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Silicio nanocristallino: potenzialita e promesse L. Pavesi L. Pavesi 28-11-10 Nanoscience Laboratory Oleksiy Anopchenko Minhaz Hossein(*) Stefano Prezioso (*) Zhizhong Yuan (Ryan) (*) Fabrizio Sgrignuoli Alessandro Marconi APP FBK

slide-1
SLIDE 1
  • L. Pavesi

28-11-10

Silicio nanocristallino: potenzialita’ e promesse

  • L. Pavesi
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SLIDE 2
  • L. Pavesi

28-11-10

Nanoscience Laboratory Oleksiy Anopchenko Minhaz Hossein(*) Stefano Prezioso (*) Zhizhong Yuan (Ryan) (*) Fabrizio Sgrignuoli Alessandro Marconi APP FBK Georg Pucker Yoann Jestin MTLab FBK Pierluigi Bellutti Lorenza Ferrario

slide-3
SLIDE 3
  • L. Pavesi

28-11-10

Outline

  • Silicon photovoltaics: the continuous

evolution

  • Nanocrystalline silicon as a tool to

implement third generation PV

  • Three examples of our research

– Downshifter – Cell with internal gain – Towards tandem cells

  • Conclusions
slide-4
SLIDE 4
  • L. Pavesi

28-11-10

Outline

  • Silicon photovoltaics: the continuous

evolution

  • Nanocrystalline silicon as a tool to

implement third generation PV

  • Three examples of our research

– Downshifter – Cell with internal gain – Towards tandem cells

  • Conclusions
slide-5
SLIDE 5
  • L. Pavesi

28-11-10 “Courtesy of the National Renewable Energy Laboratory, Golden, Colorado.

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SLIDE 6
  • L. Pavesi

28-11-10

Solar Cells 2010 Market Share Estimate

0% 10% 20% 30% 40% 50% Type Market Share

Solar Cells Market Estimate

SEMI PV Group March 2009 from source Yole Development

>90%

slide-7
SLIDE 7
  • L. Pavesi

28-11-10

Various PV generations

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SLIDE 8
  • L. Pavesi

28-11-10

First Generation Solar Cells

  • Single crystal silicon wafers
  • Dominant in the commercial production of solar cells
  • Consist of a large-area, single layer p-n junction
  • Best crystalline Si solar cell efficiency: ~ 25%
  • Advantages

– Broad spectral absorption range – High carrier mobility

  • Disadvantages

– Most of photon energy is wasted as heat – Require expensive manufacturing technologies

8

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SLIDE 9
  • L. Pavesi

28-11-10

Various PV generations

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SLIDE 10
  • L. Pavesi

28-11-10

Second Generation Solar Cells

  • Thin-film Technologies

– Amorphous silicon – Polycrystalline silicon

– Cadmium Telluride (CdTe)

  • Best large area Si-based solar cell efficiency: ~ 22%
  • Advantages

– Low material cost – Reduced mass

  • Disadvantages

– Toxic material (Cd), – Scarce material (Te)

10

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SLIDE 11
  • L. Pavesi

28-11-10

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SLIDE 12
  • L. Pavesi

28-11-10

The Main Losses in Solar Cells

qV

Lattice thermalisation loss

Junction loss Recombination loss Contact loss Sub bandgap loss

Energy

 Sub bandgap and Lattice thermalisation losses acount for more than

50% of the total loss

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SLIDE 13
  • L. Pavesi

28-11-10

Third Generation Solar Cells

  • Solar cells which use concepts that allow for a more

efficient utilization of the sunlight than FG and SG solar cells

13

Photon electron energy conversion 32.9% Unabsorbed energy loss 18.7% Heat loss 46.8% Other losses 1.6%

