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

Abstract

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 latticematched 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/cm 2 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 μm with surface recombination velocities in close agreement to those found in bulk Ge material.

Multijunction solar cells incorporating group IV SiGeSn alloys

“…Initially, the SiGeSn alloys were grown with an ultra-high vacuum CVD on 4-inch Ge (100) substrates, with a miscut of 6° towards the <111> plane to reduce the formation of anti-phase boundaries in the subsequent MOCVD growth [6]. Before the 1.0 eV SiGeSn layer, a highly doped SiGeSn acting as back surface field was grown in order to limit the diffusion of minority carriers into the Ge inactive substrate [5]. The SiGeSn subcell was p-type doped to lxlO 18 cm" 3 .…”

“…Despite the development of this new alloy is still in its infancy, materials research is progressing and the first prototypes of operating devices have been reported [5]. Here, the characterization of a set of single and multijunction solar cells incorporating SiGeSn active junctions is presented.…”

Characterization of SiGeSn for Use as a 1 eV Sub-Cell in Multi-Junction Solar Cells

“…1 shows a possible fully lattice-matched device architecture consisting of InGaP/(In)GaAs/SiGeSn/Ge. Although functional single and triple-junction devices containing SiGeSn have been demonstrated [13], design of a high-quality 4J cell requires further insight into the fundamental properties of SiGeSn at various compositions, and high-quality material growth at the desired composition.…”

Compositional dependence of direct transition energies in Si$_x$Ge$_{1-x-y}$Sn$_y$ alloys lattice-matched to Ge/GaAs

“…Si x Ge 1−x−y Sn y ternary alloys have been a topic of research interest for a variety of applications, including group IV lasers [1,2], photodiodes [3], light-emitting diodes (LEDs) [4,5] and photovoltaics [4,[6][7][8]. By controlling the alloy composition, it is possible to tune the bandgap, higher-energy interband transitions, and the lattice constant.…”