Spectrum-splitting System Research Articles

Spectral Splitting Solar Cells Consisting of a Mesoscopic Wide-Bandgap Perovskite Solar Cell and an Inverted Narrow-Bandgap Perovskite Solar Cell.

In comparison to monolithic perovskite/perovskite double-junction solar cells, a four-terminal spectrum-splitting system is a simple method to obtain a higher power conversion efficiency (PCE) because it has no constraints of unifying the structures of the top and bottom cells. In this work, utilizing the fact that low-bandgap Sn-Pb bottom cells work the best in p-i-n while Pb-based wide-bandgap top cells work better in an n-i-p architecture, a wide-bandgap (Eg = 1.61 eV) perovskite solar cell with a mesoscopic structure and a narrow-bandgap (Eg = 1.27 eV) perovskite solar cell with an inverted structure were combined to fabricate a double-junction four-terminal spectral splitting solar cell. The double-junction solar cell with the 801 nm spectral splitting with an active area of 0.18 cm2 was found to work with a PCE of 25.3%, which is the highest reported so far for a 4-T all-perovskite double-junction spectral splitting solar cell.

Experimental study of a concentrating solar spectrum splitting system for hybrid solar energy conversion

Spectral beam-splitting represents a potential approach to enhance energy conversion in solar concentrating systems. This study introduces a novel hybrid solar concentrator system, comprising a dish reflector with a two-axis tracking system and an affordable optical linear system that divides the concentrated solar beam into distinct visible spectral bands. Experimental investigations were conducted, encompassing an optical analysis of the splitter system and an assessment of photovoltaic and thermal power generation from the prototype throughout a day with solar tracking. Results indicate that the splitter system achieved a transmissivity of 76 % within the 400–800 nm range with clear separation between spectral bands, demonstrating system reliability. Spectral band dimensions remained relatively constant throughout the day, with widths of 0.460 cm, 0.550 cm, and 0.700 cm for red, blue, and yellow bands, respectively. The photovoltaic cell exposed to the yellow band exhibited the highest power and current intensities, with power densities of 15 mW/cm2 at noon, compared to 12 mW/cm2 for the blue and 5 mW/cm2 for the red bands. The system also recovered thermal power, reaching a maximum of 190 W around noon. The paper discusses suitable photovoltaic cell types for each band color and explores opportunities for improved efficiency and large-scale implementation.

A Comparison of Spectrum-Splitting Configurations for High-Efficiency Photovoltaic Systems With Perovskite Cells

The recent development of inexpensive perovskite photovoltaic (PV) cells at a variety of band gap energies has opened the prospects for commercially viable spectrum-splitting PV systems. A variety of cell configurations exist for implementing spectrum splitting in PV modules. In this article, 3-junction and 4-junction hybrid spectrum-splitting systems are proposed that use volume holographic lens arrays for lateral spectral separation and absorptive filtering in semitransparent perovskite PV cells for vertical spectral separation. A 3-junction hybrid system is shown to have greater conversion efficiency (28.7%) than comparable systems using completely lateral (25.6%) or completely stacked (26.9%) cell arrangements. It is shown that a 4-junction hybrid system has a hypothetical conversion efficiency of 30.0% using perovskite PV cells that have been experimentally demonstrated in the literature with energy band gaps of 1.25 eV, 1.55 eV, 1.72 eV, and 2.30 eV.