slide-14
SLIDE 14
  • L. Pavesi

28-11-10

Various PV generations

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SLIDE 15
  • L. Pavesi

28-11-10

Third Generation Solar Cells

  • Solar cells which use concepts that allow for a more

efficient utilization of the sunlight than FG and SG solar cells

  • The biggest challenge is reducing the cost/watt of

delivered solar electricity

  • Third generation solar cells pursue

– More efficiency – More abundant materials – Non-toxic material – Durability

15

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SLIDE 16
  • L. Pavesi

28-11-10

Third Generation Solar Cells

  • Solar cells which use concepts that allow for a more

efficient utilization of the sunlight than FG and SG solar cells

  • The biggest challenge is reducing the cost/watt of

delivered solar electricity

  • Third generation solar cells pursue

– More efficiency – More abundant materials – Non-toxic material – Durability

16

slide-17
SLIDE 17
  • L. Pavesi

28-11-10

Band gap engineering using quantum confinement effect Multiple Exciton Generation Hot Carrier Solar Cell Up Conversion Down Conversion Tandem Cells

Third Generation Solar Cells

"Energy & Nano" - Top Master Symposium in Nanoscience 2009

17

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SLIDE 18
  • L. Pavesi

28-11-10

Band gap engineering using quantum confinement effects Multiple Exciton Generation Hot Carrier Solar Cell Up Conversion Down Conversion Tandem Cells

Third Generation Solar Cells

"Energy & Nano" - Top Master Symposium in Nanoscience 2009

18

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SLIDE 19
  • L. Pavesi

28-11-10

Outline

  • Silicon photovoltaics: the continuous

evolution

  • Nanocrystalline silicon as a tool to

implement third generation PV

  • Three examples of our research

– Downshifter – Cell with internal gain – Towards tandem cells

  • Conclusions
slide-20
SLIDE 20
  • L. Pavesi

28-11-10

Silicon nanocrystals

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SLIDE 21
  • L. Pavesi

28-11-10

Silicon quantum dots

Increase the emission energy

2

2 2

Si gap gap

E E m L          

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SLIDE 22
  • L. Pavesi

28-11-10

Silicon quantum dots

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SLIDE 23
  • L. Pavesi

28-11-10

Properties of Si-nc

1. Abundant and nontoxic 2. CMOS fabrication compatible 3. Band gap adjustable and higher than that of Si

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SLIDE 24
  • L. Pavesi

28-11-10

Optical properties of Si-nc

550 650 750 850 950

PDS-1 PDS-2

PL intensity (a.u.) Wavelength (nm) (c) (a) (b)

400 500 600 700

25 50

Absorbance (%) 2E

Si g

1 10

PL intensity (a.u.)

Monitoring PL band at 800 nm

Stokes shift between absorption and emission

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SLIDE 25
  • L. Pavesi

28-11-10

Significant size dispersion

  • F. Iacona et al. CNR Catania
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SLIDE 26
  • L. Pavesi

28-11-10

Reduce the size dispersion

  • M. Zacharias et al. MPI Halle
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SLIDE 27
  • L. Pavesi

28-11-10

Current?

  • 1. reduce IDD
  • 2. reduce BH
  • 3. improve overlapping of wave function of Si-nc

SiO2

Si-nc

p-Si n-Si

+

  • Electron

Hole

F-N tunneling Direct tunneling BH

IDD

BH: Barrier height IDD: Inter-dot distance

n-Si p-Si D 1.Reduce D 2.Improve

  • verlapping of

wave function

  • f Si-nc
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SLIDE 28
  • L. Pavesi

28-11-10

nc-Si/SiO2 Multilayer LED

  • Confined growth of nanocrystals
  • Better oxide quality
  • Control over the oxide thickness
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SLIDE 29
  • L. Pavesi

28-11-10 Fowler-Nordheim Tunneling Direct Tunneling Position

  • Less destructive
  • More efficient

>3V <3V Energy Position Oxide nc-Si

nc-Si/SiO2 Multilayer LED

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SLIDE 30
  • L. Pavesi

28-11-10

nc-Si/SiO2 Multilayer LED

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SLIDE 31
  • L. Pavesi

28-11-10

Single layer vs Multilayer LED

1 2 3 1E-10 1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0,01

Current Density (A/cm

2)

