introduction photonics for energy · semiconductor physics solar cells electrical parameters cigs...

Winter School onPhotonics for Energy

Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History

Semiconductor physics

Solar cells

Electrical parameters

CIGS solar cells

Multijunction solar cells

Other solar cells

Current marketdevelopment

The future

Solid state solar cells.1


Solid state solar cells

Uwe ZimmermannSolid State Electronics

Uppsala university


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Outline.

This lecture shall give answers to the following questions:

• Why solar cells?• What is a solid state solar cell?• What was the history of the solar cell?• What is the current state of solar cells?• What are the important parameters of a solar cell?• What is limiting the conversion efficiency?• What can we expect from current solar cell technologies?• How sustainable are solar cells?• Where are we going from here?


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


A glimpse into the future.

Shell energy scenarios to 2050

• Overall energy consumption of the world is expected tocontinue growing.

• Future energy production must be affordable andsustainable.


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Grid Parity.

McKinsey Quarterly, June 2008


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


PV potential in Europe.


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Direct and diffuse sunlight.

direct

circumsolar diffuse

isotropic diffuse from sky

diffuse from horizon

reflektion

reflected

The global irradiation consists of• direct sunlight• diffuse sunlight• reflected sunlight


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Direct light in Africa.

• more than 80 % of the insolation in Africa come from directsunlight


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Diffuse light in Europe.

• Up to 64 % of the insolation in northern Europe come fromdiffuse sunlight.

• Diffuse sunlight can not be focused or concentrated.


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Advantages of solar cells.

• Solar cells have no moving parts.• Solar cells are emission-free during operation.• Solar cells are silent.• Solar cell installations can be compact.• Solar cell installations are scalable.


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Some history.

1839 Alexandre-Edmond Becquerel (father of Henry B.)discovers the photovoltaic effect

1876 the selenium solid-state cell is invented1954 the modern silicon solar cell is invented at Bell Labs

with 6 % efficiency1958 the first silicon solar cell in space1970:s the oil crisis leads to an increased interest in solar

cells for terrestial use1980 first thin film solar cell with > 10 % efficiency2001 cumulative (1954-2001) worldwide installed

PV power capacity reaches 1 GWp2003 cumulative worldwide installed PV power

capacity reaches 2 GWp2008 Spain installs about 2.6 GWp new PV capacity2009 Germany installs about 3 GWp new PV capacity


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


The first modern solar cell.

• The silicon solar cell was invented by D. Chapin, C. Fullerand G. Pearson at Bell Labs.

• The transistor had been invented at the same location 7years earlier.

• 1958 the first commercial solar-cell driven transistor radiowas available.

• Also in 1958 the first solar cells were used in space.• . . . then for about 30 years not much happened. . . or did it?


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


The first solar-cell satellite.

http://www.nasa.gov

• Vanguard I, launched 1958-03-17 from Cape Canaveral.• The fourth artificial satellite, second US satellite.• 1.47 kg aluminum sphere 16.5 cm in diameter.• 10 mW, 108 MHz mercury-battery powered transmitter.• 5 mW, 108.03 MHz transmitter powered by six solar cells.• The batteries stopped working in June 1958,

the solar cells in May 1964.

http://www.nasa.gov


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Teaching in the early years.

• In the early 1960’s Bell Labs introduced a series ofexperimental kits.

• Target audience were highschool teachers and theirclasses.

• Bell Systems Science Experiment No. 2 containseverything to make your own silicon solar cells.


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


The solar cell.

• Light can be understood as a flow of photons.• Photons are absorbed in the solar cell.• Electron-hole-pairs are created – one per photon.• Charge carriers drift/diffuse to the contacts.• An electrical current can leave the solar cell.


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Photon absorption.

valence band

conduction band

Eg

• photons with E < Eg are not absorbed• photons with E ≥ Eg are absorbed

• an electron-hole pair is created• photons with E Eg are absorbed

• additional energy is absorbed by the crystal lattice


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Light absorption in semiconductors.

0.0

1.0

2.0

3.0

4.0

5.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

2500 1500 1000 800 600 400ph

oton

flux

[1x1

021 m

−2 s

−1 e

V−

1 ]

photon energy [eV]

wave length [nm]

AM 1.5

black body 5800K

Eg

absorption

Eg

absorption

Eg

absorption

• A semiconductor with a bandgap Eg can absorb photons with E > Eg .

