Dear people,
I am confused about LUMO orbitals in photovoltaic solar cells. According to the literature, Voc (open circuit voltage) is related to the HOMO orbital of donor and LUMO orbital of acceptor. My question is that the charge transfer takes place exactly from the HOMO orbital of donor to the LUMO orbital of acceptor or maybe the LUMO+1 and upper one. What about the situation that TDDFT calculation shows that electron excitation from HOMO to LUMO of acceptor is forbidden and electron excitation occur from HOMO to LUMO+n orbitals?
Regards,
Bahareh Bamdad
Dear Bahareh Bamdad
welcome!
It is so that the incident photons with the proper energy produce excitons which are bound electron hole pairs because of they electrostatically attract each other.
This happens in the donor absorber layer. The excitons diffuse to the interface between the donor - acceptor interface where the acceptor molecules capture the electrons and separate them from their excitons. The holes of the excitons are derived back to the hole transport layer and the electrons are derived by the built in electric field to the ETL. On their separation the excitons loose an energy equal to the difference between the the Luno level of the donor and the lumo level of the acceptor. It means that after separation of the electrons hole pairs they will have only a potential energy= Eld-Eha.
For more information please follow the paper: Conference Paper Generic Analytical Models for Organic and Perovskite Solar Cells
Best wishes
Hi there,
typically, the idea is that the charge transport is mediated through the aptly named charge transfer (CT) state and not directly from the donor HOMO to the acceptor LUMO, although that is sometimes portrayed. A good overview of how the charges in a solar cell are generated, and then separated into free charge carriers can be found in this paper: Article The binding energy and dynamics of charge-transfer states in...
Specifically Figure 6 of that paper gives a good overview of the different states that might be involved in the charge separation. But keep in mind that this is still only a model and that reality is likely even more complex.
Best regards,
Joachim
Dear Bahareh Bamdad
welcome!
It is so that the incident photons with the proper energy produce excitons which are bound electron hole pairs because of they electrostatically attract each other.
This happens in the donor absorber layer. The excitons diffuse to the interface between the donor - acceptor interface where the acceptor molecules capture the electrons and separate them from their excitons. The holes of the excitons are derived back to the hole transport layer and the electrons are derived by the built in electric field to the ETL. On their separation the excitons loose an energy equal to the difference between the the Luno level of the donor and the lumo level of the acceptor. It means that after separation of the electrons hole pairs they will have only a potential energy= Eld-Eha.
For more information please follow the paper: Conference Paper Generic Analytical Models for Organic and Perovskite Solar Cells
Best wishes
This page and the references cited in, may help
https://link.springer.com/chapter/10.1007/978-3-319-48933-9_54
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