摘要:

This talk reviews experimental work to develop a detailed understanding of radiative recombination inn‐GaAs. Photoluminescence decay studies of minority carrier lifetimes versus doping inn‐GaAs are presented. We show that when the substrate is removed by etching, photon recycling is enhanced, and lifetimes increase by nearly a factor of 10. The doping‐dependent absorption coefficient is measured, and detailed balance arguments are used to relate absorption and recombination. Modeling surfaces, verified by comparison with experiments, are used to examine the effects of recycling in conventional solar cells and to explore new design options.

ISSN:0094-243X    

DOI:10.1063/1.42880

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

This paper reports advances in the development of solar cells made from GaAs‐on‐Si structures prepared by metalorganic chemical vapor deposition (MOCVD). The use of concentrator cells, operating at ∼200 suns, has led to the efficiency achievements of 21.3% (AM1.5D) for a GaAs‐on‐Si solar cell, and 27.6 (AM1.5D) for a homoepitaxial GaAs cell. The development of epitaxial multilayer dielectric mirrors (Bragg reflectors), as back‐surface reflectors in thin‐film GaAs cells, on both Si and GaAs substrates, is shown to lead to modest efficiency increases, over that of conventional designs.

ISSN:0094-243X    

DOI:10.1063/1.42881

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Quaternary semiconductor compounds are ideal candidates for use in monolithic cascade solar cells because the lattice constant and the bandgap of such compounds can be independently varied. The quaternary semiconductor compound Ga0.83In0.17As0.67P0.33not only is lattice matched to GaAs and Ge but also provides a current matched top cell for the GaInAsP/Ge monolithic cascade solar cell. Under concentration of 100 suns, the projected efficiency for such a cell is about 34%. The growth of Ga0.83In0.17As0.67P0.33lattice matched to GaAs and Ge has been demonstrated. GaInAsP solar cells have been grown on both GaAs and Ge substrates. A GaInAsP on GaAs solar cell with an active area efficiency of 23.2% for 1 sun, AM 1.5 direct illumination has been prepared. A proposed structure for the GaInAsP/Ge cascade cell is also given.

ISSN:0094-243X    

DOI:10.1063/1.42882

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Inverted growth and the development of associated cell processing, are likely to offer a significant degree of freedom for improving the performance of many III‐V multijunction cascades and open new avenues for advanced multijunction concepts. This is especially true for the development of high‐efficiency Al0.37Ga0.63As/GaAs cascades where the high growth temperatures required for the AlGaAs top cell growth can cause the deterioration of the tunnel junction interconnect. In the approach of inverted‐grown AlGaAs/GaAs cascade cells, the AlGaAs top cell is grown first at 780 °C and the GaAs tunnel junction and bottom cell are grown at 675 °C. After the inverted growth, the AlGaAs/GaAs cascade structure is selectively removed from the parent substrate. The feasibility of inverted growth is demonstrated by a fully‐processed, inverted‐grown, thin film GaAs cell with a 1‐sun AM1.5 efficiency of 20.3%. Also, an inverted‐grown, thin‐film, Al0.34Ga0.66As/GaAs cascade with AM1.5 efficiencies of 19.9% and 21% at 1‐sun and 7‐suns, respectively, has been obtained.

ISSN:0094-243X    

DOI:10.1063/1.42883

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The various factors that affect the open‐circuit voltage (Voc) of a two‐terminal GaInP2/GaAs tandem cell are examined. These include a) an anomalous problem associated with the GaAs bottom cell and b) back surface passivation of the thin GaInP2top cell. Solutions to these problems are presented and yield tandemVocs close to the practical theoretical limits.

ISSN:0094-243X    

DOI:10.1063/1.42884

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The band gap of Ga0.52In0.48P varies considerably, depending on conditions of growth. This is a result of ordering in the CuPt structure. Details of the ordering also lead to more subtle optical effects. We report here on photoluminescence (PL) and photoluminescence excitation (PLE) measurements on ordered and disordered Ga0.52In0.48P. The dominant high energy emission process in disordered GaInP has been established to be excitonic, but the exciton trapping energy is not unique. PLE from ordered Ga0.52In0.48P shows significant tailing of electronic states and a ‘‘band edge’’ which depends on detection energy.

