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Some theoretical aspects of the physics of solar cells
E l l i o t t , J a m e s F., M e i k l e h a m , M r s . V. F. " L a r g e A r e a S o l a r C e l l s " , (1290 60) •
CeSl ~_1.~0 is such a semiconductor, and at present the material is sufticiently optimized to give zT~s of 0.1 and above. Tile study of this semiconductor (n-type) is implemented by the study of a p type semiconductor ThS~.7,_t ~6. Progress to date on these materials is discussed. The measurement of the thermal conductivity of Ce-S at high temperatures, usually very difficult to make, is made by a smMl-area-eontaet teehnique developed at General Atomic.
The utility of photovoliaie solar energy converters to supply large amounts of power (i.e., 0.5-100 kw) will probably be determined by the ability of the industry to supply large area solar cells. Theoretical arguments have been advanced which indicate that polyerystalline silicon prepared by thin film techniques and/or by mechanical deformation of ingots into sheets can be used for cell construction. These two approaches to large area cells are being investigated. Both programs have had promising initial success and the experimental results are discussed. • * *
*
This paper discusses the overall power requirements for some established space missions, and missions that are still being studied and evaluated. Both auxiliary power and propulsive power missions will be considered.
,
• * * H a m i l t o n , R o b e r t C. " R a n g e r S p a c e c r a f t P o w e r S y s tern", (1345-60).
,
Gen-
,
N o t t i n g h a m , W a y n e B. " R e v i e w Thermionics", (1281-60).
of t h e P h y s i c s
of
Heat may be converted directly to electrical power by means of either the vacuum or the plasma thermionie dio~te. The latter holds the greater promise of being valuable for spacepower applications. The input heat is delivered to the emitting surface and the excess heat is radiated from the cooler electron collecting surface. The efficiency of a device depends on the use of a low work-function collector and a minimum of anwanted heat losses. The best gas for the plasma seems to be cesium which serves to eliminate space charge and conduct the electric current across the diode. Some of the basic concepts related to the plasma diode are presented. • • •
Oriented silicon photovoltaie cells provide the basic power source for the Ranger spacecraft. An attitude control system positions the spacecraft so that solar radiation impinges vertieally on the solar cell panels, Primary silverzine batteries provide power during the launch phase, prior to sun aequisition, and during guidance maneuvers when the solar radiation incident on the photovoltaie cells is inadequate to power the Ranger spacecraft, , , ,
with the Development
*
Some of the best materials known at present which are suit able for use in thermoelectric generators are Bi~,Tea and its alloys, PbTe, the I I I - V compounds, MnTe, GeTe, and CeS. The properties of these materials which are important for their use in thermoelectric generators will be discussed. A theoretical maximum ettieieney of 18% would be obtained with these materials working between 30°C and 1030°C, provided that all the design and fabrication problems can be successfully solved.
F i n g e r , H a r o l d B., S c h u l m a n , F r e d . " P o w e r R e q u i r e m e r i t s of t h e N A S A S p a c e P r o g r a m " , ( 1 3 3 3 - 6 0 ) .
H i r s c h , R . L., H o l l a n d , J. W . " P r o b l e m s
*
M i l l e r , 1%. C., U r e , R. W . , J r . " T h e r m o e l e c t r i c erator Materials", (1273-60).
Associated
of a T h e r m i o n i e C o n v e r s i o n
Queisser, Hans
R e a c t o r " , (1338-60).
.l., S h o c k l e y , W i l l i a m .
