Full Spectrum Utilization Research Articles

Carbon nanodots/WO3 nanorods Z-scheme composites: Remarkably enhanced photocatalytic performance under broad spectrum

The search for low-cost, earth-abundant and environmentally friendly photocatalysts that can efficiently function over the entire UV–vis–NIR spectrum remains one of the most pressing challenges in the photocatalytic elimination of pollutants from water. Herein, we accurately designed and fabricated a direct Z-scheme carbon nanodots/WO3 nanorods composite (CDots/WO3) with highly enhanced photo-response and broad-spectrum photocatalytic activity. Under ultraviolet, visible, near-infrared (UV, Vis, NIR) irradiation, respectively, the removal efficiencies of rhodamine B (RhB) always decreased in the order CDots/WO3 (97.1, 99.1, 61.2%)>prepared WO3 nanorods (66.6, 69.1, 22.4%)>commercial WO3 nanoparticles (22.1, 11.6, ∼0%). Additionally, reaction rate constants of 0.4030 and 0.2889h−1 were achieved by the CDots/WO3 nanocomposites when photo-oxidizing tetracycline hydrochloride (TCH) and phenol, respectively, both of which were ∼2.9 times higher than those for WO3 nanorods. This excellent photocatalytic performance was ascribed to synergistic effects, including the highly dispersed carbon nanodots on the surface of the WO3 nanorods and efficient charge separation induced by the heterostructure formed between carbon nanodots and WO3 nanorods. Accordingly, a mechanism was proposed to account for the photocatalytic reaction process. The prepared catalyst showed no obvious change in its photocatalytic performance or other chemical properties after 5 cycles of use. Therefore, the carbon nanodots/WO3 nanocomposites may represent a new strategy for the full-spectrum utilization of solar light, providing an invaluable methodology for the remediation of current water-pollution issues.

Experimental investigation on potential of a concentrated photovoltaic-thermoelectric system with phase change materials

Since the influence of temperature on the conversion efficiencies of photovoltaic (PV) cells and thermoelectric (TE) generators are totally different and opposite, the system operating temperature becomes a key parameter which significantly determines the utilization efficiency of the common PV-TE system on solar energy. In order to make the PV-TE system obtain higher energy utilization efficiency, phase change material (PCM) is incorporated to construct a novel PV-PCM-TE hybrid system to maintain the system operating at the ideal working temperature. The performance of such a novel hybrid system is experimentally studied corresponding to a number of practical working conditions. The temperature, efficiency, and output power of the hybrid system are compared with those of the pure PV system under the same circumstance. The effects of the optical concentrations ratio and cooling approaches on the conversion efficiency of the hybrid system are experimentally investigated. The whole conversion efficiencies of the hybrid system incorporated with TE generators with different values of dimensionless thermoelectric coefficient (ZT) are discussed. The present work reveals that such a hybrid system possesses a promising potential on the full-spectrum utilization of solar energy.

Spectral splitting optimization for high-efficiency solar photovoltaic and thermal power generation

Utilizing the full solar spectrum is desirable to enhance the conversion efficiency of a solar power generator. In practice, this can be achieved through spectral splitting between multiple converters in parallel. However, it is unclear which wavelength bands should be directed to each converter in order to maximize the efficiency. We developed a model of an ideal hybrid solar converter which utilizes both a single-junction photovoltaic cell and a thermal engine. We determined the limiting efficiencies of this hybrid strategy and the corresponding optimum spectral bandwidth directed to the photovoltaic cell. This optimum width is inversely proportional to the thermal engine efficiency and scales with the bandgap of the photovoltaic cell. This bandwidth was also obtained analytically through an entropy minimization scheme and matches well with our model. We show that the maximum efficiency of the system occurs when it minimizes the spectral entropy generation. This concept can be extended to capture generalized non-idealities to increase the usefulness of this technique for a range of full solar spectrum utilization technologies.

