Short-Term Metal/Organic Interface Stability Investigations of Organic Photovoltaic Devices: Preprint Page: 4 of 6
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Fig. 1: Samples exposed to air (in the dark) for up to 100 min. The devices, as well as the organic surface are remarkably
stable over this timescale. The starting efficiencies for all devices, to which all data is normalized, were roughly 4%.RESULTS AND DISCUSSION
Dark, Delayed Contact Experiment
A summary of device performance for the dark set of
experiments is presented in Figure 1. As can be seen, there
is no substantial difference between the original or delayed set
of devices on each sample exposed to air from zero to ten
minutes. For 100 minutes of air exposure, however, there ap-
pears to be a little degradation. Measurements were made
after exposure to air both before and after the second deposi-
tion, to see if the extra vacuum step associated with evapora-
tion might reverse some portion of any observed damage. It
is not clear that there was any real effect, from this on the
original set of devices.
Here, the greatest reduction in efficiency comes in
the short circuit current density (Js3). Larger Jsc variations were
noted in this study, than previously for devices kept in a
glovebox under partial illumination for ten days.[4] Across all
of the samples, the open circuit voltage (Vo,) is the most ro-
bust of the critical parameters remaining relatively constant
even for devices with delayed contacts. In the previous study,
while there was no completely analogous measurement, a Vo
reduction of -4% was observed for devices illuminated at one
sun for 10% of the time (over a ten day period), and -2% re-
duction for their siblings with delayed contacts.[4]
One Sun Illumination, Delayed Contact Experiments
A summary of device performance for the constant
one sun illumination set of experiments is presented in Figure2. As can be seen, 150 min. of constant exposure to light
(and somewhat elevated temperature) in an inert environment
caused more degradation than 100 min. in air, in the dark. In
fact, 150 min of light exposure in a glovebox, caused more
degradation than either 5 or 25 min. constant illumination in air
to the original set of devices. The original devices from the
glovebox sample performed very similarly to the original de-
vices from the sample with 100 min. of air and light exposure.
While illumination in or out of a glovebox causes
some degradation, the glovebox apparently protects the or-
ganic surface from significant degradation when illuminated as
seen in the relative performance of the delayed contact de-
vices for the 25 and 100 min. samples.
In this set of experiments, the extra vacuum step
again had no significant effect on the devices' overall per-
formance. The greatest reduction in overall performance
again comes from changes in Js, this time with 28% and 65%
drops relative to the original baseline devices for 25 min. and
100 min. exposures to air and light.
In the previous study, an almost 10% reduction in Von
was observed after ten days of constant illumination in a
glovebox for the original set of devices and about a 4% reduc-
tion for delayed contacts.[4] Here, there is at most a few per-
cent permanent degradation in Vo0, with the extra vacuum
step's reviving the devices' Vo.
In the previous study, after ten days the delayed con-
tact devices exposed to constant illumination and air were
dead, while the (unencapsulated) original set had degraded
less than 50% of its original value.[4] Here, we can see that
the kinetics for total organic surface degradation in air are on
the timescale of maybe a few hours when exposed to one sun
(and somewhat elevated temperature).2
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Reese, M. O.; Morfa, A. J.; White, M. S.; Kopidakis, N.; Shaheen, S. E.; Rumbles, G. et al. Short-Term Metal/Organic Interface Stability Investigations of Organic Photovoltaic Devices: Preprint, article, May 1, 2008; Golden, Colorado. (https://digital.library.unt.edu/ark:/67531/metadc898859/m1/4/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.