Electric Field (MV/cm)

Single layer = large current Multilayer= large field Larger Electric Field to achieve the same Current Density, i.e. reduced the leakage current

Single layer Multilayer

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SLIDE 32
  • L. Pavesi

28-11-10

Single layer vs Multilayer LED

Increase of EL due to more effective injection into the Si-nc

32

1 2 3

Electric Field (MV/cm)

10 10

1

10

2

10

3

10

4

10

5

Elettroluminescence density (a.u.)

Single layer Multilayer Same injected current

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SLIDE 33
  • L. Pavesi

28-11-10

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SLIDE 34
  • L. Pavesi

28-11-10

10

  • 3

10

  • 2

10

  • 1

1 10

1

0.01 0.1 1

(2 nm SiO2 / 3 nm SRO) Graded energy gap (2 nm SiO2 / 4 nm SRO)

Optical power density (W / cm

2)

Current density (mA / cm

2)

10

  • 3

10

  • 2

10

  • 1

1

0.0 0.1 0.2 Power efficiency (%) Current density (mA / cm

2)

Active Si-NC n-type poly- silicon 100 nm p-type silicon wafer +

  • pHotonics ELectronics functional

Integration on CMOS

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SLIDE 35
  • L. Pavesi

28-11-10

Key issues: Control the current

  • Different Matrixes: different barrier heights

Bulk band alignments between crystallinc silicon and its carbide, nitride and oxide.

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SLIDE 36
  • L. Pavesi

28-11-10

Wave function

  • overlap of the wave function can enhance the tunneling between

adjacent Si-ncs.

*

/ 1952 . m E m nm Ld   

Si Si Si Si Si Si

SiO2 Si3N4 SiC The wave function of an electron confined to a spherical dot penetrates into the surrounding materials, decaying approximately as exp(-r/Ld)/r, where r is the distance from the centre of the dot.

Ld, decay length.

Matrix SiO2 Si3N4 SiC ∆E(Si-Matrix) 3.2 eV 1.9 eV 0.5 eV m0 0.86 0.05-0.13 0.24

Inter-dot distance for significant wavefunction overlap: 1-2 nm for SiO2 and 4 nm fro SiC

Eun-Chel Cho, et al., Advances in Optoelectronics. 2007, 1-11

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SLIDE 37
  • L. Pavesi

28-11-10

Photoresponsivity-superlattice

400 500 600 700 800 1E-4 1E-3 0.01 Q2-SRO/SiO2=3/1 Q7-SRN/SiO2=3/1 Q8-SRO/Si3N4=3/1 Q9-SRN/Si3N4=3/1

Photoresponsivity (A/W) Wavelength (nm)

slide-38
SLIDE 38
  • L. Pavesi

28-11-10

Band gap engineering using quantum confinement effects Multiple Exciton Generation Hot Carrier Solar Cell Up Conversion Down Conversion Tandem Cells

Third Generation Solar Cells

"Energy & Nano" - Top Master Symposium in Nanoscience 2009

38

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SLIDE 39
  • L. Pavesi

28-11-10

  • A. J. Nozik
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SLIDE 40
  • L. Pavesi

28-11-10

Band gap engineering using quantum confinement effects Multiple Exciton Generation Hot Carrier Solar Cell Up Conversion Down Conversion Tandem Cells

Third Generation Solar Cells

"Energy & Nano" - Top Master Symposium in Nanoscience 2009

40

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SLIDE 41
  • L. Pavesi

28-11-10

Hot carrier solar cell-to increase Voc

  • G. Conibeer, et al., Thin Solid Films,511-512, 654 (2006)
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SLIDE 42
  • L. Pavesi

