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  • 1
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    Status of Diffused Junction p(+)n InP Solar Cells for Space Applications (1994)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Recently, we have succeeded in fabricating diffused junction p(+)n(Cd,S) InP solar cells with measured AMO, 25 C open circuit voltage (V(sub OC)) of 887.6 mV, which, to the best of our knowledge, is higher than previously reported V(sub OC) values for any InP homojunction solar cells. The experiment-based projected achievable efficiency of these cells using LEC grown substrates is 21.3%. The maximum AMO, 25 C efficiency recorded to date on bare cells is, however, only 13.2%. This is because of large external and internal losses due to non-optimized front grid design, antireflection (AR) coating and emitter thickness. This paper summarizes recent advances in the technology of fabrication of p(+)n InP diffused structures and solar cells, resulted from a study undertaken in an effort to increase the cell efficiency. The topics discussed in this paper include advances in: 1) the formation of thin p(+) InP:Cd emitter layers, 2) electroplated front contacts, 3) surface passivation and 4) the design of a new native oxide/AI203/MgF2 three layer AR coating using a chemically-grown P-rich passivating oxide as a first layer. Based on the high radiation resistance and the excellent post-irradiation annealing and recovery demonstrated in the early tests done to date, as well as the projected high efficiency and low-cost high-volume fabricability, these cells show a very good potential for space photovoltaic applications.
    Keywords: Energy Production and Conversion
    Type: Proceedings of the 13th Space Photovoltaic Research and Technology Conference (SPRAT 13); 63-79; NASA-CP-3278
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  • 2
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    Thermally stable, low resistance contact systems for use with shallow junction p(+) nn(+) and n(+)pp(+) InP solar cells (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Two contact systems for use on shallow junction InP solar cells are described. The feature shared by these two contact systems is the absence of the metallurgical intermixing that normally takes place between the semiconductor and the contact metallization during the sintering process. The n(+)pp(+) cell contact system, consisting of a combination of Au and Ge, not only exhibits very low resistance in the as-fabricated state, but also yields post-sinter resistivity values of 1(exp -7) ohms-sq cm, with effectively no metal-InP interdiffusion. The n(+)pp(+)cell contact system, consisting of a combination of Ag and Zn, permits low resistance ohmic contact to be made directly to a shallow junction p/n InP device without harming the device itself during the contacting process.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: ESA, Proceedings of 4th European Space Power Conference (ESPC). Volume 2: Photovoltaic Generators, Energy Storage; p 347-350
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  • 3
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    Progress in p(+)n InP solar cells fabricated by thermal diffusion (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The performance results of our most recently thermally diffused InP solar cells using the p(+)n (Cd,S) structures are presented. We have succeeded in fabricating cells with measured AMO, 25 C V(sub oc) exceeding 880 mV (bare cells) which to the best of our knowledge is higher than previously reported V(sub oc) values for any InP homojunction solar cells. The cells were fabricated by thinning the emitter, after Au-Zn front contacting, from its initial thickness of about 4.5 microns to about 0.6 microns. After thinning, the exposed surface of the emitter was passivated by a thin (approximately 50A) P-rich oxide. Based on the measured EQY and J(sub sc)-V(sub oc) characteristics of our experimental high V(sub oc) p(+)n InP solar cells, we project that reducing the emitter thickness to 0.3 microns, using an optimized AR coating, maintaining the surface hole concentration of 3 x 10(exp 18)cm(sup -3), reducing the grid shadowing from actual 10.55 percent to 6 percent and reducing the contact resistance will increase the actual measured 12.57 percent AMO 25 C efficiency to about 20.1 percent. By using our state-of-the-art p(+)n structures which have a surface hole concentration of 4 x 10(exp 18)cm(sup -3) and slightly improving the front surface passivation, an even higher practically achievable AMO, 25 C efficiency of 21.3 percent is projected.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: Proceedings of the 12th Space Photovoltaic Research and Technology Conference (SPRAT 12); p 23-32
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  • 4
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    Status of diffused junction p+n InP solar cells for space applications (1994)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Recently, we have succeeded in fabricating diffused junction p(sup +)n(Cd,S) InP solar cells with measured AMO, 25 C open circuit voltage (V(sub OC)) of 887.6 mV, which, to the best of our knowledge, is higher than previously reported V(sub OC) values for any InP homojunction solar cells. The experiment-based projected achievable efficiency of these cells using LEC grown substrates is 21.3 percent. The maximum AMO, 25 C internal losses due to date on bare cells is, however, only 13.2 percent. This is because of large external and internal losses due to non-optimized front grid design, antireflection (AR) coating and emitter thickness. This paper summarizes recent advances in the technology of fabrication of p(sup +)n InP diffused structures and solar cells, resulted from a study undertaken in an effort to increase the cell efficiency. The topics discussed in this paper include advances in: (1) the formation on thin p(sup +) InP:Cd emitter layers, (2) electroplated front contacts, (3) surface passivation and (4) the design of a new native oxide/Al2O3/MgF2 tree layer AR coating using a chemically-grown P-rich passivating oxide as a first layer. Based on the high radiation resistance and the excellent post-irradiation annealing and recovery demonstrated in the early tests done to date, as well as the projected high efficiency and low-cost high-volume fabricability, these cells show a very good potential for space photovoltaic applications.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: Proceedings of the 13th Space Photovoltaic Research and Technology Conference (SPRAT 13); p 63-79
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  • 5
