Zoomerang | OPV International Lifetime Summit Results Overview

Zoomerang | OPV International Lifetime Summit: Results Overview
OPV International Lifetime Summit
Results Overview
Date: 7/9/2008 6:31 AM PST
Responses: Completes
Filter: No filter applied
2.
Do you believe that OPV devices are inherently unstable?
Stable 1 4%
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7 29%
10 42%
5 21%
Unstable 1 4%
3.
Rank the following concerns for OPV stability with 1 being the most important
Top number is the count
of respondents selecting
the option.
Bottom % is percent of
the total respondents
selecting the option.
Active Layer:
stability of the
acceptor
Active Layer:
stability of donor
Active Layer:
stability
donor/acceptor
blend
Interfaces:
TCO/HTL,
HTL/active layer,
Donor/Acceptor,
Active Layer/Back
Contact
Electrode Contacts:
TCO, Metal
Hole Transport
Layer (HTL)
Electron Transport
Layer (ETL)
Packaging; Oxygen,
water,
photo/thermostability
of contact
Not at all important Not very important
0
0%
0
0%
1
4%
1
4%
1
4%
1
4%
3
12%
1
4%
2
8%
2
8%
2
8%
0
0%
1
4%
2
8%
2
8%
0
0%
Somewhat important
should be done
10
42%
7
29%
3
12%
2
8%
6
24%
8
33%
Total 24 100%
Significantly Important
8
33%
12
50%
10
42%
5
20%
8
32%
8
33%
7/9/08 7:31 AM
Highest Importance must
be done
Photostability of 1 0 7 4 12
9
38%
1
4%
9
38%
5
20%
4
17%
3
12%
8
33%
17
68%
9
36%
5
21%
1
4%
18
72%
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Zoomerang | OPV International Lifetime Summit: Results Overview
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7/9/08 7:31 AM
OPV active layers 4% 0% 29% 17% 50%
Temperature
Illumination source
type/spectrum
Pattern of
Illumination,
cycling/intermittency
Applied Load
5.
0
0%
0
0%
0
0%
0
0%
3
12%
5
22%
8
35%
5
21%
How stable do you believe current encapsulated OPV devices are?
100 hours 2 9%
500 hours 1 4%
1000 hours 9 39%
5000 hours 7 30%
10,000 hours 4 17%
7
29%
11
48%
9
39%
15
62%
9
38%
6
26%
6
26%
2
8%
Total 23 100%
6. To your knowledge do any meaningful and appropriate standards currently exist for OPV stability/lifetime?
none 6 25%
initial stages 13 54%
developed 1 4%
adequate 2 8%
well developed 2 8%
8.
What metrics do you believe should be incorporated into the standards for OPV stability?
Top number is the count
of respondents selecting
the option.
Bottom % is percent of
the total respondents
selecting the option.
Degree of lost
efficiency (where
should the start
point in efficiency
be?)
Time over which a
device is measured
(is there a
Total 24 100%
least important 2 3 4 most important
1
4%
0
0%
0
0%
0
0%
4
17%
5
22%
5
21%
10
43%
5
21%
1
4%
0
0%
2
8%
14
58%
8
35%
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Zoomerang | OPV International Lifetime Summit: Results Overview
minimum?)
Temperature
Relative Humidity
Light Intensity
Spectrum
Constant
Illumination
Devices kept under
a specific load
Outdoor
Measurement
0
0%
1
4%
0
0%
0
0%
1
4%
0
0%
0
0%
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0
0%
0
0%
0
0%
3
14%
2
9%
2
9%
2
9%
13 Responses
6
25%
3
12%
5
21%
3
14%
6
26%
8
36%
5
23%
9. Should a round robin validation using stabilized and identical devices be done?
Not Necessary 2 8%
8
33%
7
29%
10
42%
11
50%
12
52%
10
45%
7
32%
2 8%
3 12%
10 40%
Mandatory 8 32%
10.
Which techniques are the most important for determining diffusion rates for encapsulation?
Top number is the count
of respondents selecting
the option.
Bottom % is percent of
the total respondents
selecting the option.
Mocon
Ca diffusion
Inference from
encapsulated device
stability vs 'glove
box' devices
Mass-spectrometry
Radioactive method
Total 25 100%
Not very useful 2 3 4 Very useful
1
6%
0
0%
2
11%
0
0%
0
0%
2
13%
2
11%
3
19%
7
44%
2
13%
1
6%
8
50%
4
25%
7
47%
8
44%
2
12%
7/9/08 7:31 AM
10
42%
13
54%
9
38%
5
23%
2
9%
2
9%
8
36%
4
25%
4
27%
5
28%
3
19%
1 4 4 2 2
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Zoomerang | OPV International Lifetime Summit: Results Overview
Radioactive method
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7/9/08 7:31 AM
8% 31% 31% 15% 15%
12. Should NREL create a centralized database for sharing stability information?
No 1 4%
1 4%
Maybe 7 28%
6 24%
Yes 10 40%
13.
Would you be willing to contribute to such a database?
Total 25 100%
No 0 0%
1 4%
Depends 11 48%
2 9%
Yes 9 39%
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Total 23 100%
Page 4 of 4

