Periodic Reporting for period 2 - QuESt (Quantum Enhanced Organic Photovoltaics by Strong Coupling of IR Vibrations to an Optical Cavity)
Periodo di rendicontazione: 2020-09-01 al 2021-08-31
The central aim of QuESt is to understand how the efficiency of materials used in organic photovoltaics (OPV) that convert sunlight into free charges can be enhanced by the emerging approach of modifying material properties by strong light-matter coupling. Under strong light-matter coupling, which can be achieved for example by placing molecules in an optical cavity which is essentially a pair of mirrors that trap light within them, new hybrid (part-molecule part-light) states called polaritons are formed, which behave very differently than its constituent parts.
Organic photovoltaics that are based on organic molecules, offer an attractive alternative to conventional solar cells due to their advantages such as optical tunability, lightweight, and design flexibility. However, their overall efficiencies in converting sunlight into free charges (and hence electricity) is still limited. In recent years, the potential to modify the physical properties of materials and molecules by making it interact with an optical cavity mode in the strong coupling regime has been recognized and experimentally demonstrated.
In QuEst we aim to provide guidelines on how strongly coupling the vibrational modes of materials used in OPVs with the modes of an optical cavity can modify the rate at which the material converts light into free charges. We aim to develop physical models to predict i) the energy structure, for example, what are the new energies at which hybrid states absorb and emit light, ii) the dynamics and iii) the optical response (spectra), of strongly coupled systems, and benchmark these with ultrafast spectroscopy experiments.
The success of this action will not only benefit the scientific community working on OPVs but importantly will advance our knowledge on the general and relatively new field of modifying the properties of molecular systems by strong light-matter coupling.
Organic photovoltaics that are based on organic molecules, offer an attractive alternative to conventional solar cells due to their advantages such as optical tunability, lightweight, and design flexibility. However, their overall efficiencies in converting sunlight into free charges (and hence electricity) is still limited. In recent years, the potential to modify the physical properties of materials and molecules by making it interact with an optical cavity mode in the strong coupling regime has been recognized and experimentally demonstrated.
In QuEst we aim to provide guidelines on how strongly coupling the vibrational modes of materials used in OPVs with the modes of an optical cavity can modify the rate at which the material converts light into free charges. We aim to develop physical models to predict i) the energy structure, for example, what are the new energies at which hybrid states absorb and emit light, ii) the dynamics and iii) the optical response (spectra), of strongly coupled systems, and benchmark these with ultrafast spectroscopy experiments.
The success of this action will not only benefit the scientific community working on OPVs but importantly will advance our knowledge on the general and relatively new field of modifying the properties of molecular systems by strong light-matter coupling.
The work performed and results obtained in QuESt are the following:
1. Development of the theoretical framework to describe the collective coupling of molecules to an optical cavity mode that allowed the calculation of the energy structure and dynamics of coupled systems and how they relate to the observed non-linear response in optical experiments such as transient absorption. This was specifically applied to an ensemble of strongly coupled molecules (4CzIPN) (work published on J. Phys. Chem. Lett. 2020). A general perspective that discussed the possibilities enabled by placing many molecules in optical cavities that interact with the same mode of the electromagnetic field, with a focus on the collective behavior and delocalization of polaritons, similar to molecular excitons, and the ultrafast photophysics that can be explored by non-linear spectroscopies was produced and published in J. Phys. Chem. Lett in 2021.
2. Theoretical interpretation of the charge transfer mechanism in materials relevant to organic photovoltaics investigated by pump-push-probe. This work provides new insights into the microscopic origin that allows efficient charge separation in organic materials for OPVs. Work is ready for submission for publication in peer reviewed journal.
3. Investigation on the entanglement properties of molecular polaritons. In this direction, a proposal to measure exciton entanglement (here understood as delocalization) through linear spectroscopy was carried out (published in PRA in 2021) and the extension to polaritons is in progress.
4. Complementary to the scientific activities strictly related to the core of the project, and within the broader field of utilizing quantum phenomena to modify function in molecular systems, investigations on excited state intramolecular proton transfer (ESIPT) were carried out. In this context, the fellow supervised a PhD student working on the theoretical aspects of the project to develop an open quantum systems approach to treat ESIPT and analyze the role of quantum coherence. In particular, in a combined experimental and theoretical work, it was proposed that quantum interference may explain unconventional isotope effects in two-site excited state intramolecular proton transfer revealed by experiments performed in the group of Prof. Scholes (Princeton). This work was published in PNAS in 2021.
5. Also in the context of mentoring a PhD student (as in #4), studies of intramolecular proton transfer in single-site molecules and the associated ultrafast optical response were carried out. The aim was to clarify what is the microscopic mechanism behind the ultrafast ESIPT mechanism which is a matter still under debate. This work was published in 2022 in ACS Physical Chemistry Au.
