TFSC_Why measuring Diffusion Length - TFSC

THIN FILM SEMICONDUCTOR INSTRUMENT
Why measuring carrier diffusion length LD?
Materials with Higher LD lead to solar cells with Higher PCE (power
conversion efficiency) by achieving higher Fill Factor (FF)
Case of PIN junction in silicon thin film: a-Si,
µc-Si, …
Case of bulk-hetero-junction
Organic PV: P3HT:PCBM, …
(BHJ)
in
+
+
Mixture of Hole
transporting layer
and electron
transporting layer
Intrinsic layer
(absorber)
-
- Absorption of photon and creation of an electron-Hole
pair
- Transport and extraction of charges through the
intrinsic layer towards the electrodes
- Absorption of photon and creation of exciton
- Dissociation of exciton to an electron-Hole pair
- Transport of charges through electron transport layer
and hole transporting layer respectively
- If the internal electric field is strong enough, the charge transport is field-driven (drift type). In this case there is less charge losses
- this is the case in PIN junction with thin intrinsic layer (< 150 nm) and also in the short circuit regime of PIN
- If the internal electric field is weak, the charge transport is diffusion type and the charge loss depends on the diffusion length
compared to intrinsic layer thickness:
- this is the case in the open-circuit regime and if the diffusion length is smaller than intrinsic layer thickness
- Conclusion:
- if the diffusion length is smaller than the intrinsic layer thickness, the Fill-Factor (FF) of the PIN will be reduced due to carrier
recombination near the open-circuit regime
- Similar behavior between thin film PIN solar cells type and Organic solar cell types
(especially the BHJ types).
àThe FF is highly dependent on carrier diffusion length
à NEW: TFSC-Instrument has proved for the first time that SSPG is
suitable for Organic BHJ to extract LD : data publication ongoing
TFSC-Instrument SAS
3 Rue Léon Blum, 91120 Palaiseau France,
Tel : 33 (0) 1 69 19 43 48,
www.tfscinstrument.com
Société au capital de 30 000 €- R.C.S. Evry-Siret 794 759 795 00014- code APE 2651B-TVA N° FR 94 794 759 795
Which materials?
1
0.5
b
- Photoconductive semiconductor layer
- Layer deposited on insulating substrate
- Layer with minority carriers diffusion length between tenths of
nm to few micrometers
- Layer absorbing at the laser wavelength: 633 nm is the
standard value, otherwise a change of laser is needed (option)
0
L = 80 nm
-0.5
(a)
a-Si:H
-1
LD of organic layers (P3HT:PCBM)
0
5
10
15
20
L (mm)
1
1,2
0,8
(d)
1,0
Equation
béta
béta
L
Phi
0,14643
0,66068
Standard Error
0,00332
0,00693
0.6
0,6
0.4
0,4
b
0,4
béta
Balberg Plot
0,99634
Value
0,8
0,6
0.8
y = 1-2*Phi/(1+(6.28*L/x)^2
)^2
Adj. R-Square
0,2
LD=146 nm
0.2
LD=146 nm
0,2
0,0
0
L = 115 nm
-0,2
0,0
-0.2
-0,4
1,2
1,4
1,6
1,8
2,0
0
2,2
5
10
15
20
Sb S
25
2 3
Pas du réseau (µm)
Pas du réseau (µm)
-0.4
0
5
10
15
20
L (mm)
Examples of materials
1
(c)
-Organic layers: Bulk-Hetero-junctions, polymers and others
0.6
b
- Silicon thin film and its alloy: a-Si, a-SiGe, µc-Si, …
0.8
- Perovskite layers: Hybrid perovskite layers used for PV
0.4
- Other
0.2
layers:
according
to
transport
and
absorption
properties
L = 995 nm
Poly-Crystalline Si
0
0
5
10
15
20
L (mm)
Which parameters can be extracted?
- Mobilityxlifetime product <µt> for minority and majority carriers
- LD of minority carriers
- lifetime of majority and minority carriers if the mobility is known
Other products and services
- Quantum Efficiency and Solar cell simulator
- Applied for small area PV cells
- Fast and reliable system
To contact us
- www.tfscinstrument.com
- Services:
- [email protected]
- Sampling
- Tel: +33(0) 6 59 26 06 02
- LD measurements on customer samples
- Free tests on customer samples
- Please contact us for more details
TFSC-Instrument SAS
3 Rue Léon Blum, 91120 Palaiseau France,
Tel : 33 (0) 1 69 19 43 48,
www.tfscinstrument.com
Société au capital de 30 000 €- R.C.S. Evry-Siret 794 759 795 00014- code APE 2651B-TVA N° FR 94 794 759 795

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