Silicon oxynitride thin film barriers for PV packaging

J. A. del Cueto, S. H. Glick, K. M. Terwilliger, G. J. Jorgensen, 

J. W. Pankow, B. M. Keyes, L. M. Gedvilas, and F. J. Pern

N ti l R bl E L b t G ld CO 80401

Silicon oxynitride thin film barriers for PV packaging

J. A. del Cueto, S. H. Glick, K. M. Terwilliger, G. J. Jorgensen, 

J. W. Pankow, B. M. Keyes, L. M. Gedvilas, and F. J. Pern

N ti l R bl E L b t G ld CO 80401 N

ational Renewabl

e Energy L

a

boratory, G

olden, CO 80401 CO 80401

Dielectric, adhesion-promoting, moisture barriers comprised of

silicon oxynitride thin film materials (SiOxNy with various material

stoichiometric compositions x,y) were applied to: 1) bare and precoated soda-lime silicate glass (coated with transparent conductive

Safety & economic considerations motivate a process choice that 

reduces implementation costs and eases industrial adoption of 

fabricated coatings. Plasma-enhanced chemical vapor deposition 

(PECVD) process was chosen whose features and precautionary 

Five chamber in-line system featuring:

 Load lock + 4 deposition chambers,

 2 PECVD chambers,

 Thermal evaporation

1. Abstract1. Abstract 2. Design Strategy 3. Deposition System 

g ( p

oxide SnO2:F and/or aluminum), and polymer substrates (polyethyleneterephthalate, PET, or polyethylene napthalate, PEN); plus 2) predeposited photovoltaic (PV) cells and mini-modules consisting ofamorphous silicon (a-Si) and copper indium gallium diselenide (CIGS)thin-film PV technologies. We used plasma enhanced chemical vapordeposition (PECVD) process with dilute silane, nitrogen, and nitrousoxide/oxygen gas mixtures in a low-power (≤ 10 milliW per cm2) RF

discharge at ~ 0.2 Torr pressure, and low substrate temperatures ≤100°C, over deposition areas ~1000 cm2. Barrier properties of the

(PECVD) process was chosen, whose features and precautionary issues are noted :

 High deposition rate

 Low process temperaturesCommercially feasible to scale to very areas (~ 1m2 or more)

 Employ de-minimus hazard criteria for process gases:

worst-case flammable and non- corrosive hazard classification

 restricted process window explored using only dilute 

compressed gases:

 Thermal evaporation,

 Sputtering.

 1000 cm2 deposition area

 Turbo-pumped vacuum process; Isolated chambers & interconnction via pneumatic slit valves; Process gases distributed via mass flow controllers; Process pressures in the 0.1-1.0 Torr range monitored with 

capacitance manometers;

 Base vacuum and foreline pressures sensed with pirani gauges resulting PV cells and coated-glass packaging structures were studied

with subsequent stressing in damp-heat exposure at 85°C/85% RH.Preliminary results on PV cells and coated glass indicate the palpablebenefits of the barriers in mitigating moisture intrusion anddegradation of the underlying structures using SiOxNy coatings with

thicknesses in the range of 100–200 nm.

p g

 14% nitrous oxide in N2, 

 23% oxygen in N2, 

 3% silane in N2, 

 11.45% oxygen in helium and/or 99.999% helium dilution. h

i

 Base vacuum and foreline pressures sensed with pirani gauges 

and/or ion gauges;

 Temperatures controlled with resistive heaters in feedback 

loops with PID controllers

 Motorized transport of substrate.

6. Conventional -vs.- Modified Packaging 

Pl B i

5. Processing 7. Moisture Transport/Activation Energy 

Water Vapor Transmission Rates* (WVTRs) (g/m2/d) for some

conventional packaging materials and resulting PECVD coatedSiOxNy modified polymer backsheets. :

- - - - - WVTRs (g/m2/d) - - - - -

Sample ID 40°C 60°C 85°C

---------------------------------------------------------------------

PET (neat) 3.98 13.80 69.50

Typical background pressures were on the order of 10-7 Torr.

