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Silicon Thin Film Solar Silicon Thin Film Solar Cells: Potential & Cells: Potential &
Challenges"Challenges"
Abdelilah SLAOUIAbdelilah SLAOUIInstitut d’Electronique du Solide et des Systèmes InESS
CNRS – Univ. StrasbourgStrasbourg, France
ECOLEPOLYTECHNIQUE
LPICMUMR 7647Pere Roca i Caboroccas
… more than 300 publications
Since 1975 …
InESS (PHASE) active in PVInESS (PHASE) active in PV
PVInESS
1) High efficiency cells on mc-Si & ribbons (< 100µm)
2) TF-Si cells on foreign substrates
4) Polymer based organic cells (+LIPHT)
3) Advanced concepts(QDs,
plasmonics, RE-TCOs)
contactemetteur
basecontact
substrat
Bulk Si : Eg=1.1 eV
QD cell 1 : Eg=1.5 eV
QD cell 2 : Eg=2 eV
Photovoltaic research at Photovoltaic research at InESSInESS
OutlineOutline
Thin Film Solar Cells Market
Silicon thin film technologies: Polymorphous Si/µc-Si
Polycrystalline Si * Direct deposition approach* Seed layer approach
Si nanostructures (Si-NWs, Si-nps)
Future of TF-Si based technologies
Photovoltaic Techn.in 2009: Market sharesPhotovoltaic Techn.in 2009: Market shares
Source: Paula Mints, Navigant Consulting
• Progress in PV modules production• Si wafer based PV modules still dominant: 84% in 2009• Schipments of TFs ~14% in 2008 & 16% in 2009
Learning Curve for PV modulesLearning Curve for PV modulesHistorical and Projected Experience Curve for PV Modules
Source: GreenTech/Prometheus
a-Si, a-Si, µc-Si, µc-Si, TF c-Si TF c-Siamorphous, microcrystalline, amorphous, microcrystalline, CrystallineCrystalline
TF Silicon basedTF Silicon based ModulesModules
polymorphous polycrystalline
e-
4
Pumping
RF electrode
Plasma
Substrate
SiH4
PH3
GeH4
H2
TMB
Hydrogenated amorphous Silicon (a-Si:H) at Ts < 250°C
Layers deposited from SiHx radicals
- Most widely-used deposition method – PECVD- Strong degradation of efficiency unstable Si-H bonding
Low Ts ~ 200 °CScale up demonstrated
From Amorphous to Polymorphous SiFrom Amorphous to Polymorphous Si
ECOLEPOLYTECHNIQUE
LPICMUMR 7647
Plasma-formed nanocrystals/clusters contribute to deposition polymorphous silicon(pm-Si:H)
4 nm
Nanostructured material Silicon nanocrystals
in an amorphous matrix
Medium Range OrderImproved transport properties
and stability
From Amorphous to Polymorphous SiFrom Amorphous to Polymorphous Si
100 cm2
mini-module
ECOLEPOLYTECHNIQUE
LPICMUMR 7647
400 500 600 700 800 900 10000,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
Rép
onse
Spe
ctra
le
Longueur d'onde (nm)
LitD4_C
µc-Si:H PIN solar cells
Jsc = 24.5 mA/cm2
FF Voc Jsc (%)67.3 0.520 V 24.5 mA/cm2 8.6%
Towards Micromorph Si solar cellsTowards Micromorph Si solar cells
ECOLEPOLYTECHNIQUE
LPICMUMR 7647
pm-Si:H
Potential micromorph =15%
µc-Si
-Growth from nanocrystals leading to unusually large crystalline domains- Manifests as epitaxy or very-large grain fraction
Si
Si
Towards high efficiency solar cells through Low Pressure Plasma Processes
E.V. Johnson et.al. Appl. Phys. Lett. 92 (2008) 103108
From polymorphous to Crystalline-SiFrom polymorphous to Crystalline-Si
ECOLEPOLYTECHNIQUE
LPICMUMR 7647
~1 µm thick c-Si film at
LT
c-Si transferred onto a PI film (or on a metal foil)
ECOLEPOLYTECHNIQUE
LPICMUMR 7647
OutlineOutline
Thin Film Solar Cells Market
Silicon thin film technologies: Polymorphous Si
Polycrystalline Si * Direct deposition approach* Seed layer approach
Si nanostructures (Si-NWs, Si-QDs)
Future of TF-Si based technologies
TF-TF- Crystalline Crystalline SSii solar cells solar cells ??Potential: 2-3 µm Si to reach reasonable efficiency Similar technology than bulk Si No hazardous nor rare elements
ChallengesFast deposition/formation High quality material (Leff >> W)
