Bifacial Si Cells for Space Applications

Fabricated Using Combined

Ion Implantation –Thermal Diffusion

Technology

Bifacial Si Cells for Space Applications

Fabricated Using Combined

Ion Implantation –Thermal Diffusion

Technology

G. Grigorieva, M. Kagan, K. Zviagina,

KVANT, Moscow , Russia,

L. Kreinin, N. Bordin, N. Eisenberg

Jerusalem College of Technology, Jerusalem, Israel

G. Grigorieva, M. Kagan, K. Zviagina,

KVANT, Moscow , Russia,

L. Kreinin, N. Bordin, N. Eisenberg

Jerusalem College of Technology, Jerusalem, Israel

OUTLINE

1. Space application of bifacial solar cells

2. n+-p-p+ bifacial cells produced by combined thermal

diffusion - ion implantation technology diffusion - ion implantation technology

3. Production and research achievements useful for

fabrication of terrestrial bifacial solar cell

BIFACIAL SOLAR ARRAYS IN SPACE

Bifacial Si solar arrays were mounted on spacecrafts

"Zarya" and "Zvezda" of Russian segment of the ISS.

A BIFACIAL ARRAY ON THE SALUT-5 SPACE STATION AT 350 KM ALTITUDE GENERATED ON AVERAGE~ 17% MORE

POWER THAN A CONVENTIONAL PANEL.

Simulation and space tests of bifacial solar cells in space

were first undertaken in the early 70-s

Power generation enhancement achieved using bifacial instead of regular Si solar cells

(flight data)

Power

generation

gain, %

Orbit

type

Launch

year

Spacecraft name

17 – 34LEO1974Salut-3

17-45LEO1976Salut-5 17-45LEO1976Salut-5

12LEO1987Kosmos-1870

10-20LEO1991Almaz

Reliability

improved

GEO1993Electro

10-20LEO1998Zarya (ISS section)

10-20LEO2000Zvezda (ISS section)

Total Equivalent Efficiency of

Bifacial Si Solar Cell with AM0

Front and Back Efficiencies 18 and 13.5 %

Feathered solar array

to minimize drag

One-axis sun

tracking

Full two-axis sun

tracking

Altitude of circular orbit, km

1000 6002001000 6002001000600200

Equivalent efficiency

25.024.624.320.320.521.220.521.021.5

Bifacial solar cell with thermally doped

emitter and implanted back p+ layer

Front and back photovoltaic

parameters of a Si bifacial solar cell

Jsc, mA/cm2 Voc, mV FF ηηηη, % Front 38.1 637 0.78 19 Back 31.6 632 0.79 16

B profiles before and after annealing

Concentration of electro active acceptors in Si

implanted by 30 keV B ions

Schematic of a bifacial n+-p-p+ solar

cell with B implanted p+ layer

Seff1 and Ln2 were calculated based on back IQE data.

IQE was analytically described using a model with

a stepwise defect distribution in the base region

Effect of Si resistivity

Back internal quantum efficiency for solar cells fabricated using FZ Si of different resistivity. Implantation dose was

5.6•1015 cm -2. Measurements under sunlight bias.Seff1 = 1050 cm/s, L2 = 11 µµµµm in 1 ΩΩΩΩ.cm cell

no measureable effect in 20 ΩΩΩΩ.cm cell

Effect of injection level

Back internal quantum efficiency for solar cells fabricated

using 20 Ω.cm FZ Si. Implantation dose was 1.25•1016 cm-2.

Seff1 = 1070 cm/s, L2 = 11 µm when no light bias, no observable effect when sunlight biased

Multi crystalline solar cells

Back internal quantum efficiency for solar cells fabricated using multi crystalline 1 Ω.cm Si. Implantation dose was

1.25•1016 cm-2

Seff1 = 8100 and 2500 cm/s, L2 = 5.5 and 1.7 µµµµm without and with sunlight bias, respectively

RECOMBINATION PARAMETERS OF DEFECT

LAYERS ADJOINING p+ LAYER FROM BASE

side (of ~0.5 µm thickness)

Effective surface

recombination

velocity, cm/s

Diffusion length

in defect layer,

µµµµm

Irradiance,

mW/cm2

Si

resistivity,

ΩΩΩΩ.cm

Implantation

dose, cm-2

Sample #

9801210013.1. 1015F-25-3 9801210013.1. 1015F-25-3

106011.210016.3. 1015F-16-1

108011~0.1

201.25. 101620-11-3 1.1-100

81001.7~0.1

11.25. 1016Poly 2-12-4 25005.5100

SUMMARY

• Bifacial Si solar cells are able to supply 15-45 % more energy than regular Si cells on LEO space craft.

• The advantages of bifacial Si solar cell are expressed in equivalent efficiency achieving 25 %.

• Technology of space bifacial cells based on the combination of thermal P diffusion for n+ layer doping and B ion implantation thermal P diffusion for n+ layer doping and B ion implantation for p+ layer doping is very promising for fabrication of terrestrial bifacial cells.

• Formation of the defect layer adjoined to BSF should be prevented in fabrication process.

• Ion dose, Si parameters (resistivity, single or multi crystalline) as well as carrier injection level during the measurements are factors affecting the influence of such a layer.