28-11-10

Band gap engineering using quantum confinement effects Multiple Exciton Generation Hot Carrier Solar Cell Up Conversion Down Conversion Tandem Cells

Third Generation Solar Cells

"Energy & Nano" - Top Master Symposium in Nanoscience 2009

42

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SLIDE 43
  • L. Pavesi

28-11-10

Mechanism of tandem solar cell

Sunlight Solar cell Decreasing band gap

Cell stacking

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SLIDE 44
  • L. Pavesi

28-11-10

  • All silicon tandem solar cell- to increase current

Schematic of three-cell and two-cell tandem solar cell with an Si bottom cell.

Eun-Chel Cho, et al., Advances in Optoelectronics. 2007, 1-11

slide-45
SLIDE 45
  • L. Pavesi

28-11-10

Outline

  • Silicon photovoltaics: the continuous

evolution

  • Nanocrystalline silicon as a tool to

implement third generation PV

  • Three examples of our research

– Downshifter – Cell with internal gain – Towards tandem cells

  • Conclusions
slide-46
SLIDE 46
  • L. Pavesi

28-11-10

Improved photovoltaic efficiency by applying novel effects at the limits of light-matter interaction

Ryan, Anopchenko, Marconi – APP FBK

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SLIDE 47
  • L. Pavesi

28-11-10

Improved photovoltaic efficiency by applying novel effects at the limits of light-matter interaction

Silicon nanocrystals Ryan, Anopchenko, Marconi – APP FBK

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SLIDE 48
  • L. Pavesi

28-11-10

300 400 500 600 700 800 900 0,1 1

Absorbance Wavelength (nm)

1 2

Luminescence (a.u.)

> 60% Quantum Efficiency > 60%

  • R. J. Walters et al. Phys. Rev. B, 73, 132302 (2006).
slide-49
SLIDE 49
  • L. Pavesi

28-11-10

Improved photovoltaic efficiency by applying novel effects at the limits of light-matter interaction

Ryan, Anopchenko, Marconi – APP FBK

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SLIDE 50
  • L. Pavesi

28-11-10

400 500 600 700 0.0 0.2 0.4 0.6 0.8 1.0 Optical function Wavelength (nm) TSRO RSRO ASRO

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SLIDE 51
  • L. Pavesi

28-11-10

400 500 600 700 0.0 0.2 0.4 0.6 0.8 1.0 Optical function Wavelength (nm) TSRO RSRO ASRO 0.0 0.1 0.2 0.3 Photoresponsivity (A/W) PR PRARC (b) PDS-2

PR measured photoresponsivity PRARC calculated photoresponsivity with a passive layer

PL+ARC

PR

ARC

PR

ARC

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SLIDE 52
  • L. Pavesi

28-11-10

A maximum enhancement of the internal quantum efficiency of 14%

400 500 600 700 0.0 0.2 0.4 0.6 0.8 1.0 Optical function Wavelength (nm) TSRO RSRO ASRO 0.0 0.1 0.2 0.3 Photoresponsivity (A/W) Internal quantum efficiency enhancement PR PRARC INT (b) PDS-2

slide-53
SLIDE 53
  • L. Pavesi

28-11-10

Outline

  • Silicon photovoltaics: the continuous

evolution

  • Nanocrystalline silicon as a tool to

implement third generation PV

  • Three examples of our research

– Downshifter – Cell with internal gain – Towards tandem cells

  • Conclusions
slide-54
SLIDE 54
  • L. Pavesi

28-11-10

Improve photovoltaic efficiency by applying novel effects at the limits of light-matter interaction

