Full-spectrum Solar Energy Utilization Research Articles

Realization of omnidirectional ultra-broadband antireflection properties via subwavelength composite structures

An advanced subwavelength composite structure (SCS) consisting of the hexagonally arranged silicon nanopillars and the misaligned TiO2/SiO2 double-layer films was proposed on the surface of crystalline silicon (c-Si). After optimization through the finite difference time domain (FDTD) method, the SCS possesses omnidirectional ultra-broadband antireflection properties (average reflectance < 1.8% within 300–2500 nm) which are suitable for a photovoltaic-thermoelectric (PV-TE) hybrid system to enhance the full-spectrum solar energy utilization. Furthermore, the antireflection mechanism was studied in detail. The composition of nanopillars and double-layer films has combined the effect of interference, interpillar scattering and waveguide resonance to realize outstanding antireflection proprieties. The SCS was prepared on a 3 cm × 3 cm silicon wafer by ICP etching and magnetron sputtering, and the measured results matched well with the simulation results. Further, such antireflection concept can be applied to other materials for particular ultra-broadband spectrum regulation.

Broadband photon management of subwavelength structures surface for full-spectrum utilization of solar energy

In this work, advanced photon-management composite subwavelength structures are fabricated to manage solar energy in the full-spectrum (300–2500nm) wavelength range for the application of the photovoltaic-thermoelectric hybrid systems to fully utilize the solar energy. This proposed photon-management method will simultaneously realize efficient light trapping for the photons with above-bandgap energy in solar cells and the utilization of the below-bandgap photons and the waste heat resulting from the thermalization effect in solar cells with bottom thermoelectric devices. The typical structure is designed: Top ordered hexagonal nanohole arrays can trap above-bandgap photons to enhance the absorption in the silicon wafer, and TiO2/SiO2 bilayer films are deposited on the bottom side of the wafer to improve the transmission of the below-bandgap photons. ∼97% total absorptance for wavelengths of 300–1100nm is achieved with optimized diameters of central nanoholes. The total transmittance, on the other hand, is improved to ∼60% from 1200nm to 2500nm. The results indicate that the structures realize the appropriate allocation of photons within different wavelength ranges to different devices for sufficient utilization of full-spectrum solar energy. This novel full-spectrum photon management benefits from the strong scattering effect among the nanoholes and the gradient refractive index of bilayer films. Moreover, the photon-management performance shows angle-independent and polarization-insensitive characteristics. This method can be applied to various kinds of solar cells for photovoltaic-thermoelectric hybrid systems and may provide thoughts for other solar harvesting applications.

Full-spectrum light management by pseudo-disordered moth-eye structures for thin film solar cells.

In this paper, the role of pseudo-disordered moth-eye structures on the optical features for application to thin-film solar cells is investigated to realize the superior light management for the full-spectrum solar energy utilization, compared with some ordered structures. Without loss of generality, the c-Si thin film solar cell is taken as the example. The results demonstrate that the fluctuations introduced into the geometry parameters of moth-eye elements can lead to the remarkable absorption enhancement in the wavelength region of 0.3-1.1 μm and high transmission in the wavelength range of 1.1-2.5 μm. Two mechanisms including the increasing spectral density of modes and the intensive forescattering intensity are identified to be responsible for the absorption enhancement. In addition, the optical characteristics of the moth-eye surface with both disordered height and disordered diameter are insensitive to the incident angle.

