Inverted High-efficieInverted High-efficiency Triple-junction Sncy Triple-junction Solar Cells Based on Golar Cells Based on GaAs SubstratesaAs SubstratesEECS 235 Paper Review EECS 235 Paper Review

PresentationPresentationXiaojun ZhangXiaojun Zhang

Papers ReviewedPapers Reviewed1.1. J.F. Geisz, S. Kurtz, et al, High-efficienJ.F. Geisz, S. Kurtz, et al, High-efficiency GaInP/GaAs/InGaAs triple-junction solacy GaInP/GaAs/InGaAs triple-junction solar cells grown inverted with a metamorphic r cells grown inverted with a metamorphic bottom junction, Appl. Phys. Lett. 91, 0235bottom junction, Appl. Phys. Lett. 91, 023502 (2007)02 (2007)2.2. J.F. Geisz, D.J. Friedman, et al, 40.8% J.F. Geisz, D.J. Friedman, et al, 40.8% efficient inverted triple-junction solar cell efficient inverted triple-junction solar cell with two independently metamorphic juncwith two independently metamorphic junctions, Appl. Phys. Lett. 93, 123505 (2008)tions, Appl. Phys. Lett. 93, 123505 (2008)

Triple-junction Solar Triple-junction Solar CellsCells

Theoretical Bandgaps: Eg1 = 1.86 eV; Eg2 = 1.34 eV; Eg3 = 0.93 eV

Schematic of an inverted Schematic of an inverted triple-junction solar celltriple-junction solar cell

Grow

th D

irection

Why inverted?Why inverted? The top cell produces more power The top cell produces more power

than the lower ones. Importance: than the lower ones. Importance: Cell 1 > Cell 2> Cell 3.Cell 1 > Cell 2> Cell 3.

By inverting the growth sequence, By inverting the growth sequence, the top layers, which are more the top layers, which are more important, can be grown first and important, can be grown first and thus have a better quality.thus have a better quality.

In order to achieve high In order to achieve high efficiencyefficiency

Two important factors to be consideredTwo important factors to be considered Lattice MatchLattice Match Bandgap Match (Theoretical Bandgaps:Bandgap Match (Theoretical Bandgaps: 1.86 eV; 1.34 eV; 0.93 eV)

In order to achieve high In order to achieve high efficiencyefficiency

Considering bandgap match (Considering bandgap match (1.86 eV; 1.34 eV; 0.93 eV ): ): GaInP/GaInAs/Ge : 1.86 eV, 1.39 eV, 0.67 eV, Ge, not good! Ga0.5In0.5P/GaAs/In0.3Ga0.7As: 1.8 eV; 1.4 eV, 1.0 eV (paper 1), Acceptable! Ga0.51In0.49P/In0.04Ga0.96As/In0.37Ga0.63As: 1.83 eV; 1.34 eV; 0.89 eV (paper 2), Best!

ExperimentalsExperimentals Grown by atmospheric-pressure organometallic vapor phase epitaxy (OMVPE) on a (001) GaAs substrate. Gold was electroplated. The sample was then mounted to a handle with epoxy. The GaAs substrate was removed using selective chemical etching. Antireflective coating and gold grids on the front layer were deposited.

ResultsResults

Paper 1 Paper 2Test results under the direct terrestrial spectrum as a function of concentration

Thank you!Thank you!Any questions?Any questions?