In addition to the dissemination of the work in scientific journals, outreach activities toward the general public were carried out:
[1] Article in local newspaper Il Piccolo, highlighted on SISSA social media https://www.facebook.com/SISSAschool/posts/an-article-dedicated-to-physicist-francesca-fassioli-olsen-was-published-in-il-p/1646262625419306/
[2] 'Lightweight, bendy, cheaper' – the promise of organic solar panels', article in Horizon Magazine
[3] 'Le donne nella città della scienza', participation in exhibition on female scientists in the city of Trieste
1. Development of the theoretical framework to describe the collective coupling of molecules to an optical cavity mode that allowed the calculation of the energy structure and dynamics of coupled systems and how they relate to the observed non-linear response in optical experiments such as transient absorption. This was specifically applied to an ensemble of strongly coupled molecules (4CzIPN) (work published on J. Phys. Chem. Lett. 2020). A general perspective that discussed the possibilities enabled by placing many molecules in optical cavities that interact with the same mode of the electromagnetic field, with a focus on the collective behavior and delocalization of polaritons, similar to molecular excitons, and the ultrafast photophysics that can be explored by non-linear spectroscopies was produced and published in J. Phys. Chem. Lett in 2021.
2. Theoretical interpretation of the charge transfer mechanism in materials relevant to organic photovoltaics investigated by pump-push-probe. This work provides new insights into the microscopic origin that allows efficient charge separation in organic materials for OPVs. Work is ready for submission for publication in peer reviewed journal.
3. Investigation on the entanglement properties of molecular polaritons. In this direction, a proposal to measure exciton entanglement (here understood as delocalization) through linear spectroscopy was carried out (published in PRA in 2021) and the extension to polaritons is in progress.
4. Complementary to the scientific activities strictly related to the core of the project, and within the broader field of utilizing quantum phenomena to modify function in molecular systems, investigations on excited state intramolecular proton transfer (ESIPT) were carried out. In this context, the fellow supervised a PhD student working on the theoretical aspects of the project to develop an open quantum systems approach to treat ESIPT and analyze the role of quantum coherence. In particular, in a combined experimental and theoretical work, it was proposed that quantum interference may explain unconventional isotope effects in two-site excited state intramolecular proton transfer revealed by experiments performed in the group of Prof. Scholes (Princeton). This work was published in PNAS in 2021.
5. Also in the context of mentoring a PhD student (as in #4), studies of intramolecular proton transfer in single-site molecules and the associated ultrafast optical response were carried out. The aim was to clarify what is the microscopic mechanism behind the ultrafast ESIPT mechanism which is a matter still under debate. This work was published in 2022 in ACS Physical Chemistry Au.
In addition to the dissemination of the work in scientific journals, outreach activities toward the general public were carried out:
[1] Article in local newspaper Il Piccolo, highlighted on SISSA social media https://www.facebook.com/SISSAschool/posts/an-article-dedicated-to-physicist-francesca-fassioli-olsen-was-published-in-il-p/1646262625419306/
[2] 'Lightweight, bendy, cheaper' – the promise of organic solar panels', article in Horizon Magazine
[3] 'Le donne nella città della scienza', participation in exhibition on female scientists in the city of Trieste
QuESt made significant contributions towards the state of the art with possible implications to the larger of society:
1. The theoretical analysis of ultrafast non-linear spectra of strongly coupled molecules in terms of transitions from one to two particle states had not been properly analyzed in the scientific community and therefore represents an important contribution beyond the state of the art.
2. Proposal to detect exciton entanglement through spectroscopy is novel and represents an interesting alternative to detecting quantum phenomena directly from spectra (this work was chosen as EDitor's suggestion in PRA)
3. Studies on materials relevant for OPVS and how their efficiency is or can be controlled contributes towards solving the energy problem relevant to society.
4. Studies on intramolecular excited state proton transfer, specially the work on how quantum interference may be at play in modifying reaction rates, contributes towards the aim of using quantum mechanics to enhance function which is at the center of quantum technologies.
5. Overall the progress made by QuEST in understanding how molecules hybridize with light under strong coupling brings us a step closer to being able to utilize strong coupling in applications, which is again relevant to the field of quantum technologies.
1. The theoretical analysis of ultrafast non-linear spectra of strongly coupled molecules in terms of transitions from one to two particle states had not been properly analyzed in the scientific community and therefore represents an important contribution beyond the state of the art.
2. Proposal to detect exciton entanglement through spectroscopy is novel and represents an interesting alternative to detecting quantum phenomena directly from spectra (this work was chosen as EDitor's suggestion in PRA)
3. Studies on materials relevant for OPVS and how their efficiency is or can be controlled contributes towards solving the energy problem relevant to society.
4. Studies on intramolecular excited state proton transfer, specially the work on how quantum interference may be at play in modifying reaction rates, contributes towards the aim of using quantum mechanics to enhance function which is at the center of quantum technologies.
5. Overall the progress made by QuEST in understanding how molecules hybridize with light under strong coupling brings us a step closer to being able to utilize strong coupling in applications, which is again relevant to the field of quantum technologies.