Lateral spectrum splitting system with perovskite photovoltaic cells

We examine the potential of a multijunction spectrum-splitting photovoltaic (PV) solar energy system with perovskite PV cells. Spectrum splitting allows combinations of different energy band gap PV cells that are laterally separated and avoids the complications of fabricating tandem stack architectures. Volume holographic optical elements have been shown to be effective for the spectrum-splitting operation and can be incorporated into compact module packages. However, one of the remaining issues for spectrum splitting systems is the availability of low-cost wide band gap and intermediate band gap cells that are required for realizing high overall conversion efficiency. Perovskite PV cells have been fabricated with a wide range of band gap energies that potentially satisfy the requirements for multijunction spectrum-splitting systems. A spectrum-splitting system is evaluated for a combination of perovskite PV cells with energy band gaps of 2.30, 1.63, and 1.25 eV and with conversion efficiencies of 10.4%, 21.6%, and 20.4%, respectively, which have been demonstrated experimentally in the literature. First, the design of a cascaded volume holographic lens for spectral separation in three spectral bands is presented. Second, a rigorous coupled wave model is developed for computing the diffraction efficiency of a cascaded hologram. The model accounts for cross-coupling between higher diffraction orders in the upper and lower holograms, which previous models have not accounted for but is included here with the experimental verification. Lastly, the optical losses in the system are analyzed and the hypothetical power conversion efficiency is calculated to be 26.7%.

Perovskite/CIGS Spectral Splitting Double Junction Solar Cell with 28% Power Conversion Efficiency.

SummaryThe highest theoretical efficiency of double junction solar cells is predicted for architectures with the bottom cell bandgap (Eg) of approximately 0.9–1.0 eV, which is lower than that of a typical Si cell (1.1 eV). Cu(In,Ga)(Se,S)2 (CIGS) solar cells exhibit a tunable Eg depending on their elemental composition and depth profile. In this study, various CIGS solar cells with Eg ranging from 1.02 to 1.14 eV are prepared and a spectrum splitting system is used to experimentally demonstrate the effect of using lower-Eg cells as the bottom cell of two-junction solar cells. The four-terminal tandem cell configuration fabricated using a mixed-halide perovskite top cell (Eg = 1.59 eV; stand-alone efficiency = 21.0%) and CIGS bottom cell (Eg = 1.02 eV; stand-alone efficiency = 21.5%) with a 775-nm spectral splitting mirror exhibits an efficiency of 28.0% at the aperture area of 1 cm2.

Dispersive Optical Systems for Highly-Concentrated Solar Spectrum Splitting: Concept, Design, and Performance Analyses

We present a concept design of a solar spectrum splitting system that enables highly-concentrated solar energy harvesting over the entire AM1.5 spectral range. After passing through an array of the dispersive optical system (DOS) module composed of a grating structure and dispersive prisms below a concentrating lens, incident sunlight can be separated into two wavelength bands of visible (VIS) and infrared (IR) ranges, which can then be focused onto corresponding solar receivers. Based on the spectral response of typical crystalline silicon solar cells, the VIS wavelength band is selected from 0.4 μm to 1.2 μm to contribute to photovoltaic (PV) conversion to generate electricity. Meanwhile, the IR band in longer wavelength ranges (1.2 μm ≤ λ ≤ 2.5 μm), which does not contribute to PV conversion, can be simultaneously used for solar thermal applications such as water heating and thermoelectricity. In this paper, various design parameters (e.g., focal length of a concentrating lens, groove density of a grating, geometry of dispersive prisms, material combination of optical components, etc.) have been investigated to determine an optimum set of system configurations, using optical design software (Zemax OpticStudio 14.2). Our simulation studies validate that the DOS is able to split incident AM1.5 solar irradiance into the two wavelength bands of the VIS and IR ranges and focus each wavelength band with concentration factors as high as 798× and 755× on the same focal plane, respectively. Such high concentration factors for both wavelength bands can be actualized due to the additional optical components used—a grating structure and dispersive prisms, which allow to minimize optical aberrations through both diffraction and refraction. The proposed DOS, designed with commercially available optical components, has the potential to widen the use of the sun’s spectrum by allowing effective PV conversion of solar cells under high concentration with tolerable optical system losses and concurrently converting the remaining solar irradiation into useful energy for a broad range of thermal applications.