Major Concerns (Raw Data)
encapsulant stability - long term yellowing of flexible packaging
Stability of the morphology; contact issues at electrode due to delamination,
diffusion of ions (from e.g. PEDOT) through the layer
Electron transport is the difficult part in organic photovoltaics
Delamination and dark spot formation are major concerns.
Module specific issues: reverse bias testing due to partially shadowing
I believe that the biggest problem facing OPV reliability is the lack of detailed
mechanisms for each type of failure. It's difficult to fix something you don't
understand.
Moisture & O2 permeation
Differentiate between intrinsic and extrinsic effects. For conventional Si
technology, intrinsic issues do not play an important role over the live of the
solar cell. The Si wafer is stable. For OPV, we need to study both intrinsic
and extrinsic stability
Other issues are: effect of shadowing, reverse bias, wind, hail, salt, sand,
thermal cycles, connection with balance of system.
Perhaps also discuss the application area, since the stability requirements
depend on the application (consumer electronics, telecommunication,
camping equipement, stand alone PV systems, grid connected & building
integrated PV systems, large scale power plants)
UV stability. Reliance on the packaging to solve stability problems when
experience has shown that samples must be moisture insensitive.
film morphology and device architecture, e.g., transparent and tandem OPV
devices
The uniformity of the OPV active layers and how the interaction of the layers
affect each layers stability
Morphology of donor/acceptor blends; integrity of donor and acceptor phase
and interface
What Standards Exist?

As a starting point the standards from silicon and thin film devices are
being applied (85/85). I do not believe they are meaningful as there is no
data to indicate that the acceleration factors from these other technologies
will be at all applicable. Furthermore, it is not clear that these are the
most important root cause of degradation in OPV.
1 sun intensity and 80 degrees. conditions should be either Jcs, Voc, or
maximum power point.
Some measure is desperately needed. perhaps several levels of testing. A
short test that can be useful for screening materials and a longer one that
should be viewed as the real litmus test for stability. The most recent issue
of SOLMAT has some papers detailing stability and methods. Most notably
accelerated testing is not a reliable method
some tests derived from IEC protocols for x-Si are carried out. If these are
adequate depends totally on the foreseen type of applications
Why not use the standards that have been developed for amorphous
silicon?
At the moment people select isolated tests from existing IEC standards to
identify critical stress factors. Some parties are starting to develop prenormative
test protocols which fit better to their product (flexible) and final
application (low-tomedium power applications)
OPV devices should be held to the same standards as those made from
other more traditional PV materials.
Adapt IEC test. The operating conditions of the product should determine
standards, not the shortcomings of the material.
IEC thin-film qualification test. question 3 was answered if subjected to
85C/85% RH how long will last. Not on shelf at room temperature.Question
6 - IEC test a minimum. Need to understand degradation to determine if
it is enough.
there is no standard yet
ASTM E1171-04
ASTM E2236-05a
IEC61215
they include implicit assumptions about starting technology

