How do you find the answer below on the given question:
Why does the fill factor not go beyond 47% in inverted structure polymer solar cells devices (P3HT:PC60BM)?
all the improvement i have done could increase the Voc and Jsc up to 62V and 13mA/cm2, respectively, but FF hasn't changed much.
in the link:https://www.researchgate.net/post/Why_does_the_fill_factor_not_go_beyond_47_in_inverted_structure_polymer_solar_cells_devices_P3HTPC60BM#view=548aeeaad685cc267a8b4673
The answer:
Dear Tahmineh Mahmoudi
Please allow me to share in your discussion about the fill factor of the solar cells. The fill factor is defined by FF= Pm/ (Voc Isc), where Pm is the maximum output power, Voc is the open circuit voltage and Isc is the shortcircuit current. It is a measure of the squareness of the I-V characteristics of the solar cell. The factors affecting the fill factors are:
- The series resistance of the solar cell,Rs
-The parallel resistance of the solar cell .Rsh
-The ideality factor n of the dark current of the cell evaluated as a diode.
The series resistance is composed of the resistance of the different semiconductor layers of the cell in addition to the metal semiconductor contacts,the MS contacts.Because your structure is a thin film polymer structure,its layer resistance may be relatively high. But the much more serious may be the MS contact resistance as it may be large and nonlinear acting as a Schottky diode
This effect is demonstratively seen in the paper titled:Interface engineering of stable, efficient polymer solar cells, given in the Link:http://spie.org/x35266.xml
-The shunt resistance arises because of the leakage across the junction.
- the recombination rate is normally high in such materials because of the Langevin recombination mechanism since if the photogenerated electron hole pairs are not extracted from the polymer at the right time, they will recombine again. This acts as if there is large recombination centers in the material. As a consequence, it could increase the ideality factor beyond the nominal value of n= 1-2. and consequently reduces the squareness of the I-V characteristics and the FF.
-AS the reverse saturation current decreases the squareness of the I-V curve is enhanced and consequently the FF increases.
So, you it is advisable to measure these parameters in order to explore the observed value of the FF of your cells. I don not think that you have errors in the results if i compare your result with that given in the link they are okay.
It is the matter of enhancing the charge transfer rate from the polymer and across their metal interfaces.
The maximum FF is achieved with:
Rs=zero,
Rsh= infinity,
and the ideality factor=1.
For more details see the paper: A. Zekry and G. El-Dllal, “effect of the MS contact on the electrical behavior of solar cells”, Journal of solid-state Electronics, Vol.31, No.1, 1988.,1.48 Impact Factor
I hope i shed some light on the relatively low value low of the FF of your cells. This is my own vision to this phenomenon.
wish you success
Thank you
To support my answer i found this phd on the such cells:
https://stacks.stanford.edu/file/druid:qj736sk9775/Thesis%20Shanbin%20online%20submission%20March%202010%20version-augmented.pdf
The fill factor increases with decreasing ideality factor, with decreasing series resistance, and increasing open circuit voltage of the solar cell. For ideal factor = 1, series resistance = 0, one can easily calculate the theoretical maximum fill factor, which can be 0.47, if the open circuit voltage is that low. The ideal fill factor certainly should be higher than 0.47, if the open circuit voltage is 0.62 V.
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