Multi-scale investigation on the absorbed irradiance distribution of the nanostructured front surface of the concentrated PV-TE device by a MC-FDTD coupled method

Photovoltaic-thermoelectric (PV-TE) hybrid device is one of the most representative ways for the full-spectrum solar energy utilization. The concentrator and nanostructured front surface have become important approaches to improve the conversion efficiency of the PV-TE device by enhancing the solar energy absorption. However, the concentrator causes badly non-uniform absorbed irradiance distribution of the PV-TE device surface, which has a great influence on the conversion efficiency of the PV-TE device. In addition, due to the multi-scale problem, it is hard to study the combined effects of the concentrator and nanostructured surface on the absorbed irradiance distribution of the PV-TE hybrid device surface. In this paper, a 3D model for a concentrated PV-TE hybrid system that employs the PV-TE hybrid device with moth-eye nanostructures and a linear Fresnel reflective solar concentrator is established. For the multi-scale problem, a Monte Carlo-Finite Difference Time Domain (MC-FDTD) coupled method is presented. At first, three parameters including duty ratio, height, and diameter are used to analyze the influences of the moth-eye nanostructure dimension on the reflectance. Then, taking the effects of the sun shape, the slope error, and the polarization of incident electromagnetic wave into considerations, the comparison and analysis on the absorbed irradiance distributions of PV-TE surface under four different conditions (with plane surface, with nanostructured front surface, with concentrator and plane surface, with concentrator and nanostructured front surface) were conducted by the MC-FDTD coupled method. Eventually, based on the precious investigation, a novel way of using different dimensional nanostructures is proposed to improve the uniformity of the absorbed irradiance distribution. As a result, this approach not only improve the uniformity of absorbed irradiance distribution very well, but also can let the mean absorbed irradiance be raised 1.6 times to reach 7644.14W/m2 compared to plane surface.

Multi-scale Investigation on the Optical Performance of a Concentrated Photovoltaic Thermoelectric Hybrid System by a MC-FDTD Coupled Method

Abstract Taking photovoltaic-thermoelectric (PV-TE) hybrid system with the full-spectrum solar energy utilization as application background, a 3D model for a PV-TE hybrid system that employs nanostructure surface and a linear Fresnel reflective solar concentrator was developed in this paper. In this model, a Monte Carlo-Finite Difference Time Domain (MC-FDTD) coupled method is presented to solve the multiscale optical problems. On the premise of taking the effects of the sun shape, the slope error and the polarization of incident electromagnetic wave into consideration, the combined effects of the concentrator and nanostructure surface on the absorbed irradiance distribution of the hybrid system surface were studied. Three parameters of the dimensions for the moth-eye nanostructure, including duty ratio, height and diameter, are optimized, and the optimized duty ratio is 100%, the height is 0.9 μm and the diameter is 0.3 μm. The absorbed irradiance of the moth-eye surface with concentrator is increased at least fourteen-fold compared to plane surface without concentrator. The results from present work can offer a reference for the study supplies theory, means and data bases for the optimization of the nanostructure surface, homogenization of the absorbed irradiance distribution and efficient utilization of the solar energy.

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.

From light trapping to solar energy utilization: A novel photovoltaic–thermoelectric hybrid system to fully utilize solar spectrum

In this paper, the comprehensive photon and thermal management approaches are proposed to increase the full-spectrum solar energy utilization in PV–TE (photovoltaic–thermoelectric) hybrid systems. The bio-inspired moth-eye nanostructured surface is adopted to suppress the reflection for full solar spectrum photons while the enhanced transmission film is used to improve the transmission for photons with energy below the band-gap of PV cells, making the reasonable utilization of solar spectrum energy. The PV–TE hybrid system is studied for both terrestrial and space applications, corresponding to different thermal management approaches. The effects of geometric parameters, incident angle, thermal concentration ratio, and optical concentration ratio on the system performance are discussed. The results show that the PV–TE hybrid system exhibits better performance under both AM1.5 and AM0 illumination without any optical concentration compared to pure PV cells under the same conditions. For an optical concentrated solar PV–TE system, although the efficiency of the system may decrease with the increment of optical concentration ratio, the total power output increases for both terrestrial and space applications. The results indicate that a lower concentration ratio is more suitable for PV–TE hybrid systems in both terrestrial and space applications unless more powerful temperature management tricks are taken.

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.