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Title: Optimized III-V Multijunction Concentrator Solar Cells on Patterned Si and Ge Substrates: Final Technical Report, 15 September 2004--30 September 2006

Abstract

Goal is to demo realistic path to III-V multijunction concentrator efficiencies > 40% by substrate-engineering combining compositional grading with patterned epitaxy for small-area cells for high concentration.

Authors:
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
942086
Report Number(s):
NREL/SR-520-44250
XAT-4-33624-14; TRN: US200902%%89
DOE Contract Number:
AC36-99-GO10337
Resource Type:
Technical Report
Resource Relation:
Related Information: Work performed by The Ohio State University, Columbus, Ohio
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; BUFFERS; CONCENTRATION RATIO; CONCENTRATOR SOLAR CELLS; CONCENTRATORS; DISLOCATIONS; EFFICIENCY; EPITAXY; RESEARCH PROGRAMS; SOLAR CELLS; SUBSTRATES; THERMAL CONDUCTIVITY; PV; III-V MULTIJUNCTION CONCENTRATOR; GE SUBTRATE; LATTICE MATCH; DUAL JUNCTION; PATTERNED SI:GE/SI; COMPOSITIONAL GRADING; INGAP/INGAAS; SMALL AREA; Solar Energy - Photovoltaics

Citation Formats

Ringel, S. A. Optimized III-V Multijunction Concentrator Solar Cells on Patterned Si and Ge Substrates: Final Technical Report, 15 September 2004--30 September 2006. United States: N. p., 2008. Web. doi:10.2172/942086.
Ringel, S. A. Optimized III-V Multijunction Concentrator Solar Cells on Patterned Si and Ge Substrates: Final Technical Report, 15 September 2004--30 September 2006. United States. doi:10.2172/942086.
Ringel, S. A. Sat . "Optimized III-V Multijunction Concentrator Solar Cells on Patterned Si and Ge Substrates: Final Technical Report, 15 September 2004--30 September 2006". United States. doi:10.2172/942086. https://www.osti.gov/servlets/purl/942086.
@article{osti_942086,
title = {Optimized III-V Multijunction Concentrator Solar Cells on Patterned Si and Ge Substrates: Final Technical Report, 15 September 2004--30 September 2006},
author = {Ringel, S. A.},
abstractNote = {Goal is to demo realistic path to III-V multijunction concentrator efficiencies > 40% by substrate-engineering combining compositional grading with patterned epitaxy for small-area cells for high concentration.},
doi = {10.2172/942086},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sat Nov 01 00:00:00 EDT 2008},
month = {Sat Nov 01 00:00:00 EDT 2008}
}

Technical Report:

