The Ossila Scharber Calculator
The Ossila efficiency calculator designed to allow you to estimate what efficiencies ought to be possible from a material combination based upon their HOMO and LUMO levels. It is based upon the Scharber model[1] which has been shown to be an effective starting point for materials evaluation.
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Notes
We hope you find this model useful. As with all models, caution should be used when analysing results, however, as a rough guide we have found this model to be very useful for seeing whether a certain material combination is worth investigating.
Actual performance will of course depend upon much more that the HOMO and LUMO levels, however this model is intended a simple tool to calculate the maximum efficiencies that could be achieved with good phase-seperation on the correct length scales as well as efficient charge separation and extraction.
Regarding the assumption for fill factor and EQE, which are required in order to estimate efficiency, "65/65 rule" of 65% fill factor and 65% EQE is often a good starting point. While fill factors in excess of 70% and EQE's in excess of 80% have been achieved for certain materials these values are hard to get in combination and for many materials this would be impossible. As such 65/65 is a moderate assumption for a material combination with good charge transport and correct phase seperation.
Bear in mind that there is of often a lot of discrepancy in the literature with regards to HOMO and LUMO values from cyclic voltammetry and often the Eg is defined by the optical bandgap as opposed to the cyclic voltammetry data. While data measured in the same lab is usually excellent for comparison, data from different labs can be offset by up to 0.3 eV.
In some cases this model can give an underestimate for efficiency, for example with P3HT/PCBM cells the vibronic absorption shoulder is not included in the model and the average EQE achieved can actually be higher than 65%. In many cases though it will be an overestimate, as for example with PCPDTBT/PCBM where there can be difficulties with charge dissociation which generally limit fill factors.
If you have any comments or suggestions for improvements that can be made please don't hesitate to contact us.
[1] "Design Rules for Donors in Bulk-Heterojunction Solar Cells - Towards 10% Energy-Conversion Efficiency," Markus C. Scharber, David Muhlbacher, Markus Koppe, Patrick Denk, Christoph Waldauf, Alan J. Heeger, and Christoph J. Brabec, Advanced Materials, 18, 789, (2006).
