skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Back-surface Optimization of Germanium TPV Cells

Abstract

In this work two solar cell designs have been investigated in order to improve the properties of the backside of Germanium TPV cells. In the first design. Aluminum is used as the backside contact and acts as a back surface field (BSF). The second design combines a dielectric mirror of a-Si/SiO2 with Al laser-fired point contacts (LFC). This dielectric mirror features high infrared reflection and excellent electrical passivation of the germanium back surface. Lifetime values up to 420 {mu}s have been achieved on a Germanium wafer with a resistivity of 0.5-1.5 {omega}.cm. For both solar cell designs an efficiency of 16% has been achieved assuming a microstructured tungsten emitter spectrum at 1100 deg. C with an incident radiation density of 2.5 W/cm2.

Authors:
; ; ; ;  [1]
  1. Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstr. 2, 79110 Freiburg (Germany)
Publication Date:
OSTI Identifier:
21054925
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 890; Journal Issue: 1; Conference: TPV7: 7. world conference on thermophotovoltaic generation of electricity, Madrid (Spain), 25-27 Sep 2006; Other Information: DOI: 10.1063/1.2711736; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALUMINIUM; DESIGN; DIELECTRIC MATERIALS; EFFICIENCY; ELECTRIC CONDUCTIVITY; ELECTRIC CONTACTS; GERMANIUM; INTERFACES; LIFETIME; MIRRORS; PASSIVATION; SILICON; SILICON OXIDES; SOLAR CELLS; THERMOPHOTOVOLTAIC CONVERSION; TUNGSTEN

Citation Formats

Fernandez, J., Dimroth, F., Oliva, E., Hermle, M., and Bett, A. W. Back-surface Optimization of Germanium TPV Cells. United States: N. p., 2007. Web. doi:10.1063/1.2711736.
Fernandez, J., Dimroth, F., Oliva, E., Hermle, M., & Bett, A. W. Back-surface Optimization of Germanium TPV Cells. United States. doi:10.1063/1.2711736.
Fernandez, J., Dimroth, F., Oliva, E., Hermle, M., and Bett, A. W. Thu . "Back-surface Optimization of Germanium TPV Cells". United States. doi:10.1063/1.2711736.
@article{osti_21054925,
title = {Back-surface Optimization of Germanium TPV Cells},
author = {Fernandez, J. and Dimroth, F. and Oliva, E. and Hermle, M. and Bett, A. W.},
abstractNote = {In this work two solar cell designs have been investigated in order to improve the properties of the backside of Germanium TPV cells. In the first design. Aluminum is used as the backside contact and acts as a back surface field (BSF). The second design combines a dielectric mirror of a-Si/SiO2 with Al laser-fired point contacts (LFC). This dielectric mirror features high infrared reflection and excellent electrical passivation of the germanium back surface. Lifetime values up to 420 {mu}s have been achieved on a Germanium wafer with a resistivity of 0.5-1.5 {omega}.cm. For both solar cell designs an efficiency of 16% has been achieved assuming a microstructured tungsten emitter spectrum at 1100 deg. C with an incident radiation density of 2.5 W/cm2.},
doi = {10.1063/1.2711736},
journal = {AIP Conference Proceedings},
number = 1,
volume = 890,
place = {United States},
year = {Thu Feb 22 00:00:00 EST 2007},
month = {Thu Feb 22 00:00:00 EST 2007}
}
  • Two main results are presented. The first deals with a simple method that determines the minority-carrier lifetime and the effective surface recombination velocity of the quasi-neutral base of silicon solar cells. The method requires the observation of only a single transient, and is amenable to automation for in-process monitoring in manufacturing. Distinct from many other methods in use, this method, which is called short-circuit current decay, avoids distortion in the observed transient and consequent inaccuracies that arise from the presence of mobile holes and electrons stored in the p-n junction spacecharge region at the initial instant of the transient. Themore » second main result consists in a formulation of the relevant boundary-value problems that resembles that used in linear two-port network theory. This formulation enables comparisons to be made among various contending methods for measuring material parameters of p-n junction devices, and enables the option of putting the description in the time domain in the form of an infinite series, although closedform solutions are also possible. The advantage of an infinite-series formulation is the possibility of identifying dominant relaxation times of the transient, leading thereby to simplified descriptions. By outlining the derivation of open-circuit-voltage decay and junction-current recovery from this two-port formulation, we systematically compare these methods with the short-circuit-current decay method that is emphasized here. Small-signal admittance measurement methods also emerge as special cases of the two-port formulation, as is discussed briefly.« less
  • Previously a model has been presented for calculating the performance of a TPV system. This model has been revised into a general purpose algorithm, improved in fidelity, and is presented here. The basic model is an energy based formulation and evaluates both the radiant and heat source elements of a combustion based system. Improvements in the radiant calculations include the use of ray tracking formulations and view factors for evaluating various flat plate and cylindrical configurations. Calculation of photocell temperature and performance parameters as a function of position and incident power have also been incorporated. Heat source calculations have beenmore » fully integrated into the code by the incorporation of a modified version of the NASA Complex Chemical Equilibrium Compositions and Applications (CEA) code. Additionally, coding has been incorporated to allow optimization of various system parameters and configurations. Several examples cases are presented and compared, and an optimum flat plate emitter/filter/photovoltaic configuration is also described. {copyright} {ital 1997 American Institute of Physics.}« less
  • Al-SiO/sub x/-pSi MIS solar cells have been fabricated on 10-..cap omega.. cm substrates both with and without back surface fields. The back-surface-field structure has been found to significantly enhance the open-circuit voltage of these cells, and V/sub oc/ values in excess of 580 mV have been recorded at photocurrent densities of 300 A m/sup -2/. These results provide further evidence that MIS diodes can be produced in which the dark current is dominated by minority-carrier flows.
  • Absorption spectra and redox potentials in acid solution limit sunlight engineering efficiency (S.E.E.) of unsensitized iron-thiazine photogalvanic cells to approx. 2%. The highest S.E.E. value obtained with totally illuminated single thin-layer (TI-TL) iron-thionine cells with SnO/sub 2/ anodes and Pt cathodes, .036%, corresponds to V/sub power point/ approx. 35% of theoretical limit. Potentials at the selective anode are dominated by the dye-leucodyne couple. Potentials at the poorly selective cathode are dominated by the iron couple. I/sub sc/ varies linearly with photostationary concentration of leucothionine and with electrode spacing less than or equal to 50 ..mu..m, is not limited by solutionmore » lifetime of charge carriers. Inefficient electron transfer at the electrodes is believed to reduce S.E.E. by a factor of approx. 5, possibly because of surface-promoted back reaction on SnO/sub 2/. 18 references.« less
  • Recent research has shown that negative-barrier metal insulator semiconductor (MIS) contacts can exhibit the same minority-carrier reflecting properties as diffused back-surface field regions. This letter describes the use of negative-barrier platinum-MIS contacts to form the first induced back-surface field solar cells on p-type silicon substrates.Pt-SiO/sub x/ -pSi back contacts have been applied both to cells with diffused front junctions and to cells with minority-carrier injecting MIS front junctions. In both cases an enhancement in open-circuit voltage comparable to that obtained with diffused back-surface fields has been observed. The negative-barrier MIS contact has also been found to increase the infrared photocurrent.