• A lower bandgap means there are more photons which can be absorbed:⇒ more electron-hole-pairs⇒ higher current⇒ but lower voltage (V ≈ Eg/2q)

• A wider bandgap means there are fewer photons which can be absorbed⇒ fewer electron-hole-pairs⇒ lower current⇒ but higher voltage can be achieved


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Typical semiconductors.

0.0

1.0

2.0

3.0

4.0

5.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

2500 1500 1000 800 600 400ph

oton

flux

[1x1

021 m

−2 s

−1 e

V−

1 ]

photon energy [eV]

wave length [nm]

AM 1.5

black body 5800K

Si

GeGaAs

InPGaP

CdTe

CIS CGS

Different semiconductors have different bandgaps.• Silicon is the most common semiconductor today.• Germanium, GaAs, InP och GaP are used in multijunction

solar cells.• CdTe, CuInSe2, CuGaSe2 and the alloy Cu(In,Ga)Se2 are

used in thin-film solar cells.


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Available current.

Green, M. A.: Solar Cells (1998)

Si

Ge

GaAs

InP

GaP

CdTe

CIS

CGS

• The maximum current from a solar cell depends on the numberof available photons with E ≥ Eg .


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Making silicon wafer solar cells.


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Silicon solar cells.

image: US DoE

Archer; Hill: Clean Electricity from Photovoltaics (2001)

per m3


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Energy bands – two examples.

Cohen et.al., Phys. Rev.141, pp.789-796 (1966)

100

101

102

103

104

105

1.3 1.4 1.5 1.6 1.7 1.80

1

2

3

abso

rptio

n co

effic

ient

[cm

−1 ]

phot

on fl

ux [1

x1021

s−

1 m−

2 eV

−1 ]

photon energy [eV]

experimental

theoretical

AM1.5 spectrum

Moss et.al., Infrared physics 1, p.111 (1961)

100

101

102

103

104

105

1.1 1.2 1.3 1.4 1.5 1.60

1

2

3

4

abso

rptio

n co

effic

ient

[cm

−1 ]

phot

on fl

ux [1

x1021

s−

1 m−

2 eV

−1 ]

photon energy [eV]

experimental

theoretical

AM1.5 spectrum

Raykanan et.al., Solid state electronics22, p.793 (1979)

Φ(x) = Φ0e−α x


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Making thin-film solar cells.

deposition of the back contact

patterning of the back contact

deposition of the absorber layer

patterning of the absorber layer

deposition of the front contact

patterning of the front contact


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Thin-film solar cells.

image: Fuji Advanced Techn.

Archer; Hill: Clean Electricity from Photovoltaics (2001)

image: Pacific Solar

image: Uppsala university

per m3


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Quantum efficiency.

• The quantum efficiency describes the number ofgenerated electron-hole pairs per incidcent photon.

• The quantum efficiency is wavelength (or photon energy)dependent.

• The internal quantum efficiency describes the number ofgenerated charge carriers.

• The external quantum efficiency describes the number ofgenerated and collected charge carriers.


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


The pn-junction – current transport.

EF

EFEc

Ec

Ev

Ev

qVbi

• Electron-hole pairs are generated.• Charge carriers diffuse within the neutral regions.• Electrons drift towards lower energies.• Holes drift towards higher energies.• Electron-hole pairs can recombine.


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Current-voltage characteristics.

voltage

V

currentI

inda

rkne

ss

with

light

Iscshort circuit

Vocopen circuit

power

P

P =V ·

I

maximumpower point

Pmax eller Pmp

η =Pmax

Pin

efficiency η:

Vmp

Imp

area = Vmp · Imp = Pmp

area = Voc · Isc FF ≡Pmp

Voc · Isc

fill factor FF :


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


IV-curve – The one-diode model.

Rseries

RshuntDIlight

+

-

• A good solar cell is described by the one-diode model.

• This model consists of

• the pn-junction diode D• a current source with the light-generated current Ilight• a series resistance Rseries• a shunt resistance Rshunt or shunt conductance Gshunt

• The current-voltage characterstics of this circuit is given by the implicitequation

I(V ) = Idiode(V ) − Ilight + Gshunt[V − RseriesI(V )

]• Often the current density J = I/area, [J] = A cm−2 is used.


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


IV-curve – Assumptions.