Optimization and maximum efficiency of concentrating photovoltaic cell‐gas turbine system with spectrum splitting

AbstractThe spectrum splitting system (SSS) is an efficient approach to relieve the energy losses in the solar cell and boost the efficiency of solar energy utilization. A model of the concentrated solar spectrum splitting photovoltaic (PV) cell‐gas turbine (GT) hybrid system is established to evaluate the performance of the system and predict the maximum efficiency. The numerical calculations show that the area ratio of the solar collector to the PV cell significantly affects the maximum efficiency of the spectrum system, but most of the previous studies are not considered. The maximum efficiency of the system is 50.6% when the parameters including the cell voltage, collector temperature, and band gap energy of the PV cell are optimized at the same areas of the collector and PV cell. The proposed SSS can achieve the maximum efficiency of 52.3% when the area ratio of the collector to the PV cell is further optimized. The results obtained are compared with those of a single concentrating PV cell or solar‐powered GT, and consequently, the advantages of a concentrating spectrum splitting PV cell‐GT hybrid system are revealed.

Research on the novel explicit model for photovoltaic I-V characteristic of the single diode model under different splitting spectrum

Abstract Photovoltaic (PV) panel has been widely used in many spectrum splitting systems. However the spectrum splitting normally discussed only with photocurrent. In this paper, the relationship between the current-voltage (I-V) curve and the irradiation spectrum is discussed by combining the single diode model. An explicit elementary analytical model with two defined shape parameters is improved with three approximations and second order Taylor expansion. The relationship between the physical parameters and the condition parameters is applied to extract the shape parameters at different scenarios. Considering the aging effect, the process of calculation to predict I-V curve is simplified as follow: (1) two shape parameters are gotten from I-V data at measurement reference conditions (MRC); (2) short circuit current, open circuit voltage and shape parameters under any splitting spectrum can be calculated based on the relationship provided in article; (3) the performance of PV panel can be predicted with parameters. The validation of this model was experimentally proven leveraging monocrystalline silicon photovoltaic module with different splitting films. Moreover, the presented model performs superior compared to other investigated models when looking at accuracy and simplicity.

Maximum efficiency and parametric optimum selection of a concentrated solar spectrum splitting photovoltaic cell-thermoelectric generator system

An updated model of the solar spectrum splitting photovoltaic cell-thermoelectric generator system is used to derive the analytical expression of the systemic efficiency. The cutoff energy of the system, cell voltage, and dimensionless current of the thermoelectric generator are optimized. Particularly, the influences of the area ratio of the collector to photovoltaic cell on the performance of the spectrum splitting system are discussed in detail. The maximum efficiencies of the spectrum splitting system are calculated for given solar concentration factors. The results obtained are compared with those of the single photovoltaic cell with the same solar concentration factor. It is found that the maximum efficiency of the system can be further improved when the area ratio is optimized. The expressions of the upper and lower bounds of the optimized area ratio are derived. The spectrum splitting system can more efficiently harvest the full solar spectrum than the single photovoltaic cell, especially at low solar concentration factors. For example, when solar concentration factors are, respectively, equal to 30 and 100, the maximum efficiencies of the spectrum splitting system attain 39.5% and 40.2% and increase approximately 2.67% and 2.19%, compared to those of the single photovoltaic cell.

Broadband perfect light trapping in the thinnest monolayer graphene-MoS2 photovoltaic cell: the new application of spectrum-splitting structure.

The light absorption of a monolayer graphene-molybdenum disulfide photovoltaic (GM-PV) cell in a wedge-shaped microcavity with a spectrum-splitting structure is investigated theoretically. The GM-PV cell, which is three times thinner than the traditional photovoltaic cell, exhibits up to 98% light absorptance in a wide wavelength range. This rate exceeds the fundamental limit of nanophotonic light trapping in solar cells. The effects of defect layer thickness, GM-PV cell position in the microcavity, incident angle, and lens aberration on the light absorptance of the GM-PV cell are explored. Despite these effects, the GM-PV cell can still achieve at least 90% light absorptance with the current technology. Our proposal provides different methods to design light-trapping structures and apply spectrum-splitting systems.

Four-Terminal Tandem Solar Cells Using CH3NH3PbBr3 by Spectrum Splitting.