Process pressures ranged from 40 to 800 mTorr, duringdepositions, (with turbo throttled at ~ 250 to 400 Hz). Plasmasgenerated via 600-W, 13.56 MHz RF (Advanced Energy RFX600) generator and matching network (AE ATX 600). Thin filmdepositions performed at relatively low power (often 8 - 16 W,with some runs up to 200 W) and low temperatures, (ambient

C) CO (S O )

WVTRs allow diffusivity (D) and solubility (S) to be obtained.†

From permeability (P = D · S), and Arrhenius relationP=Poexp(-Ea/kBT), measurements for WVTRs (as function of

temperature) yield estimates for activation energy of moisturetransport by barrier/substrate.Sample ID Ea Activation Energy (eV)

----------------------------------------------------------

PET (neat) 0 55

Exp

(~19inter

madlami

initia

P

olymer Barriers 

073004-1 0.20 0.50 13.45040105-2A 1.17 4.01 21.95052605-2A 0.37 2.23 16.02PEN (neat) 1.74 7.40 31.60050505-1B 0.41 1.61 6.19

*(measured on Mocon Permatran-W 3/31 MG) 1

to ≤ 97 °C) using either soda-lime, TCO (SnO2:F) coated sodalime glass, or Melinex® ST504 (Dupont-Teijin) PET, or Kaladex®1000 PEN (polyethylene naphthalate), and the PV cells (a-Si,CIGS) substrate materials.

PET (neat) 0.55073104-1 0.84040105-2A 0.63052605-2A 0.81PEN (neat) 0.59050505-1B 0.58 † (per ASTM F1770-97e1).

initiahalte

85% on Eperfo

A h ili ( Si) d i di di l id (CIS) ll 

9. Barrier Film Stoichiometry 10. Coated Mirrors: results 10. Coated Mirrors: results 

11. Coated Cells: I-V results 

Under SDCs at 85°C, a second film (on TCO) had

composition evaluated (by XPS) at Si1.0O0.25N0.34C0.04Ar0.04;

following a 4 min Argon sputter, (where carbon isadventitious, and trace Ar is likely an artifact fromsputtering). To investigate both SiOxNy and SiOx barriers,

nitrogen based plasma deposition gases were altered (Heand O2/He); associated WVTR measurements suggest only

Amorphous silicon (a-Si) and copper indium diselenide (CIS) cells werecoated with SiOxNy and then exposed to the 85°C/85% RH damp-heat stress. 

I-V power parameter results for select cells are shown below, for a-Si at top and CIS at bottom, plotted vs. hours in damp-heat:

Pre-sputtered Al metal coatings on soda-lime glass substrates

were over-coated with SiOxNy barrier films. Where defects allow

penetration, moisture will rapidly corrode the Al metal. Notehowever, the coated scribe line at far right side, has survived~940 hours exposure to damp heat (85°C:85% RH). (More easilyseen in right image, with substrate on light box).

Curr

protealbeicoatistresin pmodi

ingre

y

Uncoated controls degrade in a few hours.

-25%-20%-15%-10%

-5%

0%5%

-2%

0%2%4%6%8%

10%

2%

0%

-25%-20%-15%-10%

-5%

0%5%

10%

S1-071505-1 S2-081605-2S3-Control S4-081905-1

oc  Isc  FF  Eff S1-071505-1 S2-081605-2 S3-Control S4-081905-1 a-Si Cells:

 best resistance to 

moisture-induced degradation is shown by coated coupon S1

 control S3 next best small differences in barrier performance result from the

related variations in plasma chemistry and film

stoichiometry. Barrier performance increased inversely withetch dose. Inverse relation and interface adhesion/waterdetails were addressed in more detail by XPS study. 2 __________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ The information contained in this poster is subject to a government license.

Conference Title: CU Energy Initiative/NREL SymposiumConference Location: Boulder, ColoradoConference Dates: October 3, 2006NREL report number - NREL/PO-5200-40682

ingrethrouAcknow

Wo

Referen

1 G. J. J

Module 

2 J. W. 

future i

~940 hours damp heat (85°C:85%RH)

g

Damp Heat Exposure Time (h)

-8%-6%-4%-2%

0%

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700

 Vo

Damp Heat Time (h)

0 50 100 150 200 250 300 350 400

-50%-40%-30%-20%-10%

0%

10%

-40%-30%-20%-10%

0%

10%

-20%-15%-10%

-5%

0%5%

-6%-4%-2%

0%2%4%6%

 Voc  Isc  FF  Eff 551-04-B 552-05-B 552-08-A 556-03-A 556-03-C 556-05-A 556-05-C 551-10-A 551-01-B 551-04-B 552-05-B 552-08-A 556-03-A 556-03-C 556-05-A 556-05-C 551-10-A 551-01-B

 control S3, next best

CIS Cells:

Most of SiOxNy coated 

coupons (colored symbols & lines) exhibit enhanced moisturedurability over the uncoated ones (black lines & symbols)