Initial NREL guidance but not adequate yet
Degree of Lost Efficiency
It might be reasonable to report the start point as either the starting
efficiency (after encapsulated, if there is any encapsulation) or after the
device efficiency has stabilized (but then this might need to be defined). I
would borrow the level to which a Si or thin film cell is allowed to degrade
in their quoted lifetimes.
with at least a 5 percent device
The degree of loss is important. Do not test this for mediocre devices, only
for those that reach a reasonable (e.g 3% or more) efficiency. Otherwise
you will get the answers to quateuons that are not important.
I don't understand this - why talk about "losing efficiency"?
To make things clear, degree of lost effieciency should always be
mentioned. Importance of starting point: dpeends on application
The value of stable efficiency will be important.
set of data required
scientific model/understanding
deduce, understand & confirm acceleration factors
start with outdoor tests already at initial stage of stability studies
To the point like amorphous silicon. The stabilized efficiency is after an
initial transient.
starting point is "as rated" - in aSi they condition cell first or rate low to
compensate.
Output power under load is most relevant parameter
Minimum Time for Device Measurement

minimum of 500 hours
At least 1000 hrs, but some studies should also be done at 5000 hrs.
As above maybe two layers are needed
one for testing materials
one for testing complete modules/devices for applications
If a sample that is measured twice in succession gives two different
values, the measurement reflects the speed with which the measurement
is completed, and, clearly, is not relevant to real use
People use 1000 hours as a minimum since this is mostly used in current
IEC lifetime tests for PV.
As long as it takes to eliminate hysteresis. if you meant exposed
minimum 100 hrs.
may depend on the application
You need to correlate short aggressive environment with longer term
typical environment so that accelerate testing can be done.
5-10 min
Temperature Standard
Are we trying to develop an accelerated degradation standard, "rooftop"
conditions, or something else?
80 degrees. but at least defined
The stability needs to be measured at a temperature that can predict the
stability under real-use conditions.
Various temperatures are important to determine acceleration factors.
Development of standards should also be based on a scientific basis
Same as conventional flat plate.
85C
65

Humidity Standards
Relative humidity is important, but studies should be done both in
presesnce and absecnce of water vapor
The stability needs to be measured at a humidity that can predict the
stability under real-use conditions.
Extremely important to test quality of encapsulants. This is regarded as
one of the most important test in current PV
Seems to be a significant cause of degradation.
standard testing with encapsulated or as-sold product
Light Intensity
There may be intensity dependent degradation. Changing the intensity
may be a way of changing the acceleration factor.
1 sun
1 sun
The stability needs to be measured at an illumination that can predict the
stability under real-use conditions.
In order to accelerate the number of turnovers, it is wise to go for 1 sun
equivalent illumination
1-sun
standard (STC,AM 1.5G)
100 mW/cm2
Spectrum
There needs to be a systematic study of what frequencies adversely
affect OPV devices. This may vary from material to material or even
donor:acceptor system to system. It may be possible that UV
degradation studies can be done independently from a studies with
spectrum that is relatively well matched to the EQE. I would think
continuous lamp spectra would be more meaningful than ones from
lamps with many strong lines.
am1
In my view less important, altough UV may detriorate HTL and oxides
used.

Not particularly important, but the issue is how much, if any, UV should
be filtered by the packaging.
The stability needs to be measured under a spectrum that can predict the
stability under real-use conditions.
Presence of UV in the light source might be important.
UV acceleration minimal. UV light expected to damage polymers.
STC
AM1.5G
Continuous Illumination
There may be some healing effect as observed in a-Si, if the sample is
shuttered periodically.
Yes, to save time.
There are many examples of devices improving with a period in the dark.
It may thus be useful to simulate night/day cycles
The use of constant, instead of intermittent, illumination is likely to be a
matter of convenience.
Yes, to accelerate the number of turnovers
Have to be done for accelerated testing
Loading
Keeping a device under the MPP for most of the time, seems to be the
most reasonable "real-world" condition. It may not matter though.
For sure at maximum power point, but SC and OC conditions are also
intersting as they may help to resolvethe mechanisms
Some devices especially the ZnO devices exhibit a memory effect
whereby the load that the device has experience affects the response.
the load should be stated and is sometimes important in what result that
is obtained
The only operating load of importance is that which gives the maximum
power point in the device.
The bias condition is known to affect degradation rates of many devices;
it is likely that it will be important in at least some OPV designs

