Spectrum splitting photovoltaics: Materials and device parameters to achieve ultrahigh system efficiency

Warmann, Emily C.; Eisler, Carissa N.; Kosten, Emily D.; Escarra, Matthew D.; Atwater, Harry A.

doi:10.1109/pvsc.2013.6744845

Cited by 8 publications

(8 citation statements)

References 10 publications

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“…Once optical losses and realistic cell performance are included, six junctions are simply not enough to reach 50% efficiency. 7 While in previous work we considered four underlying dual junctions, we achieved optical efficiencies somewhat lower than desirable with realistic filters.…”

Section: Summary Of Resultsmentioning

confidence: 91%

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Spectrum splitting photovoltaics: Light trapping filtered concentrator for ultrahigh photovoltaic efficiency

Kosten

Lloyd

Warmann

et al. 2013

2013 IEEE 39th Photovoltaic Specialists Conference (PVSC)

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While monolithic multijunction solar cell approaches have been quite successful, current and lattice matching requirements limit the maximum possible achievable efficiencies. Spectrum splitting, where light is optically distributed among subcells with differing bandgaps, avoids these constraints and offers a route to achieving higher efficiencies (>50%). We investigate a spectrum splitting approach where concentrated sunlight is trapped in a textured dielectric slab and then selectively coupled into underlying solar cells of different bandgaps through omnidirectional filters. We develop a multipass optical model to find regimes of high optical efficiency based on parameters such as slab refractive index, number of subcells, and angle restriction of light escape from the slab. Based on these results and filter design considerations, we describe a specific design featuring a textured slab of SiO 2 coated with angle restricting incoupling elements based on compound parabolic concentrators and three underlying multijunction junction solar cells, for a total of eight junctions with bandgaps ranging from 2.2eV to 0.7. Using the multipass model in conjunction with modified detailed balance calculations, we find module efficiencies exceeding 50% are possible with an acceptance angle restricted to 20° or less and concentrations of a few hundred suns with ideal omnidirectional filters. Finally as proof of concept, we design a full set of omnidirectional filters for this design. Based on alternating layers of TiO 2 and SiO 2 , we achieve angle averaged reflectivity greater than 90% within the reflection band and angle averaged transmission of approximately 90% within the transmission band for the long pass filter, for nearly 48% receiver efficiency.

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Section: Summary Of Resultsmentioning

confidence: 91%

“…These optimizations assume a 1% external radiative efficiency (ERE), 90% of ideal current, and 500x concentration. 7,8 However, the top bandgap was very high, such that it would be difficult to fabricate with high ERE. Therefore, we limited the top bandgap to 2.2 eV and re-optimized.…”

Section: Summary Of Resultsmentioning

confidence: 99%

Spectrum splitting photovoltaics: Light trapping filtered concentrator for ultrahigh photovoltaic efficiency

Kosten

Lloyd

Warmann

et al. 2013

2013 IEEE 39th Photovoltaic Specialists Conference (PVSC)

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“…This design includes seven subcells ( Figure 1a) that were optimized using modified detailed balance calculations. 5 The quality of the subcells is determined by two parameters. The external radiative efficiency (ERE) of the subcells accounts for nonradiative recombination in the subcells and primarily affects the voltage.…”

Section: Summary Of Resultsmentioning

confidence: 99%

“…For single junction subcells, 90% ideal Jsc and ERE's of 1-2% have been demonstrated for III-V alloys. 5,11 Thus 50% efficiency is readily achievable for ideal filters but will require higher efficiency subcells in this case of the commercially available filters. However, very high efficiencies (>43%) are achievable with commercially available filters and show promise for high efficiency spectral splitting module architectures.…”

Section: Ere 1%1mentioning

confidence: 99%

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Polyhedral specular reflector design for ultra high spectrum splitting solar module efficiencies (>50%)

et al. 2013

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One pathway to achieving ultra-high solar efficiencies (>50%) is employing a spectrum splitting optical element with at least 6 subcells and significant concentration (100-500 suns). We propose a design to meet these criteria, employing specular reflection to split and divide the light onto appropriate subcells. The polyhedral specular reflector incorporates a high index parallelepiped with seven subcells. The subcells are placed around the parallelepiped such that light entering at normal incidence encounters the subcells in order from highest to lowest bandgap, with the ray path reflecting at a 90° angle until the light is fully absorbed. Previous studies of the design have shown that concentration and filters are necessary to achieve high efficiencies and thus the current iteration of the design employs shortpass filters and two stages of concentration. Ray tracing of the current iteration shows exceeding 50% efficiency is possible for current subcell qualities with perfect shortpass filters while 50% module efficiencies are only possible for very high quality (>6% ERE) subcells with commercially available shortpass filters. However, even with commercially available filters and achievable subcell quality, ray tracing results show very high (>43%) module efficiency.

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Energy production advantage of independent subcell connection for multijunction photovoltaics

Warmann

Atwater

2016

Energy Science & Engineering

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Increasing the number of subcells in a multijunction or "spectrum splitting" photovoltaic improves efficiency under the standard AM1.5D design spectrum, but it can lower efficiency under spectra that differ from the standard if the subcells are connected electrically in series. Using atmospheric data and the SMARTS multiple scattering and absorption model, we simulated sunny day spectra over 1 year for five locations in the United States and determined the annual energy production of spectrum splitting ensembles with 2-20 subcells connected electrically in series or independently. While electrically independent subcells have a small efficiency advantage over series-connected ensembles under the AM1.5D design spectrum, they have a pronounced energy production advantage under realistic spectra over 1 year. Simulated energy production increased with subcell number for the electrically independent ensembles, but it peaked at 8-10 subcells for those connected in series. Electrically independent ensembles with 20 subcells produce up to 27% more energy annually than the seriesconnected 20-subcell ensemble. This energy production advantage persists when clouds are accounted for. 236

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Spectrum splitting photovoltaics: Materials and device parameters to achieve ultrahigh system efficiency

Cited by 8 publications

References 10 publications

Spectrum splitting photovoltaics: Light trapping filtered concentrator for ultrahigh photovoltaic efficiency

Spectrum splitting photovoltaics: Light trapping filtered concentrator for ultrahigh photovoltaic efficiency

Polyhedral specular reflector design for ultra high spectrum splitting solar module efficiencies (>50%)

Energy production advantage of independent subcell connection for multijunction photovoltaics

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