"Some
Theo-
r e t i c a l A s p e c t s of t.he P h y s i c s of S o l a r C e l l s " , ( 1 2 9 3 -
This paper describes a conceptual design of a 300 kwe thermionic space power reactor with a subsequent discussion of associated development requirements. , , ,
60). Any theoretical treatment of the photovoltaic effect in semiconductors must be based on a thorough understanding of the current-voltage characteristic of a p-n junction. All previous work used the "ideal rectifier equation", a two parameter formula which correctly describes germanium junctions. In order to account for the experimental values of materials which are of interest for solar energy conversion, the two parameters had to be changed enormously from their predieted values in an entirely arbitrary fashion. This clearly shows the inadequacy of the present theory. In the approach proposed here, emphasis is laid on the hole-electron reeoin}fination processes which limit the output voltage of a solar cell. A maximum efficiency may be calculated for the ease of minimmn recombination which is only the radiative one, as required by statistics. Non-radiative recombination prevents reaching this ultimate etticieney. Proposals are made to predict the current-voltage relationship and the e~eieney of a solar cell from first principles with the aid of a theory of recombin',tion processes. , , ,
K e r r , D o u g l a s L. " T h e r m o e l e c t r i c E l e m e n t s in S p a c e P o w e r S y s t e m s " , (1277-60). This paper presents a discussion of some of the eharaeteristies, potentialities, and problems encountered in the design of thermoelectric generators for space applications. One means of classifying the basic configurations possible is according to the means of rejecting heat from the cold junction, i.e. whether it is to be a secondary heat transfer fluid which in turn passes through the radiator or whether the generator waste heat is carried directly to the radiating surfaces by thermal eonduetion from the cold junctions. Presented herein are results of some studies which have been made of the latter ease where the generator is integral with the radiator. TWO types of construetion have been investigated which can be termed the "sandwich" type and the "side fin" type, Estimates of the minimum weight obtainable from each are presented for particular materiMs properties. Comparison of these indicates that a combination of the two types of construction will result in the least weight.
S n y d e r , N . W. " S o l a r C e l l P o w e r S y s t e m s for S p a c e Vehicles", (1309-60). On May 3 and 4, 1960 a symposium was held under the sponsorship of the Advanced Research Projects Agency by the Institute of Defense Analyses. Ten programs involving solar cell power systems for current U. S. space vehicles conducted under govermnent sponsorship were discussed by the project engineers who directed these programs. This paper will highlight amt summarize the results of that symposium for this session, where possible.
K u r n i c k , S. W., F i t z p a t r i c k , R . L., L e a v y , J. F. " H i g h Temperature S e m i c o n d u c t o r s for T h e r m o e l e c t r i c Conversion", (1274-60). At. the high end of the temperature scale (800°K-1600°K), new semiconductors are receiving emphasis in development,
34
CeSl ~_1.~0 is such a semiconductor, and at present the material is sufticiently optimized to give zT~s of 0.1 and above. Tile study of this semiconductor (n-type) is implemented by the study of a p type semiconductor ThS~.7,_t ~6. Progress to date on these materials is discussed. The measurement of the thermal conductivity of Ce-S at high temperatures, usually very difficult to make, is made by a smMl-area-eontaet teehnique developed at General Atomic.
The utility of photovoliaie solar energy converters to supply large amounts of power (i.e., 0.5-100 kw) will probably be determined by the ability of the industry to supply large area solar cells. Theoretical arguments have been advanced which indicate that polyerystalline silicon prepared by thin film techniques and/or by mechanical deformation of ingots into sheets can be used for cell construction. These two approaches to large area cells are being investigated. Both programs have had promising initial success and the experimental results are discussed. • * *
*
This paper discusses the overall power requirements for some established space missions, and missions that are still being studied and evaluated. Both auxiliary power and propulsive power missions will be considered.
,
• * * H a m i l t o n , R o b e r t C. " R a n g e r S p a c e c r a f t P o w e r S y s tern", (1345-60).
,
Gen-
,
N o t t i n g h a m , W a y n e B. " R e v i e w Thermionics", (1281-60).
of t h e P h y s i c s
of
Heat may be converted directly to electrical power by means of either the vacuum or the plasma thermionie dio~te. The latter holds the greater promise of being valuable for spacepower applications. The input heat is delivered to the emitting surface and the excess heat is radiated from the cooler electron collecting surface. The efficiency of a device depends on the use of a low work-function collector and a minimum of anwanted heat losses. The best gas for the plasma seems to be cesium which serves to eliminate space charge and conduct the electric current across the diode. Some of the basic concepts related to the plasma diode are presented. • • •
Oriented silicon photovoltaie cells provide the basic power source for the Ranger spacecraft. An attitude control system positions the spacecraft so that solar radiation impinges vertieally on the solar cell panels, Primary silverzine batteries provide power during the launch phase, prior to sun aequisition, and during guidance maneuvers when the solar radiation incident on the photovoltaie cells is inadequate to power the Ranger spacecraft, , , ,
with the Development
*
Some of the best materials known at present which are suit able for use in thermoelectric generators are Bi~,Tea and its alloys, PbTe, the I I I - V compounds, MnTe, GeTe, and CeS. The properties of these materials which are important for their use in thermoelectric generators will be discussed. A theoretical maximum ettieieney of 18% would be obtained with these materials working between 30°C and 1030°C, provided that all the design and fabrication problems can be successfully solved.