Good surface passivationEfficient light confinment
F. Llopis, I. Tobıas, SOLMAT 87, (2005), pp.481-492.
• HT-CVD at T>900°C• HT substrates : Alumina, SiSiC, SiN, mullite• High Dep. Rate ~1-5µm/min
5s 120s
10µm
15s
30 sec 60 sec 180 sec
Polycrystalline Si by Direct CVDPolycrystalline Si by Direct CVD
1
3
2
4
pppp++-Si//-Si//FoxFox/ADS09/ADS09
A. Slaoui, et al., SOLMAT, 71/2, 245 (2001)
• small grains large density of GBs many defects• large distribution depletion of grains• Preferentiel grains orientation (110)
Enlarging grains CVD-OVL, seed layer approachNeutralizing defects TREBLE, hydrogenation
CVD @1200°C
Polycrystalline Si by Diect CVD Polycrystalline Si by Diect CVD
A.Focsa, A. Slaoui et al., Renewable Energy 33 (2008) 267–272
Bare mullite
Mullite + PSG
Mullite + BSG
CVD-OLL CVD-OLL Si deposition on Si deposition on Flowable oxidesFlowable oxides (DC) (DC) increased adatom mobility reduce nucleation density
EU-LATECS project: IMEC, Dow-Corning, FhgISE, InESS
Polycrystalline Si by CVD-OLLPolycrystalline Si by CVD-OLL
substrate
Si Seed layer
Si Absorbing layerAluminium induced Crys. Zone (lamps) melting induced RxLaser induced Crys.
VPE / SPE
contact
emetteur
basecontact
substrat
Si < 2µm
BS Glass, Ceramics Glass, HT GlassAlumina, Mullite, SiSiC, Metal foils
Polycrystalline Si: Seed Layer ApproachPolycrystalline Si: Seed Layer Approach
before anneal anneal 5min / 500°C
anneal 10min / 500°C anneal 60min / 500°C
Source: Nast et al.
Polycrystalline Si by AICPolycrystalline Si by AIC
E. Pihan , A. Slaoui, Thin Solid Films 511 – 512 (2006) 15 – 20
Aluminum Induced Crystalization of a-SiAluminum Induced Crystalization of a-Si
Glass
50 µm
Fox/Silicon
Fox/Mullite
Fox/Alumina
th-SiO2
Poly-Si by AIC vs substrate
E. Pihan et A. Slaoui., J. Crystal Growth 305, 2007, pp. 88-98
0
20
40
60
80
100
0 50 100 150 200 250 300 350cr
ysta
llize
d fr
actio
n (%
)
annealing time (min)
500°C 475°C
450°C
AIC poly-Si layer on glass-ceramic substrate
Growth Kinetics
EBSD analysis: grains size &
grains orientation
Defect analysis using EBSD Technique
475°C/3h
black lines→high anglered lines → Σ3 twingreen lines → Σ9 twin
Polycrystalline Si by AIC on Glass CeramicsPolycrystalline Si by AIC on Glass Ceramics
ANR project - Polysiverre: InESS, Corning, TOTAL, AET, LPICM, INL, EMSE
P. Pathi/A. Slaoui., Applied Physics A, 97 (2009) 45.A. Pathi/A. Slaoui, 24th European PVSEC 2009, 2533.
• Metal (FeNi) as a back contact• development of a conducting barrier layer against metallic imp.
ANR project - CRISILAL: CEA, InESS, ArcelorMital, AnealSys
CSL boundaries
Polycrystalline Si by AIC on Metal FoilsPolycrystalline Si by AIC on Metal Foils
Homojunction - Mesa
Emitter n+
Lcol
Ln
• large charge collection high Isc• large SCR low Voc
ITO
substrate AIC layer (p+ / n+)
Absorber layer (p / n)
Base contactsEmitter contacts
a-Si
Heterojunction - IDC
• Higher Voc• Lower series resistance
AIC + epi-CVD (2.1µm)Voc ~ 450-530 mV
Efficiency ~ 8 – 10%Limited by intragrains defects
O. Tuzun , A. Slaoui et al. , 23 EUPVSECSOLMAT 2010, in press
substrate
AIC layer (p+)
BSF layer (p+)
Absorber layer (p)
Base contactEmitter contacts
Emitter (n+)SiNx
Polycrystalline Si solar cells by AICPolycrystalline Si solar cells by AIC
110nm Si layer experiments
Seed layer by LICEpi-layer
Glass substrate
EU project -HIGH-Ef: IPJ, Horiba, CSG, Bookam, EMPA, InESSANR project -SiLaSol: InESS, ArcelorMital, CEA, Excico, IREPA-laser
anneal
Polycrystalline Si by LICPolycrystalline Si by LICLaser Induced Crystalization of a-SiLaser Induced Crystalization of a-Si
445nm Si layer
Sample
Ar, O2
Ellipsoidal reflector
Linear halogen lamp
CCD-camera
Array of halogen lamps
Si by CVD + Zone Melting recrystallization
Elongated grainsSize: 1-20 mm 11,5% with 10 µm
Si 15,4% with 20 µm Si
0,0 0,1 0,2 0,3 0,4 0,5 0,60
10
20
30pc-Si on mullite substrate
after ZMR
Curre
nt d
ensit
y [m
A/cm
²]
Voltage (V)
S. Bourdais, S. Reber, A. Slaoui, 16th EU-PVSEC, (Glasgow, Ecosse, 2000) p. 1492
no ZMR
Polycrystalline Si by ZMRPolycrystalline Si by ZMR
EU project -COMPOSIT: ISE, IMEC, InESS, RWEEU project-POLYSIMODE: IMEC, InESS, CSG, Helmoltz, ISE
SnO2Glass or flexible sub
Step 4: complete i-n layers on topp-type SiNW
p-t
ype
i-layer n-layer
Strong light trappingRadial junction
Silicon based nanostructures solar cells Silicon based nanostructures solar cells
Vertical SiNWs Si nanostructure tandem cell
Eg=1,5eV
Eg=1,1eVEg3
Eg2
Eg1
Eg1> Eg2> Eg3
Si-nps
Si-nps
c-Si
Eg=2eV
A. Slaoui, R.T. Collins, MRS Bulletin V32 (2007) N°3
Nanostructured Silicon:* SiNWs: light trapping
* Si-nps: photon energy shifter (DC ?)