Secondary carrier generation

Ryan, Anopchenko, Marconi – APP FBK - Minhaz

slide-55
SLIDE 55
  • L. Pavesi

28-11-10

Cross section of the device

Device area = 320 m X 320 m

Al (1%Si) 500 nm P-type Si substrate Si-rich Oxide 50 nm SiO2 (TEOS) 120 nm LPCVD Si3N4 50 nm n-type Poly-Si 30 nm Al (1%Si) 500 nm LOCOS 500 nm LOCOS 500 nm Al (1%Si) 500 nm Ryan, Anopchenko, Marconi – APP FBK - Minhaz

slide-56
SLIDE 56
  • L. Pavesi

28-11-10

Cross section of the device

Device area = 320 m X 320 m

Al (1%Si) 500 nm P-type Si substrate Si-rich Oxide 50 nm SiO2 (TEOS) 120 nm LPCVD Si3N4 50 nm n-type Poly-Si 30 nm Al (1%Si) 500 nm LOCOS 500 nm LOCOS 500 nm Al (1%Si) 500 nm absorption Ryan, Anopchenko, Marconi – APP FBK - Minhaz

slide-57
SLIDE 57
  • L. Pavesi

28-11-10

Cross section of the device

Device area = 320 m X 320 m

Al (1%Si) 500 nm P-type Si substrate Si-rich Oxide 50 nm SiO2 (TEOS) 120 nm LPCVD Si3N4 50 nm n-type Poly-Si 30 nm Al (1%Si) 500 nm LOCOS 500 nm LOCOS 500 nm Al (1%Si) 500 nm absorption multiplication Ryan, Anopchenko, Marconi – APP FBK - Minhaz

slide-58
SLIDE 58
  • L. Pavesi

28-11-10

Spectral Response for 10: small nanocrystals

400 600 800 1000 0.0 0.5 1.0 1.5 2.0 2.5

Responsivity (mA / W) Wavelength (nm)

1400 1500 1600 0.5 1.0 1.5 2.0 2.5

Responsivity (nA / W) Wavelength (nm)

Below the band gap of both Si and nc-Si Nitrogen related states

* at the reverse bias of 5 V

slide-59
SLIDE 59
  • L. Pavesi

28-11-10

  • 5
  • 4
  • 3
  • 2
  • 1

0.2 0.4 0.6 0.8 1.0

Current (nA) Reverse bias voltage (V)

dark 1310 nm, 6 mW

IR absorption in 10: small nanocrystals

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SLIDE 60
  • L. Pavesi

28-11-10

  • 5
  • 4
  • 3
  • 2
  • 1
  • 2.0
  • 1.5
  • 1.0
  • 0.5

0.0 0.5 1.0

Photo-current (IL - ID) (mA) Applied Bias(V)

> 1200 nm

IR response in 3N

slide-61
SLIDE 61
  • L. Pavesi

28-11-10

  • 5
  • 4
  • 3
  • 2
  • 1
  • 2.0
  • 1.5
  • 1.0
  • 0.5

0.0 0.5 1.0 Voc= 500 mV

Photo-current (IL - ID) (mA) Applied Bias(V)

633 nm 488 nm > 1200 nm

IR response in 3N

slide-62
SLIDE 62
  • L. Pavesi

28-11-10

  • 5
  • 4
  • 3
  • 2
  • 1
  • 2.0
  • 1.5
  • 1.0
  • 0.5

0.0 0.5 1.0 Voc= 500 mV

Photo-current (IL - ID) (mA) Applied Bias(V)

633 nm + 1200 nm 488 nm + 1200 nm > 1200 nm

IR response in 3N

slide-63
SLIDE 63
  • L. Pavesi

28-11-10

  • 5
  • 4
  • 3
  • 2
  • 1
  • 2.0
  • 1.5
  • 1.0
  • 0.5

0.0 0.5 1.0 Voc= 500 mV

Photo-current (IL - ID) (mA) Applied Bias(V)