ISSN:0094-243X    

DOI:10.1063/1.42885

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Ap+‐AlGaAs/n+‐GaInP heterojunction tunnel diode with band gapEg≊1.9 eV was fabricated by Atomic Layer Epitaxy growth mode using carbon and selenium as thep‐ andn‐type dopants, respectively. The doping levels of 1×1020/cm3and 5×1019/cm3were achieved both in thep‐ andn‐side of the diode, respectively. The diode can be used as the interconnection of the high and low band gap cells in the AlGaAs/GaAs cascade solar cell structure. At the forward current of 15 A/cm2, which is the expected current density at 1000 suns operation, there is only ∼17 mV voltage drop across the tunnel junction. This is the first reported tunnel diode fabricated in high band gap material systems, with performances that exceed the best reported GaAs tunnel diode.

ISSN:0094-243X    

DOI:10.1063/1.42886

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Amorphous silicon is a thin film option that has the potential for a cost‐effective product for large‐scale utility photovoltaics application. The initial efficiencies for single‐junction and multijunction amorphous silicon cells and modules have increased significantly over the past 10 years. The emphasis of research and development has changed to stabilized efficiency, especially that of multijunction modules. NREL has measured 6.3%–7.2% stabilized amorphous silicon module efficiencies for U.S. products, and 8.1% stable efficiencies have been reported by Fuji Electric. This represents a significant increase over the stabilized efficiencies of modules manufactured only a few years ago. An increasing portion of the amorphous silicon U.S. government funding is now for manufacturing technology development to reduce cost. The funding for amorphous silicon for photovoltaics by Japan over the last 5 years has been about 50% greater than that in the United States, and by Germany in the last 2–3 years more than twice that of the U.S. Amorphous silicon is the only thin‐film technology that is selling large‐area commercial modules. The cost for amorphous silicon modules is now in the $4.50 range; it is a strong function of plant production capacity and is expected to be reduced to $1.00–1.50/Wpfor plants with 10 MW/year capacities.

ISSN:0094-243X    

DOI:10.1063/1.42888

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Small‐angle x‐ray scattering (SAXS) measurements are being made to probe the microstructures on a scale from about 1 to 25 nm of amorphous silicon and silicon‐based alloy films prepared in several laboratories using a variety of deposition techniques. Assuming a film structure composed of voids dispersed in an amorphous network of constant density, volume fractions of the voids (Vf) are determined while measurements of the films at various tilt angles relative to the x‐ray beam gives information on the shapes and orientations of the voids. Fora‐Si:H films deposited using the rf glow discharge method at conditions similar to those used for preparing device quality material, Vfvalues are between 1 and 2% with most of the voids being very small (around 1 nm) and either spherical in shape or randomly oriented throughout the sample. Films made under conditions which are not optimized with respect to the photoelectronic properties contain larger voids which are elongated and preferentially oriented, suggestive of a columnar structure. Vffor a small set ofa‐Si:H samples prepared by electron cyclotron resonance and dc sputtering techniques are higher than the smallest values found for the rf glow discharge produced material. Larger Vfand preferentially oriented, elongated voids are found in all of thea‐SiGe:H films examined and in some of thea‐SiC:H materials.

ISSN:0094-243X    

DOI:10.1063/1.42889

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Ina‐Si:H photoluminescence (PL) has been measured as a function of the energy of excitation using excitation energies down to well below the optical gap. The relative quantum efficiency for PL at a specific energy increases as the excitation energy decreases. The results are interpreted in terms of a phonon assisted absorption mechanism. Ina‐Si1−xNx:H the PL spectrum and the fatigue of the PL have been measured at 300 K. The possibility that the defect states ina‐Si1−xNx:H possess a negative effective electron‐electron correlation energy is critically examined.

ISSN:0094-243X    

DOI:10.1063/1.42890

出版商:AIP    

年代:1992

数据来源: AIP