* Si-nps: New wide BG absorbing Si (tandem)
One pump down “all-in-situ” fabrication of SiNWs on TCO substratesNano-scaled In or Sn drops produced on ITO or SnO2 by H2 plasma superficial reduction at 200oC~350oC.
SnO2 or ITO
H+ H+
Cg
Cg
SiHx (or SiHx +H+)
Cg
SiHx (or SiHx +H+)SiHx
Deposition interface
Diffusion of Si in catalyst drops
Dissolve & absorption
(a)
Sn or In drops
Cg (b)
(c)
(a) (c)
(b)
<110
> (d)
a-Si
2~2.5nm sheathof a-Si
2~2.5nm amorphous layer
(d)
(a) (c)
(b)
<110
> (d)
a-Si
2~2.5nm sheathof a-Si
2~2.5nm amorphous layer
(d)
P.-J. Alet, P. Roca i- Cabaroccas et. al. Journal of Materials Chemistry 18 (2008) 5187
Vertical Si–NWs based solar cells Vertical Si–NWs based solar cells
ECOLEPOLYTECHNIQUE
LPICMUMR 7647
Challenges- Control catalyst size- Density, position- Transport, doping,…
World record efficiency for a bottom up Silicon Wire Radial Junction Solar cell
Vertical Si–NWs based solar cells Vertical Si–NWs based solar cells
ECOLEPOLYTECHNIQUE
LPICMUMR 7647
Silicon nanostructure wide Eg material Silicon nanostructure wide Eg material • Engineer a wider band gap material using Si nanostructures• Si QDs-relaxed size constraint cf QW, for given a quantum confinement
Ener
gy P
L (
eV)
Si Nanoparticules size (nm)
MW-PECVD : NH3 + SiH4 Si rich SiNx:H (Si-RSN)
* Single layer
* Multilayers
Si nanostructure tandem cells Si nanostructure tandem cells
anneal
anneal
20 nm20 nm
Delachat, Carrada, Slaoui; Nanotechnology 20 (2009) 415608_1-5Keita, Delachat, Slaoui, J. Appl. Phys. 107 (2010) 093516
BG 29% 33% 37% 44% 50%1 nm - - - ? ?3 nm - - - 1,85 2,05
4 nm - 2,05 x x x5 nm ? x x x 1,37
Si-nps
Si-nps
c-Si
Si nanostructure tandem cells Si nanostructure tandem cells Bandgap value depends on SiNx thickness and on Si excess in SiNx
• Potential : Efficiency ~35%• Chalenges: * Tunneling distance between layers & QDs * Doping * Extraction of carriers
* Cost
The Future of TF-Si based PV Technologies The Future of TF-Si based PV Technologies • Better Control and rational use of materials - Better plasma control - Gas recycling - Faster high-quality TCO’s - Higher deposition/crystallization rates
• New materials - Si-nanowires / Si-nanops - p-type TCO’s - Printable TCO’s - Nanocrystalline diamond, SiC
• Better light management - Improved TCO’s ( Lower IR absorption = lower N; Textured) - Random texture (texture glass; back reflector) - Periodic Structures (Grating, photonic crystals, plasmonics) - Conversion spectrum
Long Term Objectives:-Concepts for stable cells with >17%
Costs<0.4 Euros/Wp at 500 MW, = 15% (rigid)< 0.3 Euros/Wp at 500MW, = 13% (flexible)
Acknowledgements
From InESS/Strasbourg: C. Chatterjee; A. Chowdhury; F. Delachat; A. Focsa; P. Prathap; S. Roques, O. Tuzun; …
ANR–HABISOL projects: CRISILAL, POLYSIVERRE, SILASOLEU Projects: LATECS, CRYSTALCLEAR; HIGH EF, POLYSIMODE
From LPICM/Ecole Polytechnique/Palaiseau:P. Roca i-Cabarocas
Bilateral Conference on Energy
9 – 13 May 2011; Nice / France
http://www.emrs-strasbourg.com/
Bilateral Conference on EnergySymposia:
