medium using a variety of aromatic hydrocarbons. The larger the D, the faster the initial reaction rate. The D correlates with solubility in water and partition coefficient, log Poct.

Jin Sup Hong

Papers

Enhanced Photocurrent of Dye-Sensitized Solar Cells by Modification of TiO2 with Carbon Nanotubes.

Enhancement of Photocurrent and Photovoltage of Dye-Sensitized Solar Cells with TiO2 Film Deposited on Indium Zinc Oxide Substrate

Photodecomposition of 4-Chlorophenol Catalyzed by Titanium Silicalite-2