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    Progress in p(+)n InP solar cells fabricated by thermal diffusion (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: In SPRAT XI, we proposed that p(sup +)n diffused junction InP solar cells should exhibit a higher conversion efficiency than their n(sup +)p counterparts. This was mainly due to the fact that our p(sup +)n (Cd,S) cell structures consistently showed higher V (sub OC) values than our n(sup +)p (S,Cd) structures. The highest V(sub OC) obtained with the p(sup +)n (Cd,S) cell configuration was 860 mV, as compared to the highest V(sub OC) 840 mV obtained with the n(sup +)p (S,Cd) configuration (AMO, 25 C). In this work, we present the performance results of our most recent thermally diffused cells using the p(sup +)n (Cd,S) structure. We have been able to fabricate cells with V(sub OC) values approaching 880 mV. Our best cell with an unoptimized front contact grid design (GS greater than or equal to 10%) showed a conversion efficiency of 13.4% (AMO, 25 C) without an AR coating layer. The emitter surface was passivated by a -50A P rich oxide. Achievement of such high V(sub OC) values was primarily due to the fabrication of emitter surfaces, having EPD densities as low as 2E2 cm(sup -2) and N(sub a)N(sub d) of about 3E18 cm (sup -3). In addition, our preliminary investigation of p(sup +)n structures seem to suggest that Cd-doped emitter cells are more radiation resistant than Zn-doped emitter cells against both high energy electron and proton irradiation.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: Twelfth Space Photovoltaic Research and Technology Conference (SPRAT 12); p 7
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  • 6
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    Peeled film GaAs solar cells for space power (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Gallium arsenide (GaAs) peeled film solar cells were fabricated, by Organo-Metallic Vapor Phase Epitaxy (OMVPE), incorporating an aluminum arsenide (AlAs) parting layer between the device structure and the GaAs substrate. This layer was selectively removed by etching in dilute hydrofloric (HF) acid to release the epitaxial film. Test devices exhibit high series resistance due to insufficient back contact area. A new design is presented which uses a coverglass superstrate for structural support and incorporates a coplanar back contact design. Devices based on this design should have a specific power approaching 700 W/Kg.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: NASA-TM-103125 , E-5453 , NAS 1.15:103125
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  • 7
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    Sinterless contacts to shallow junction InP solar cells (1992)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: In the past, the achievement of good electrical contact to InP has inevitably been accompanied by mechanical degradation of the InP itself. Most contact systems require heat treatment after metal deposition that results in the dissolution of substantial amounts of InP into the metallization. Devices such as the solar cell, where shallow junctions are the rule, can be severely degraded if the damage to the semiconductor substrate is not precisely controlled. Two contact systems are described that provide low contact resistance to InP solar cells that do not require subjecting the current carrying metallization to a post deposition sintering process. It is shown that these two systems, one nickel based and the other silver based, provide contact resistivity values in the low 10(exp -6) ohm sq cm range, as fabricated, without the need for sintering.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA-TM-105670 , E-7036 , NAS 1.15:105670 , International Conference on Indium Phosphide and Related Materials; Apr 21, 1992 - Apr 24, 1992; Newport, RI; United States
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  • 8
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    A V-grooved GaAs solar cell (1988)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: V-grooved GaAs solar cells promise the benefits of improved optical coupling, higher short-circuit current, and increased tolerance to particle radiation compared to planar cells. A GaAs homojunction cell was fabricated by etching a V-groove pattern into an n epilayer (2.1 x 10 to the 17th power per cu cm) grown by metalorganic chemical vapor deposition (MOCVD) on an n+ substrate (2.8 x 10 to the 18th power per cu cm) and then depositing and MOCVD p epilayer (4.2 x 10 to the 18th power per cu cm). Reflectivity measurements on cells with and without an antireflective coating confirm the expected decrease in reluctance of the microgrooved cell compared to the planar structure. The short circuit current of the V-grooved solar cell was 13 percent higher than that of the planar control.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA-TM-101970 , E-4668 , NAS 1.15:101970 , Photovoltaic Specialists Conference; Sep 26, 1988 - Sep 30, 1988; Las Vegas, NV; United States
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  • 9
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    Non-destructive, ultra-low resistance, thermally stable contacts for use on shallow junction InP solar cells (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Contact formation to InP is plagued by violent metal-semiconductor intermixing that takes place during the contact sintering process. Because of this the InP solar cell cannot be sintered after contact deposition. This results in cell contact resistances that are orders of magnitude higher than those that could be achieved if sintering could be performed in a non-destructive manner. We report here on a truly unique contact system involving Au and Ge, which is easily fabricated, which exhibits extremely low values of contact resistivity, and in which there is virtually no metal-semiconductor interdiffusion, even after extended sintering. We present a description of this contact system and suggest possible mechanisms to explain the observed behavior.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA-TM-106228 , E-7946 , NAS 1.15:106228 , IEEE Photovoltaic Specialists Conference; May 10, 1993 - May 14, 1993; Louisville, KY; United States
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  • 10
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    V-Grooved GaAs Solar Cell (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: V-grooved GaAs solar photovoltaic cells increase optical coupling and greater conversion of light into electricity. Increases both trapping of incident light and lengths of optical paths in cell material. Net effect increases in total absorptivity, tolerance to damage by energetic particles, and short-circuit current. These improvements expected to follow from similar improvements obtained in silicon solar cells.
    Keywords: ELECTRONIC COMPONENTS AND CIRCUITS
    Type: LEW-14954 , NASA Tech Briefs (ISSN 0145-319X); 15; 2; P. 16
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