In this work, the use of a high bandgap perovskite solar cell in a spectrum splitting system is demonstrated. A remarkable energy conversion efficiency of 23.4% is achieved when a CH3NH3PbBr3 solar cell is coupled with a 22.7% efficient silicon passivated emitter rear locally diffused solar cell. Relative enhancements of >10% are demonstrated by CH3NH3PbBr3/CH3NH3PbI3 and CH3NH3PbBr3/multicrystalline-screen-printed-Si spectral splitting systems with tandem efficiencies of 13.4% and 18.8%, respectively. The former is the first demonstration of an all perovskite split spectrum system. The CH3NH3PbBr3 cell on a mesoporous structure was fabricated by the vapor-assisted method while the planar CH3NH3PbI3 cell was fabricated by the gas-assisted method. This work demonstrates the advantage of the higher voltage output from the high bandgap CH3NH3PbBr3 cell and its suitability in a tandem system.

Optical performance of dichroic spectrum-splitting filters

We investigate the optical performance of dichroic filters used in solar spectrum-splitting applications. Photovoltaic (PV) systems utilizing spectrum splitting have higher theoretical conversion efficiency than single-bandgap PV modules. Dichroic filters have been used in several spectrum-splitting optical system designs with success. However, dichroic filters only achieve ideal performance under collimated incident light. With an incident angle constraint the optical concentration ratio is limited. A high-concentration ratio helps to achieve high-conversion efficiency and control cost by reducing the PV cell area. In a dual-junction spectrum-splitting PV configuration with a gallium arsenide (GaAs) PV cell and a 2.1-eV bandgap PV cell, the experimental dichroic filter can provide 86.3% of the ideal designed performance. The filter nonideal performance under focused incident light is simulated with ZEMAX. System efficiency under different F-number and filter refractive index is simulated for dual-junction and three-junction systems to show the performance of dichroic filters. We have found that for a dual-bandgap spectrum-splitting system there is a 0.32% system efficiency gain associated with a filter refractive index increased from 1.5 to 1.95. An efficiency gain of 0.41% is associated with an aperture size reduction from F2.0 to F3.0. In a three-junction configuration, simulation shows that a 0.57% system efficiency gain is possible when the filter refractive index is increased from 1.5 to 1.95. An efficiency gain of 0.63% is associated with an aperture size reduction from F2.0 to F3.0.

Spectrum splitting metrics and effect of filter characteristics on photovoltaic system performance.

During the past few years there has been a significant interest in spectrum splitting systems to increase the overall efficiency of photovoltaic solar energy systems. However, methods for comparing the performance of spectrum splitting systems and the effects of optical spectral filter design on system performance are not well developed. This paper addresses these two areas. The system conversion efficiency is examined in detail and the role of optical spectral filters with respect to the efficiency is developed. A new metric termed the Improvement over Best Bandgap is defined which expresses the efficiency gain of the spectrum splitting system with respect to a similar system that contains the highest constituent single bandgap photovoltaic cell. This parameter indicates the benefit of using the more complex spectrum splitting system with respect to a single bandgap photovoltaic system. Metrics are also provided to assess the performance of experimental spectral filters in different spectrum splitting configurations. The paper concludes by using the methodology to evaluate spectrum splitting systems with different filter configurations and indicates the overall efficiency improvement that is possible with ideal and experimental designs.

GaP, AlGaAs/GaAs, AlGaAsSb/GaSb Photovoltaic Devices and Characteristics

Solar cells using GaP, AlGaAs/GaAs, and AlGaAsSb/GaSb p-n junctions for a spectrum-splitting system have been studied to obtain a high conversion efficiency and a high output power. The GaP solar cell with Si3N4 anti-reflection coating exhibited the conversion efficiency η of 7.6% by the spectrum-splitting (0.35 µm<λ<0.50 µm), while η of AlGaAsSb/GaSb solar cell with a window layer of Al0.34Ga0.66As0.013Sb0.987 quaternary alloy was 1.84% even by spectrum-splitting (1.15 µm<λ<1.65 µm). The low conversion efficiency of the AlGaAsSb/GaSb solar cell is due partly to surface leakage current.