Only if demonstrated different failures in the dark at Voc versus the light
at Pmax or dark biased to Pmax. Secondary problem as long as so
sensitive to air.
Outdoor measurements
Outdoor measurements will be among the most accessible to many, and
if successful, will be very useful for convincing skeptics without more
rigorous lab testing available.
eventually a necessity
Not very useful scientifically, but nice for demonstration issues
Difficult to use as a standard.
The relevance of test procedures should be verified using outdoor
exposure.
Extermely important to strat with field tests as soon as possible,
offcourse depending on the robustness of the system.
Only after can survive 100 hours of 85% RH/ 85 C.
Encapsulation Measurement Techniques
ellipsometry
Need another rapid meaniful technique that to my knowledge has not
been identified yet.
I have yet to see "stabilized identical devices" in organic PV. Most of
differences in organic PV efficiency may not revealed by "round robin"
since the biggest issue seems to be what do you call the area and was an
aperture used. If round robin on identical devices is to be conducted lets
do one with stable filtered Si reference cells.
Comments for the organizers for the meeting
This is a lot to address in two days (especially if there are close to 100
different opinions at the beginning).
None
Having a database already on hand, with early entries, would facilitate
discussion. That might be difficult to get done in time...

try to invite some people from the fields of lifetime testing x-Si PV and
organic LED
Have you arranged for someone to show up with existing standards that
were developed for a-Si and other technologies? Why should you create
new standards? Why not use existing standards?
In my view there are different separate topics to discuss
- intrinsic stability issues: do we need fundamental understandig of the
degradation mechanisms. How can we do this most efficiently? Maybe
invite somebody from the polyLED/Lighting field who has experience with
this.
- Extrinisc issues: packaging, what are requirements for which
application
- Development of IEC type of standards: For this discussion the
photoactive layer itself is not that important. This should be a more
general discussion. We should talk about development of tests that are
specific for a certain product (flexible vs. rigid) or for specific type of
applications (low power, mdeium power, highpower). It is good to invite
peole who are allready commercializing flexible inorganic PV for charging
applications for instance and how they deal with test standards which are
not existing yet. And invite people from certification labs (for instance
ISE, NREL, TUV, etc) who knows what is needed to come to
standardatization.
stability / lifetime testing is difficult, time consuming and receives only
little attention. In the end it is as important as obtaining high efficiencies.
However, typically, stability papers claiming record values do not receive
as much attention as papers claiming record efficiencies. This is just to
indicate that research in stability does not receive the attention as it
deserves. Perhaps a conserted action could help.
A special session on OPV stability at the E-MRS might be a good idea,
similarly at a US conference. However, an update once a year should be
sufficient.
A two track long term research programme on generating (intrinsic and
extrinsic) stability data using measurement protocols could serve a trial
and error method to improve stability. In a different track one could build
up a knowledge base on chem. structure-property&morphology-stability
relation. Hopefully leading to a scientific understanding of processes
influencing device lifetime.
Perhaps a conserted action among institutes/universities/companies
could help to us the limited resources efficiently.
Perhaps Michael Köhl from Fraunhofer could give valuable input from
testing protocols. Also strengthening the relations with other organic

electronic communities maybe helpful.
What would be the killer applications for OPV
Viable Packaging Options
No entirely my field. I think that imprtant questions still exist, even if
encapsulation would be perfect. My largest concern is the long-term
stability of the morphology and the integretity of the layer stack and its
interfaces.
I think we should develop OPVs that do not need
encapsulation/protection against oxygen/water
Thin glass should not be ignored for early implementation.
glass
I think you need to understand the degradation mechanisms and
engineer around them rather than trying to solve the problems with
encapsulation. The encapsulation should give physical protection and
protection from puddles of water, but the devices should be able to
survive small exposures.
The packaging will depend on the application
Don't count on the package to solve stability issues. Cells that degrade
in seconds in air can not be made stable by low cost low temperature
package solutions. At present glass / glass packaging on option that has
a chance of protection.
OPV cells sealed with glass may be used as standard reference device