Dear/ Colleagues,
I hope everything is going well with you. I fabricated some OPV devices with inverted geometry employing the structure
ITO/ZnO/P3HT: PC70BM/ MoO3(8 nm)/Ag(100 nm). However, the PCEs of such devices were in the range between approximately 0.7% to 0.9 %. The common observation about those devices is the low value of open circuit voltage ranging from 380 to 420 mV.
I attached the I-V curve for one of the devices. Here are the photovoltaic parameters:-
Jsc = -4.68 mA/cm2 .... Voc= 0.387 V
F.F.= 0.38 ..... PCE = 0.68%.
Please note that:-
1- ZnO sol-gel was prepared by dissolving 0.109 gm of zinc acetate in 1 ml of 2-methoxyethanol and adding 32 microliters of ethanolamine. Then, the spin-coated films were annealed at (170-190 oC) for 45 minutes.
2- The active layer was annealed for 10 minutes at 80 oC for some devices and at 120 oC for other devices.
3- Devices were not annealed after compleate fabrication.
Could you please suggest some reasons for the low Voc and FF or how to find out such limiting factors?
Best regards,
Michael
Dear Michael Kamel ,
Your solar cell structure may have the following deficiencies:
The short circuit current is relatively low for the AM1.5 illumination.
This means that either the generation and collection of the charge carriers is lower than it should be.
The other deficiency is the low open circuit voltage. This is due to use of not matched ETL and HTL.
I think this is the main cause of the bad performance of the soalr cells.
It is clear that your fill factor is relatively low because of the relatively high series resistance.
You have also partial shorts may be because of the pin holes.
If you studied the analytical models and the numerical simulations you will get an insight in these structures which help you to build and test such cells.
Therefor I would like that you see the papers:Conference Paper Generic Analytical Models for Organic and Perovskite Solar Cells
Article Possible efficiency boosting of non-fullerene acceptor solar...
You can also display the dark characteristics to show the behavior of the soar cells under darkness. Your device will show high ohmic performance.
Best wishes
First, I assume you're using sunlight, or something similar to sunlight eg Xe arc or W-halide lamp. The low Isc indicates only about 10% of photons are being converted into useful electrons. Where are the remainder going? Second, the low Voc shows a high voltage drop inside the cell, This can be due to high internal resistance or high overvoltage in one of the internal electron or hole transitions. But few OPVs do a lot better than yours, so don't be discouraged!
Dear Tony Maine Thanks for your comment. I use solar simulator for this measurement. In your opinion what is the expected value for short circuit current density? By the way, I have seen similar values to mine in literature. However, the open circuit voltage and F.F are higher than my values. Do you think, the thickness of ZnO and/or the active layer can be a reason?
regards,
Michael
Dear Michael Kamel ,
Your solar cell structure may have the following deficiencies:
The short circuit current is relatively low for the AM1.5 illumination.
This means that either the generation and collection of the charge carriers is lower than it should be.
The other deficiency is the low open circuit voltage. This is due to use of not matched ETL and HTL.
I think this is the main cause of the bad performance of the soalr cells.
It is clear that your fill factor is relatively low because of the relatively high series resistance.
You have also partial shorts may be because of the pin holes.
If you studied the analytical models and the numerical simulations you will get an insight in these structures which help you to build and test such cells.
Therefor I would like that you see the papers:Conference Paper Generic Analytical Models for Organic and Perovskite Solar Cells
Article Possible efficiency boosting of non-fullerene acceptor solar...
You can also display the dark characteristics to show the behavior of the soar cells under darkness. Your device will show high ohmic performance.
Best wishes
Dear Prof. Abdelhalim abdelnaby Zekry
Thanks so much for your continuous support. I'm always happy with your comments and discussion. However, I am not in total agreement with you this time. Compared to literature, the value of short circuit current density of my device is quite acceptable, but the VOC should be higher (typically around 0.6 V). In addition, this particular structure was used by different research groups and PCEs exceeding 3.5% were recorded. Therefore, the selection of both buffer layers (ETL and HTL) is appropriate.
Regarding probable shorting within the device layers, proper filters were used just before spin coating to avoid this issue.
The dark J-V measurement showed a good diode behavior (exponential function).
Finally, do you believe that device degradation can be the reason? especially because the device is not encapsulated. But, please note that this measurement was performed just after the deposition of Ag electrode.
All the best,
Michael
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