Radek Roucka

Demonstrating Dilute-Tin Alloy SiGeSn for Use in Multijunction Photovoltaics: Single- and Multijunction Solar Cells With a 1.0-eV SiGeSn Junction

SiGeSn ternary alloys offer a means to fabricate a 1.0-eV subcell junction for inclusion in a multijunction solar cell. The main advantage of the SiGeSn alloy is a tuneable bandgap energy and variable lattice parameter, enabling the material to be integrated into the existing lattice-matched multijunction architectures. Recent growth, structural, optical, and device results from SiGeSn material, with energy gaps in the vicinity of 1.0 eV and lattice matched to Ge substrates, are presented. An all lattice-matched InGaP/InGaAs/SiGeSn triple-junction cell is presented and compared with a conventional InGaP/InGaAs/Ge solar cell. Comparable short-circuit current values of 13.9 mA/cm2 are obtained for both devices under the AM1.5G spectrum, whereas the open-circuit voltage and fill factor are reduced in the device with the SiGeSn subcell. Peak external quantum efficiency in the SiGeSn single junction in excess of 80% is realized, placing a lower limit on the base minority hole diffusion length of 5

Single and multi-junction solar cells utilizing a 1.0 eV SiGeSn junction

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Rare-earth-metal oxide buffer for epitaxial growth of single crystal GeSi and Ge on Si(111)

m with surface recombination velocities in close agreement to those found in bulk Ge material.

3J solar cells comprising a lattice matched epitaxial SiGeSn subcell

Multi-junction photovoltaic technologies lead the way to achieving ultra-high power conversion efficiencies for both space based and terrestrial concentrator applications. However, realizing a lattice matched quad-junction solar cell remains challenging due to a lack of suitable material systems able to achieve the elusive middle sub-cell band-gap energy of 1.0 eV. In this work, we present a potential candidate material to achieve this 1.0 eV sub-cell, the group–IV ternary alloy SiGeSn. Initial simulations of triple and quadruple junction solar cell designs show that this novel material system has the potential to reach efficiencies in excess of 45 and 48% respectively under concentrated illumination. We report on the electrical characterization of both single and triple junction devices based on a 1.0 eV SiGeSn junction. It is shown that the external quantum efficiency performance of both SiGeSn devices is promising given the initial state of development of the alloy, with a fitted minority electron diff...

Single and multijunction solar cells with 1.0 eV Si-Ge-Sn junction

Ternary and binary rare-earth oxides that are used as a template buffer, which accommodates the crystal lattice mismatch between substrate and a semiconductor layer, are discussed here. The oxides were grown on Si(111) substrates and exhibit the cubic bixbyite crystal structure. Stabilization of the cubic bixbyite structure of ternary erbium-neodymium oxide and lanthanum oxide was analyzed using structural investigation of the epitaxially grown oxides and ab initio density functional theory calculations. The authors demonstrate that despite the more energetically favorable hexagonal structure of bulk lanthanum oxide a pseudomorphic single crystal cubic lanthanum oxide layer grows under nonequilibrium conditions of a molecular beam epitaxy process on gadolinium oxide. Growth of hexagonal lanthanum oxide begins when the critical thickness of the layer is reached. Germanium was epitaxially grown on the cubic bixbyite lanthanum sesquioxide. Due to a higher surface energy, germanium starts to grow in the form ...

Iv material photonic device on dbr

The performance of quad-junction Ge based III-V multi-junction solar cells depends upon successful integration of a 1.0eV sub-cell into the existing InGaP/In0.01GaAs/Ge stack. The SiGeSn ternary alloy offers a means to fabricate a lattice-matched, 1.0eV sub-cell with the advantage that SiGeSn has both a tuneable band-gap and variable lattice parameter, enabling the material to be integrated into lattice-matched multi-junction architectures. A 1eV SiGeSn junction has been grown as both a single junction device and as the third junction in a InGaP/In0.01GaAs/SiGeSn triple junction device. The SiGeSn junction produces sufficient current to almost current match the InGaP and In0.01GaAs junctions and achieves a peak external quantum efficiency > 80% is demonstrated suggesting a lower limit on the base minority hole diffusion length of 5m. However, a degradation in open-circuit voltage and fill factor are observed with the SiGeSn sub-cell. This low voltage from the SiGeSn subcell is is attributed to recombination from defect levels within the SiGeSn band gap.

Growth and application of epitaxial heterostructures with polymorphous rare-earth oxides

Recent development of Si-Ge-Sn ternary alloys offers an alternative to 1.0 eV bandgap materials for multijunction solar cells. Main advantages of these alloys are tunable gap energy and variable lattice parameter, which can be fitted into the existing designs, thus resulting in a lattice matched solution. Recent growth, optical and structural results from Si-Ge-Sn with ~ 1 eV gaps and lattice matched to Ge substrates are presented. Based on simple device models, prototype single and triple junction cells with SiGeSn junction have been fabricated. Device measurements show that the performance of Si-Ge-Sn material is comparable to other 1.0 eV semiconductors.