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  • This report deals with research and development on materials pertinent to the multigap approach to high efficiency solar cells. Initial investigations were confined to the two-gap version, and most of the work was concerned with the InGaAs (0.73 eV) and Ge (0.67 eV) semiconductors that potentially could be used as a lower junction cell to capture the radiation passing through an AlGaAs/GaAs (1.425 eV) upper cell. In addition, some work leading to the realization of the optimum bandgap configuration (1.65 and 1.15 eV) for an optimized two-junction tandem solar cell is reported.
  • This report describes research performed in several areas of AlGaAs/GaAs cascade technology. Annealing studies of p/sup +/-Ge layers grown on p/sup +/-GaAs substrates indicate that the Ge-GaAs interfaces are adequately stable to interdiffusional mixing if the interface thermal stress is limited to about 700/degree/C for 1 hour. Specific resistivities of intercell ohmic connections (IOC) remain below the goal of 2 /times/ 10/sup -4/ ohm-cm/sup 2/. The thermal stability of the IOC dictates a growth-temperature limit for the AlGaAs top cell significantly lower than conventional organometallic vapor-phase epitaxial practice. Growing high-quality AlGaAs junctions at 700/degree/C or lower caused some difficulty. Minority-carrier-lifetimemore » degradation was studied, but the causes of lifetime reduction remain largely unidentified. Selective epitaxy of the Ge IOC was developed. Slow etching resulted in substantial under-cutting of photolithographic patterns and created problems with reproducibility. The use of MCPMg appears to be suitable for p-type doping in both GaAs and AlGaAs cell growth. Causes of the relatively poor performance of AlGaAs grown at low temperatures merit further research, since this system is important for solar cells. 13 refs., 16 figs., 4 tabs.« less
  • In high growth rate ({ge} 50 {angstrom}/s) HW-CVD a-Si:H films, for the first time, we show gaseous molecules in nanovoids ({approx}2% volume fraction of tube-like nanoscale voids), and demonstrate that confinement on the nanometer scale generates NMR effects that have never been observed in macroscopic systems. In the same system we found the PL peak red shift. We suggest that highly strained bonds on the inner surfaces of the nanoscale voids form broad conduction-band tail states that are responsible for the PL red shift. We characterized the structural transition from a- to nc-Si as function of H-dilution, thickness and T{submore » s} of both HW- and PE-CVD films using IR, Raman, PL, CPM/PDS and E{sub a} et al. We found not only the c-Si volume fraction but also the g.b. and microstructures play an important role in the properties of the i-layer and their solar cell performance. We found a narrow structural transition zone in which the bond-angle variation, {Delta}{Theta}, decreases from 10{sup o} to 8{sup o}. For nc-Si samples, we found a characteristic low energy PL peak and proved that is originated from the g.b. regions. Using micro-Raman, we found the structural non-uniformity in the mixed-phase solar cells that showed V{sub oc} enhancement after light soaking. Using micro-Raman, we also found the slight increase of crystallinity in M/{mu}c-Si/M devices after current forming.« less
  • The objective was to develop a simple theoretical model based on Wilson's model to calculate the displacement damages introduced by either protron or electron irradiation in AlGaAs, GaAs, InGaAs and Ge. These calculations would then be applied to obtain an optimized triple-junction solar-cell structure using these materials with a specified end of life conversion efficiency. Empirical formulae and theoretical expressions were derived for calculating the displacement cross section, penetration depth, path length, total number of defects formed by an incident electron or protron, and the fractional loss of electron-hole pairs due to recombination loss. Formulae to calculate the degradation ofmore » short-circuit current under different electron and proton fluences and energies in AlGaAs, GaAs, InGaAs, Ge single junction solar cells and the triple junction cells formed from these materials were developed. The results of our calculations indicate that the degradation rate in each cell varies greatly, and depends critically not only the energy, fluence, and the direction of the incident electrons and protons but also on the thickness of each cell in the triple-junction cells. Major difficulties encountered in performing the theoretical calculations using the model developed in this report included may unknown parameters and the lack of experimental data on electron and proton damages in the AlGaAs and InGaAs solar cells for comparison with theoretical calculations. These uncertainties can be removed once the actual cell structures for the proposed triple-junction cells are fabricated and measurements of radiation damage are made in these cells.« less
  • The goal of this research is to demonstrate a two-junction cascade solar cell, 0.5 cm/sup 2/ in area, in the AlGaAs-GaAs material system that has a power conversion efficiency of more than 30% at a cell temperature of 50/sup 0/C. Objectives for the first year of the program included growth of Al/sub x/Ga/sub 1-x/As on Al/sub y/Ga/sub 1-y/As exposed to air for at least one hour; growth of Ge by vapor phase epitaxy on a GaAs substrate; fabrication of a p/n patterned Ge tunnel junction grown on n-GaAs and demonstration of a current density larger than 80 A/cm/sup 2/; growthmore » and characterization of a top cell on a patterned Ge tunnel junction; and fabrication and demonstration of an AlGaAs-GaAs cascade solar cell using the patterned Ge tunnel junction. A patterned Ge-tunnel junction connecting the n-type base region of a GaAs cell to a p/sup +/-GaAs substrate was demonstrated for the first time.« less