633 nm + 1200 nm 488 nm + 1200 nm > 1200 nm

IR response in 3N

10 %

slide-64
SLIDE 64
  • L. Pavesi

28-11-10

Solar cell with an internal gain mechanism

Secondary carrier generation Ryan, Anopchenko, Marconi – APP FBK - Minhaz

slide-65
SLIDE 65
  • L. Pavesi

28-11-10

Outline

  • Silicon photovoltaics: the continuous

evolution

  • Nanocrystalline silicon as a tool to

implement third generation PV

  • Three examples of our research

– Downshifter – Cell with internal gain – Towards tandem cells

  • Conclusions
slide-66
SLIDE 66
  • L. Pavesi

28-11-10

Objective:

  • Use of a quartz wafer to eliminate the

influence of the Si substrate and to study photovoltaic properties of the single QD sub-cells in the tandem stack

slide-67
SLIDE 67
  • L. Pavesi

28-11-10

The structure of the device

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SLIDE 68
  • L. Pavesi

28-11-10

Experimental

No. Active layer Period of multi-layer Layer thickness Q1 SRO/SiO2 5 2 nm + 1 nm Q2 SRO/SiO2 5 3 nm + 1 nm Q3 SRO 20 nm Q5

-Si/SiO2

5 3 nm + 1 nm Q7 SRN/SiO2 5 3 nm + 1 nm Q8 SRO/Si3N4 5 3 nm + 1 nm Q9 SRN/Si3N4 5 3 nm + 1 nm

slide-69
SLIDE 69
  • L. Pavesi

28-11-10

  • 1.0
  • 0.8
  • 0.6
  • 0.4
  • 0.2

0.0 0.2 0.4 1E-12 1E-11 1E-10 1E-9 1E-8 1E-7 1E-6 1E-5 1E-4

ICurrent (A)I Voltage (V)

SRO/SiO2 SRO a-Si/SiO2

I-V curves measured in dark

slide-70
SLIDE 70
  • L. Pavesi

28-11-10

Photoresponsivity-1

400 500 600 700 800 10

  • 5

10

  • 4

10

  • 3

Q1(SRO/SiO2=2nm/1nm) Q2(SRO/SiO2=3nm/1nm) Q3(SRO) Q5(-Si/SiO2=3nm/1nm) Q7(SRN/SiO2=3nm/1nm)

Photoresponsivity (A/W) Wavelength (nm)

Q5

  • 1. Q5 has the highest PR.
  • 2. Q5 has comparatively higher PR than the SRO single layer for wavelength

between 400 and 470 nm (due to enhanced absorption of nanostructures).

slide-71
SLIDE 71
  • L. Pavesi

28-11-10

a-Si/SiO2 shows the best PV effect

0.00 0.05 0.10 0.15 0.20 1 2 3 4 5 6 7

Current (A) Voltage (V)

3.4 A 120 mV FF: 30.2 Isc: 6 ± 1 A Voc: 220 ± 1 mV Pmax: 40.8 W/cm

2

Rserial = 23.6 kΩ Rshunt = 51.2 kΩ Rserial = 6.41 kΩ Rshunt = 54.1 kΩ Lambert W function Conversion efficiency 0.41 %

slide-72
SLIDE 72
  • L. Pavesi

28-11-10

Outline

  • Silicon photovoltaics: the continuous

evolution

  • Nanocrystalline silicon as a tool to

implement third generation PV

  • Three examples of our research

– Downshifter – Cell with internal gain – Towards tandem cells

  • Conclusions
slide-73
SLIDE 73
  • L. Pavesi

28-11-10

Requirements for high efficiency nanocrystalline solar cell

  • High silicon nanocrystal density

– Large conductivity (interdot coupling) – Large absorption (large optical density)

  • Low energy barrier dielectrics

– Large conductivity

  • More photon management

– Dielectric constant

slide-74
SLIDE 74
  • L. Pavesi

28-11-10

Conclusions

slide-75
SLIDE 75
  • L. Pavesi

28-11-10

Acknowledgments

  • EC: Helios, LIMA
  • HCSC project and OptoI
  • ITPAR and CENTER FOR GREEN ENERGY

AND SENSOR SYSTEMS – BESU - India