We have developed thin film amorphous silicon alloy (a-Si:H) and nanocrystalline silicon (nc-Si:H) based multijunction solar cells on lightweight polymer substrate ~25 μm thick for space and ...near-space applications. The baseline cells use an a-Si:H/a-SiGe:H/a-SiGe:H structure deposited by conventional Radio Frequency (RF) plasma enhanced CVD using roll-to-roll deposition. The best initial performance for the baseline cells is aperture-area efficiency 9.84% and specific power ~1200 W/kg. The baseline cells are available to potential customers in large quantities. In order to increase the solar cell efficiency, we have pursued two new approaches. In the first, we use a Modified Very High Frequency (MVHF) technique to deposit the multijunction a-SiGe:H based cells. In the second, we have investigated nc-Si:H based multijunction cells. In this paper, we present the solar cell efficiency results on the three different device structures.
We present our progress in attaining high efficiency nc-Si:H solar cells at high deposition rates with superior light soaking stability. We have focused our effort on three areas: (i) improving the ...spatial uniformity and homogeneous properties for nc-Si:H, such as crystallite grain size and volume fraction, (ii) optimizing nucleation and seed layer during the initial growth of the nc-Si:H film, and (iii) optimizing nc-Si:H bulk growth and grain evolution. We have conducted an extensive study of the effect of process parameters including hydrogen dilution profiling, VHF power, and substrate temperature on the nc-Si:H film properties and component cell characteristics. We also conducted light soaking tests both indoors and outdoors. The a-Si:H/nc-Si:H/nc-Si:H triple-junction cells incorporating the optimized nc-Si:H component cells show significantly higher performance, achieving an 11.2% AM1.5 stabilized efficiency for both encapsulated large-area (464 cm 2 ) cells and inter-connected modules (2320 cm 2 ). To the best of our knowledge, this is the highest stabilized efficiency for a large-area thin-film silicon module.
The short-wavelength limits of AlGaInP visible laser diodes with Al/sub 0.5/In/sub 0.5/P cladding layers, and Ga/sub x/In/sub 1/spl minus/x/P single quantum well (QW) active regions are investigated. ...Good performance is maintained throughout the 620 nm band, but the characteristics rapidly degrade in the 610 nm band. Biaxial-compression and -tension were compared, with the case of tension yielding slightly better performance. Using a 25 /spl Aring/ Ga/sub 0.45/In/sub 0.55/P QW, a wavelength of 614 nm was obtained, while a 50 /spl Aring/ Ga/sub 0.6/In/sub 0.4/P QW emitted at 620 nm with a threshold current density of 0.8 kA/cm/sup 2/. These results with thin single QWs indicate the effectiveness of using an Al/sub 0.5/In/sub 0.5/P cladding layer to reduce electron leakage.< >
Electrical performance degradation of a-Si/a-SiGe/a-SiGe triple-junction solar cells due to irradiation of protons with different energies and their performance recovery at room temperature just ...after irradiation are reported. The current-voltage characteristics are measured in-situ and the results show that all the parameters recover with time after proton irradiation is stopped. In particular, the short-circuit current remarkably recovers. It is also shown that the degradation is scaled by a unit of displacement damage dose independent of proton energy. This indicates that the proton-induced degradation is mainly caused by the displacement damage effect.
A single quantum-well Ga/sub 0.5+/spl delta//In/sub 0.5-/spl delta//P/(AlGa)/sub 0.5/In/sub 0.5/P laser structure is demonstrated, which can provide similar gain in both polarizations. The slightly ...tensile-strained quantum-well has a light-hole ground state, which gives the lowest transparency current for TM-mode gain. However, the TE-mode gain is dominant at high drive currents. The gain-current relationships have been characterized for each polarization, and found to cross at a modal gain value of 25 cm/sup -1/. Lasers whose threshold gain is near this crossover value were found to emit in either one or both polarizations, with a very wide range of polarization asymmetry possible. A simple QW gain model can be used to qualitatively describe this behavior, along with the tendency toward TE-mode emission at higher temperature.< >
A method for incorporating distributed feedback in a ridge waveguide laser by means of lateral gratings and a single growth step is discussed. The necessary Bragg condition for distributed feedback ...is satisfied by etching gratings along the ridge in the top confining layer of the laser on either side of the contact stripe. Both Fabry-Periot modes and a single emission peak away from the peak of the gain profile are observed in lasers with cleaved facets. The Bragg reflection emission peak does not shift with increasing drive current, which is characteristic of a distributed-feedback (DFB) laser.< >
The design and operation of InGaAs-GaAs-AlGaAs asymmetric cladding ridge waveguide distributed Bragg reflector lasers is presented. Targeted for the remote sensing of water vapor with absorption ...lines in the /spl lambda//spl sim/930 nm region, these devices operate CW with threshold currents as low as 11 mA and slope efficiencies as high as 0.37 W/A. They also operate with over 30-dB side-mode suppression, and the typical CW characteristic temperature, T/sub 0/, is 95 K.
The performance of a novel ridge-waveguide, distributed-Bragg-reflector laser was tested for spectroscopic remote sensing applications. The laser exhibits a narrow linewidth, excellent side-mode ...suppression, and flexible, highly repeatable wavelength tuning. These characteristics are significant improvements over current Fabry-Perot lasers, and indicate that distributed-Bragg-reflector lasers are promising candidates for implementing advanced semiconductor-based optical remote sensing systems.
InGaAs-GaAs-AlGaAs strained-layer distributed-feedback (DFB) ridge-waveguide lasers requiring a single metalorganic chemical vapor deposition (MOCVD) growth step are shown to operate in a single ...longitudinal mode up to 2.2*I/sub th/ with an antireflection (AR) coating applied to one facet under room temperature, pulsed conditions. A value of kL=0.33 has been determined from threshold gain calculations for coated and uncoated devices. Weak lateral optical confinement, provided by unpumped lateral gratings is demonstrated by the absence of antiguiding effects, and a real lateral index step of approximately 4*10/sup -3/ is determined from near-field emission patterns.< >
United Solar Ovonic (USO) has developed a-Si:H based solar cells on polymer substrate using high-throughput roll-to-roll deposition technology for space and stratospheric missions. In addition, we ...have advanced two new developments: (1) the monolithically laser-integrated module on flexible polymer substrate to attain an initial specific power as high as 2343 W/kg at the module level; and (2) a new monolithic hybrid module design which marries the advantages of our wire bonded baseline space cell with those of the advanced laser integrated module. It uses standard production cells as the starting material and therefore it is roll-to-roll compatible. With this design, we have fabricated modules having initial AM0 aperture area efficiency ~9.5%. It operates with high voltage and high specific power. It is flexible, modular and easily scalable. The modules can be interconnected into strings and arrays that can be rolled up into a small volume for stowage.
