Silicon heterojunction solar cell cha

Silicon heterojunction solar cell ch

and optimization using and optimization using in situ in situ a

spectroscopic ellipsomet

spectroscopic ellipsomet

Dean Levi Dean Levi, Eugene Iwanicz

, Eugene Iwanicz

Matthew Page, Howard Branz, and 

Matthew Page, Howard Branz, and 

NREL, Golden CO USA NREL, Golden CO USA

2006 IEEE 4th World Conference on Photovoltaic En

2006 IEEE 4th World Conference on Photovoltaic En

May 7

-12, 2006 12, 2006

Hilton Waikoloa Village, Waikoloa, Haw

Hilton Waikoloa Village, Waikoloa, Haw
Disclaimer and Government License

This work has been authored by Midwest Research Institute (MRI) under Contract No. DE-AC36Department of Energy (the “DOE”). The United States Government (the “Government”) retains athe work for publication, acknowledges that the Government retains a non-exclusive, paid-up, irrepublish or reproduce the published form of this work, or allow others to do so, for Government puNeither MRI, the DOE, the Government, nor any other agency thereof, nor any of their employeeor implied, or assumes any liability or responsibility for the accuracy, completeness, or usefulnesproduct, or process disclosed, or represents that its use would not infringe any privately owned ri

specific commercial product, process, or service by trade name, trademark, manufacturer, or othimply its endorsement, recommendation, or favoring by the Government or any agency thereof. authors and/or presenters expressed herein do not necessarily state or reflect those of MRI, the agency thereof. 
SHJ Solar Cell Fabrica

SHJ Solar Cell Fabrica

0 

-

n

-type c

-Si

3 

- HWCVD p HWCVD p

-layer 60 layer 60

Å

9 

- Back Contact Back Contact

5 

– HWCVD i HWCVD i-layer 40 layer 40

Å

2 

– HWCVD i HWCVD i-layer 40 layer 40

Å

6 

– HWCVD n HWCVD n

-layer 60 layer 60

Å

8 

- ITO

7 

- ITO

10 

- Front Contact Front Contact

11 

- Photolit

Photolit

Flat waf

Flat waf

Texture

Texture

1 

4 

E

E
HWCVD deposition sys

HWCVD deposition sys

i, n, and p layers are deposited in separa

i, n, and p layers are deposited in separa

n layer n layer

i 

p layer p layer

ellipsometer ellipsometer
Fabrication and characterizati

Fabrication and characterizati

• in situ in situ RTSE - Measures individual layers during deposition

• layer thickness layer thickness• growth rate growth rate• surface roughness surface roughness• optical properties optical properties• crystallinity crystallinity

RTSE

• ex situ ex situ VASE - Measures all layers at once in completed device Measures all layers at once in completed device VASE

On actual devices On actual devices• layer thickness layer thickness• optical properties optical properties• integrated optical integrated optical response response• enables optical enables optical device modeling device modeling
in situ in situ ellipsometry of a ellipsometry of a-Si:H 

Si:H 

► Surface roughness indicates growth 

Surface roughness indicates growth 

► Optical properties reveal structura

Optical properties reveal structura

electronic properties electronic properties
Evolution of surface roughn

Evolution of surface roughn

• The evolution of R The evolution of Rs with bulk film with bulk film 

thickness d thickness db provides insight into the provides insight into the film growth process. film growth process.

•

R

s can be represented as a function of d can be represented as a function of db

G

β = 0.5 random depositionβ = 0.25 RD w/diffusionβ = 0 RD w/relaxation

Universality classes
Growth exponent for i Growth exponent for i-laye

laye

•

β is nearly constant for T is nearly constant for T

s < 14

• Abrupt increase in Abrupt increase in 

β above 145 above 145

o

change in growth mode change in growth mode 

– uc

-Si 

Si 
Optical properties Optical properties vs

T

• i layers i layers are deposited on oxide are deposited on oxide

-free <100> c free <100> c

-S

S

• 73C 

– 126C 

126C 

• 144C layer is 

144C layer is 

• 162C layer is 

162C layer is 
Analysis of i Analysis of i-layer ε2 Ts dep

dep

dε2/dTs = -210 mev/100oC

dEg/dTs = -60 meV/100oC 

Δ(dε2/dTs) = 17 meV / 1 at.% C(H) ) = 17 meV / 1 at.% C(H)*

12% drop in C(H) w/100 12% drop in C(H) w/100oC increase in T C increase in Ts

* G.F. Feng, et a

, et a
ex situ ex situ ellipsometry of finishe

ellipsometry of finishe

► Ellipsometry measurement and ana

Ellipsometry measurement and ana

► optical model to calculate R,T,A for 

optical model to calculate R,T,A for 

► Compare calculations with device p

Compare calculations with device p

► SHJ compared w/diffused juncti

SHJ compared w/diffused junct

► 2 SHJ devices w/different p 2 SHJ devices w/different p-dop
ex situ ex situ SE on finished de

SE on finished de

Example: Example: single-sided n sided n-i-p SHJ 

layer 4 n4, k4, d4layer 3 n3, k3, d3layer 2 n2, k2, d2

layer 1 n1, k1, d1

c-Si (p-type) 200 μm

Ψ(λ), Δ(λ) 

least squares squares

Surface roughness 65 Å

ITO 835 Å

n layer 57 Å

i layer (100oC) 40 Å

c-Si (p-type) 200 μm

SE measures 

SE measures 

ratio Ψ and th

and th

Δ as a functio

as a functio

at multiple an

at multiple an
Comparison of SHJ w/diffused ju

Comparison of SHJ w/diffused j

• Two devices are identical except for front junction (both 

Two devices are identical except for front junction (both 
ex situ ex situ SE: p SE: p-doping com

doping com

• 2 nominally identical devices 2 nominally identical devices 

• 2 sccm vs 18 sccm B 18 sccm B2H6

Surface rough

ITO 

p layer (18 sc

i layer (100oC

c-Si 

Surface rough

ITO 

p layer (2 scc

i layer (100oC

c-Si 
Device optical performance co

Device optical performance co

• Layer thicknesses and optical Layer thicknesses and optical 

constants determined by constants determined by ex situ ex situ SE

compon

compon

p-layer 

layer 

i-layer 

layer 

reflect

ITO a

ITO a

% s

% s

18 sccm vs. 

• Primary difference is p layer doping Primary difference is p layer doping 

– flow rate of B flow rate of B

2

H

6

• Optical model enables calculation of Optical model enables calculation of 

contribution of each layer contribution of each layer
Summary Summary

• The combination of The combination of in situ in situ and ex 

ex 

provides a powerful method for p

provides a powerful method for p

the effects of processing change

the effects of processing change

SHJ devices and guiding optimiz

SHJ devices and guiding optimiz

• in situ in situ SE gives insight into grow

gives insight into grow

mechanisms and accurate layer 

mechanisms and accurate layer 

• ex situ ex situ SE measures completed 

measures completed 

structures to determine integrate

structures to determine integrate

properties properties
Acknowledgements Acknowledgements

• This work is funded under DOE Contract N

This work is funded under DOE Contract N

99GO10337. 99GO10337. 

• Thanks to Thanks to Russel Bauer, Lorenzo Bauer, Lorenzo Roybal, H

Moutinho Moutinho, Bobby To, , Bobby To, Yanfa Yan, and Qi W

W

and to Ajeet Rohatgi Rohatgi and Vijay and Vijay Yelundur Yelundur o

o

Tech.