John Schermer

Broadband and Omnidirectional Anti-reflection Coating for III/V Multi-junction Solar Cells

Graded refractive index layers reduce the reflection and increase the coupling of light into a substrate by optical impedance matching at the interfaces. Due to the optical impedance matching, reflections at the interfaces are not possible for a broad wavelength range, rendering this type of anti-reflection coating a promising candidate for III/V multi-junction solar cells. Graded refractive index layers can be modeled using a transfer-matrix method for isotropic layered media. We derive the transfer-matrix method and we show calculations of the reflection from and the transmission into an AlInP layer coated with different anti-reflection coatings. We describe a new type of anti-reflection coating based on tapered semiconductor nanowires and we show reflection and transmission measurements of those kind of anti-reflection coatings on top of different substrates.

CN distribution in flame deposition of diamond and its relation to the growth rate, morphology, and nitrogen incorporation of the diamond layer

Abstract Two-dimensional laser-induced fluorescence (2D-LIF) measurements are applied to the chemical vapour deposition (CVD) of diamond by an oxyacetylene flame to visualize the distribution of CN in the gas phase during the diamond growth process. The obtained diamond deposits are characterized by optical as well as scanning electron microscopy (SEM) and cathodoluminescence topography (CL). Experiments are carried out in both laminar and turbulent flames and show CN to be present mostly at the outer edge of the flame, where ambient air interacts with flame gases. Clear relations are observed between the distribution of CN and the local variation of the growth rate, the morphology, and the nitrogen incorporation as identified by CL in the deposited diamond layer. The observed differences between the laminar and turbulent flame can be attributed to enhanced diffusion of nitrogen into the latter. Significant differences are found between the results of experiments performed with acetylene gas bottles from two different suppliers.

Enhancement of current collection in epitaxial lift-off InAs/GaAs quantum dot thin film solar cell and concentrated photovoltaic study

We report the fabrication of a thin film InAs/GaAs quantum dot solar cell (QD cell) by applying epitaxial lift-off (ELO) approach to the GaAs substrate. We confirmed significant current collection enhancement (∼0.91u2009mA/cm2) in the ELO-InAs QD cell within the wavelength range of 700u2009nm–900u2009nm when compared to the ELO-GaAs control cell. This is almost six times of the sub-GaAs bandgap current collection (∼0.16u2009mA/cm2) from the wavelength range of 900u2009nm and beyond, we also confirmed the ELO induced resonance cavity effect was able to increase the solar cell efficiency by increasing both the short circuit current and open voltage. The electric field intensity of the resonance cavity formed in the ELO film between the Au back reflector and the GaAs front contact layer was analyzed in detail by finite-differential time-domain (FDTD) simulation. We found that the calculated current collection enhancement within the wavelength range of 700u2009nm–900u2009nm was strongly influenced by the size and shape of InAs QD. In addition, we performed concentrated light photovoltaic study and analyzed the effect of intermediate states on the open voltage under varied concentrated light intensity for the ELO-InAs QD cell.

Er3+/Yb3+ upconverters for InGaP solar cells under concentrated broadband illumination

The inability of solar cell materials to convert all incident photon energy into electrical current, provides a fundamental limit to the solar cell efficiency; the so called Shockley-Queisser (SQ) limit. A process termed upconversion provides a pathway to convert otherwise unabsorbed low energy photons passing through the solar cell into higher energy photons, which subsequently can be redirected back to the solar cell. The combination of a semi-transparent InGaP solar cell with lanthanide upconverters, consisting of ytterbium and erbium ions doped in three different host materials (Gd2O2S, Y2O3 and NaYF4) is investigated. Using sub-band gap light of wavelength range 890 nm to 1045 nm with a total accumulated power density of 2.7 kW m(-2), a distinct photocurrent was measured in the solar cell when the upconverters were applied whereas a zero current was measured without upconverter. Furthermore, a time delay between excitation and emission was observed for all upconverter systems which can be explained by energy transfer upconversion. Also, a quadratic dependence on the illumination intensity was observed for the NaYF4 and Y2O3 host material upconverters. The Gd2O2S host material upconverter deviated from the quadratic illumination intensity dependence towards linear behaviour, which can be attributed to saturation effects occurring at higher illumination power densities.

Deep junction III-V solar cells with enhanced performance

The influence of junction depth in III–V solar cell structures was investigated for GaAs and InGaP cells. Typical III–V solar cells employ a shallow junction design. We have shown that for both investigated cell types, a deep junction close to the back of the cell structure performs better than shallow junction cells. At the maximum power point the deep junction cells operate mainly in the radiative recombination regime, while in the shallow junction cells non-radiative recombination is dominant. The steeper slope of the IV curve boosts the fill-factor by 3–4%, which is thereby the most improved cell parameter. In order to minimize collection losses in the upper part of the solar cell, the optimal thickness of the GaAs deep junction cell is only two-thirds of a shallow junction cell. The associated lower cell current is more than compensated by the higher fill-factor and open circuit voltage. The best deep junction GaAs cell shows a record efficiency of 26.5% for a GaAs cell on substrate. In the thinner InGaP deep junction cell the absence of current loss, leads to 1.6% higher efficiency than for the shallow junction cell.

Temperature-Induced Degradation of Thin-Film III–V Solar Cells for Space Applications

High-efficiency, thin-film III–V solar cells offer excellent characteristics for implementation in flexible solar panels for space applications. In order to investigate the space compatibility of such cells, the temperature-induced degradation of both substrate-based cells with Au and Au/Cu contacts and thin-film cells on Au and Cu carriers was studied by accelerated ageing testing (AAT) at 200xa0<inline-formula><tex-math notation=LaTeX>

InGaP/GaAs Inverted Dual Junction Solar Cells For CPV Applications Using Metal-Backed Epitaxial Lift-Off

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Light-trapping enhanced thin-film III-V quantum dot solar cells fabricated by epitaxial lift-off

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Muscovite mica as a growth template of PC61BM crystallites for organic photovoltaics

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Effects of primary optics shading on electrical performance of CPV systems for building-integration

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