Full-spectrum photon management of solar cell structures for photovoltaic–thermoelectric hybrid systems

In this paper, a novel ultra-broadband photon management structure is proposed for crystalline silicon thin-film solar cells used in the photovoltaic–thermoelectric hybrid system. Nanostructures are employed on both front and back side. Optical behavior of the structure in ultra-broadband (300–2500nm) are investigated through the Finite Difference Time Domain method. By combing moth-eye and inverted-parabolic surface, a new composite surface structure is proposed for anti-reflection in the ultra-broadband wavelengths. Front metallic nanoparticles, plasmonic back reflector and metallic gratings are studied for light-trapping and the effect of plasmonic back reflector is validated by the experimental data of the external quantum efficiency. The effects of incident angle are discussed for metallic gratings. Numerical computation shows that the incorporation of anti-reflection and light-trapping can obtain high absorption in the solar cell and ensure the rest incident light transmits to the thermoelectric generator efficiently. This work shows potential full-spectrum utilization of solar energy for various photovoltaic devices related with hybrid photovoltaic–thermoelectric systems.

Enhanced photon harvesting in silicon multicrystalline solar cells by new lanthanide complexes as light concentrators

Four europium complexes with enhanced luminescent properties have been synthesized. Thin transparent films of the complexes were prepared on glass panes and then were examined as efficient luminescent solar concentrators for full spectrum utilization in crystalline silicon photovoltaic cells. The complexes could behave as efficient solar concentrators since they absorb UV light, where the spectral response of the crystalline silicon solar cells is low and they emit at 615 nm where the spectral response is maximum. The glass panes covered with europium complexes act as planar waveguides of the emitted light that is collected by the solar cells, which are attached to the edges of the solar concentrators. The europium complexes as solar concentrators were examined in terms of the optimum concentrations and the number of coatings, which were determined in order to evaluate the maximum performance of the solar cells. The case of multiple glass panes with europium complexes was also examined while a 28% maximum increase in the photocurrent was finally established.

Hybrid tandem solar cell for concurrently converting light and heat energy with utilization of full solar spectrum

A two-compartment hybrid tandem cell comprising a dye-sensitized solar cell as top cell and a thermoelectric cell as bottom cell has been developed to increase the overall photovoltaic conversion efficiency by utilization of full solar spectrum. The photovoltaic properties of the four-wire and two-wire hybrid tandem cells have been characterized and the working principle has been demonstrated using the electron energy band diagram. For two-wire hybrid tandem cells, the overall conversion efficiency can be improved by optimal designing DSC module in order to match the output current of the selected thermoelectric cell. Comparing with the individual dye-sensitized solar cell, an efficiency increase of 10% has been obtained for the hybrid tandem cell. The incident light intensity has no influence on the matching of the two compartments of the two-wire hybrid tandem cell.

Efficient conjugated polymer-ZnSe and -PbSe nanocrystals hybrid photovoltaic cells through full solar spectrum utilization

Type-II heterojunction poly[(2-methoxy,5-octoxy)-1,4-phenylenevinylene] (MOPPV)–ZnSe nanocomposites synthesized by in situ polymerization method are studied with and without incorporation of PbSe quantum dots (QDs) active layer in the novel hybrid photovoltaic device architecture for full solar spectrum utilization. The performance of the device improves significantly by incorporated PbSe QDs active layer. The power conversion efficiency, open-circuit voltage, short-circuit density and fill factor of the device with PbSe QDs are 0.14%, 0.806 V, 0.309 mA and 34%, respectively. It is expected that PbSe QDs active layer provides wider interface and surface areas for efficient exciton dissociation and charge transport, as well as more photon capture and exciton generation by absorption in near infrared spectrum region.

Molecular-based concepts in PV towards full spectrum utilization

Molecular-based concepts offer the potential of low materials and processing costs in photovoltaics (PV), which is especially interesting if high efficiencies can be obtained. To accomplish high efficiencies, a better utilization of the solar spectrum is of high importance. The concept of two-photon absorption in dye-sensitized solar cells and full spectrum aspects of luminescent flat plates concentrators are discussed in this paper. The two-photon dye cell can be compared to a tandem solar cell on the molecular level. The luminescent concentrator offers the potential to employ full spectrum utilization in combination with static concentration of both direct and diffuse light.