F i n g e r , H a r o l d B., S c h u l m a n , F r e d . " P o w e r R e q u i r e m e r i t s of t h e N A S A S p a c e P r o g r a m " , ( 1 3 3 3 - 6 0 ) .
H i r s c h , R . L., H o l l a n d , J. W . " P r o b l e m s
*
M i l l e r , 1%. C., U r e , R. W . , J r . " T h e r m o e l e c t r i c erator Materials", (1273-60).
Associated
of a T h e r m i o n i e C o n v e r s i o n
Queisser, Hans
R e a c t o r " , (1338-60).
.l., S h o c k l e y , W i l l i a m .
"Some
Theo-
r e t i c a l A s p e c t s of t.he P h y s i c s of S o l a r C e l l s " , ( 1 2 9 3 -
This paper describes a conceptual design of a 300 kwe thermionic space power reactor with a subsequent discussion of associated development requirements. , , ,
60). Any theoretical treatment of the photovoltaic effect in semiconductors must be based on a thorough understanding of the current-voltage characteristic of a p-n junction. All previous work used the "ideal rectifier equation", a two parameter formula which correctly describes germanium junctions. In order to account for the experimental values of materials which are of interest for solar energy conversion, the two parameters had to be changed enormously from their predieted values in an entirely arbitrary fashion. This clearly shows the inadequacy of the present theory. In the approach proposed here, emphasis is laid on the hole-electron reeoin}fination processes which limit the output voltage of a solar cell. A maximum efficiency may be calculated for the ease of minimmn recombination which is only the radiative one, as required by statistics. Non-radiative recombination prevents reaching this ultimate etticieney. Proposals are made to predict the current-voltage relationship and the e~eieney of a solar cell from first principles with the aid of a theory of recombin',tion processes. , , ,
K e r r , D o u g l a s L. " T h e r m o e l e c t r i c E l e m e n t s in S p a c e P o w e r S y s t e m s " , (1277-60). This paper presents a discussion of some of the eharaeteristies, potentialities, and problems encountered in the design of thermoelectric generators for space applications. One means of classifying the basic configurations possible is according to the means of rejecting heat from the cold junction, i.e. whether it is to be a secondary heat transfer fluid which in turn passes through the radiator or whether the generator waste heat is carried directly to the radiating surfaces by thermal eonduetion from the cold junctions. Presented herein are results of some studies which have been made of the latter ease where the generator is integral with the radiator. TWO types of construetion have been investigated which can be termed the "sandwich" type and the "side fin" type, Estimates of the minimum weight obtainable from each are presented for particular materiMs properties. Comparison of these indicates that a combination of the two types of construction will result in the least weight.
S n y d e r , N . W. " S o l a r C e l l P o w e r S y s t e m s for S p a c e Vehicles", (1309-60). On May 3 and 4, 1960 a symposium was held under the sponsorship of the Advanced Research Projects Agency by the Institute of Defense Analyses. Ten programs involving solar cell power systems for current U. S. space vehicles conducted under govermnent sponsorship were discussed by the project engineers who directed these programs. This paper will highlight amt summarize the results of that symposium for this session, where possible.
K u r n i c k , S. W., F i t z p a t r i c k , R . L., L e a v y , J. F. " H i g h Temperature S e m i c o n d u c t o r s for T h e r m o e l e c t r i c Conversion", (1274-60). At. the high end of the temperature scale (800°K-1600°K), new semiconductors are receiving emphasis in development,
34