• The simulated IV-curves on the following slides arecalculated for a 100 cm2 silicon solar cell with the followingassumptions:

• ideality factor A = 1.0• saturation current density J0 = 4 × 10−13 A cm−2

• light-generated current density Jlight = 30 mA cm−2


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


IV-curve – Influence of the series resistance.

voltage

V

currentI

power

P

Rshunt Rseries Voc Isc Vmp Imp Pmp FF ηΩ mΩ V A V A W % %

1 000 000 1 0.650 3.000 0.565 2.864 1.618 83 16.22 0.561 . . . 1.608 82 16.15 0.555 . . . 1.588 81 15.9

10 0.541 . . . 1.544 79 15.420 0.512 . . . 1.450 74 14.550 0.451 . . . 1.254 64 12.5

100 0.359 . . . 0.879 45 8.8


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


IV-curve – Influence of the shunt conductance.

voltage

V

currentI

power

P

Rshunt Rseries Voc Isc Vmp Imp Pmp FF ηmΩ mΩ V A V A W % %10 000 1 0.647 3.000 0.563 . . . 1.586 82 15.9

5000 0.646 0.562 . . . 1.549 80 15.52000 0.645 0.560 . . . 1.471 76 14.71000 0.641 0.553 . . . 1.305 68 13.1500 0.632 0.530 . . . 0.965 51 9.7200 0.586 0.324 . . . 0.483 28 4.8100 0.300 0.150 . . . 0.223 25 2.2


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Cu(In,Ga)Se2 solar cells.


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Parasitic light absorption.


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Parasitic light absorption.

0

20

40

60

80

100

120

140

160

0 2 4 6 8 10 12

curr

ent [

mA

]

voltage [V]

3102 Zn(O,S)3126 CdS


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Upper limit for efficiencies.

Green, M. A.: Solar Cells (1998)

Ge

CIS

Si InP

GaAs CdTe

CGS

GaP

• The Shockley-Queiser limit is based on thermodynamicprinciples.


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Ever increasing efficiencies?

http://www.nrel.gov/

• The efficiency is generally limited by• basic semiconductor physics• technological processes• electrical losses

http://www.nrel.gov/


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Multijunction solar cells.

Eg1 Eg2

E2

Eg3

E3

E1

E2

E3

• a conventional solar cell has one absorber witha single bandgap Eg1

• photons with energies E ≥ Eg1 are absorbed• photons with energies E < Eg1 are transmitted⇒ in a multijunction solar cell several absorbers

are stacked on top of each other


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future



http://sunlab.site.uottawa.ca

http://sunlab.site.uottawa.ca


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future



+

+

+

I1V1

I2V2

I3V3

I

V

I

V

I

V


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future



+

+

+

I

V1

V2

V3

I

V


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Triple junction solar cells.

http://www.ise.fraunhofer.de

http://pvlab.ioffe.ru

http://www.ise.fraunhofer.de

http://pvlab.ioffe.ru


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future



http://www.concentrix-solar.de/

http://psilab.ucsd.edu/

http://www.concentrix-solar.de/

http://psilab.ucsd.edu/


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Active optics.

images: Prism Solar


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Monograin solar cells.

Meissner, D.: Monograin Solar Cells – Time to Market


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


A growing industry.

http://www.iea-pvps.org

The cumulative installed solar cell power in IEA-reporting countries.

• Since the year 2000 the installed capacity has doubledevery second year.

• Today the majority lies within grid-connected systems.



Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Payback.


• On a system level solar cell installations take less than2 years to break even (energy payback time).

• The expected lifetime for a solar cell installation is morethan 20 years.



Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Cost development for solar cell systems.


Cost development for solar cell systems since 1997.

• The price for solar cells has declined from 60 USD/watt (1976) toless than 4 USD/watt (2008).

• However, since 2000 the decline has slowed down.



Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Brandis/Waldpolenz.

http://www.solarserver.de

UZ 2008

• Installed on a discontinued military air field in eastern Germany.

• Planned to become the world’s largest PV power plant in 2008with 40 MW.

• About 500 000 cadmium-telluride thin-film modules fromFirstSolar.

http://www.solarserver.de


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


Size does matter.


Uwe Zimmermann

Introduction

Solar radiation

Photovoltaics

History


Solar cells


CIGS solar cells


Other solar cells


The future


The Future?

Conclusions

• In order to make an impact, we need to generate some TW ofelectricity by means of solar power.

• A solar cell needs to• capture light• separate charge carriers• extract charge carriers

introduction photonics for energy · semiconductor physics solar cells electrical parameters cigs...

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