Interplay between Strong Coupling and Radiative Damping of Excitons and Surface Plasmon Polaritons in Hybrid Nanostructures

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Coherent ultrafast charge transfer in an organic photovoltaic blend

Blends of conjugated polymers and fullerene derivatives are prototype systems for organic photovoltaic devices. The primary charge-generation mechanism involves a light-induced ultrafast electron transfer from the light-absorbing and electron-donating polymer to the fullerene electron acceptor. Here, we elucidate the initial quantum dynamics of this process. Experimentally, we observed coherent vibrational motion of the fullerene moiety after impulsive optical excitation of the polymer donor. Comparison with first-principle theoretical simulations evidences coherent electron transfer between donor and acceptor and oscillations of the transferred charge with a 25-femtosecond period matching that of the observed vibrational modes. Our results show that coherent vibronic coupling between electronic and nuclear degrees of freedom is of key importance in triggering charge delocalization and transfer in a noncovalently bound reference system

Tracking the coherent generation of polaron pairs in conjugated polymers

The optical excitation of organic semiconductors not only generates charge-neutral electron-hole pairs (excitons), but also charge-separated polaron pairs with high yield. The microscopic mechanisms underlying this charge separation have been debated for many years. Here we use ultrafast two-dimensional electronic spectroscopy to study the dynamics of polaron pair formation in a prototypical polymer thin film on a sub-20-fs time scale. We observe multi-period peak oscillations persisting for up to about 1 ps as distinct signatures of vibronic quantum coherence at room temperature. The measured two-dimensional spectra show pronounced peak splittings revealing that the elementary optical excitations of this polymer are hybridized exciton-polaron-pairs, strongly coupled to a dominant underdamped vibrational mode. Coherent vibronic coupling induces ultrafast polaron pair formation, accelerates the charge separation dynamics and makes it insensitive to disorder. These findings open up new perspectives for tailoring light-to-current conversion in organic materials

The state of adolescent menstrual health in low- and middle-income countries and suggestions for future action and research

In recognition of the opportunity created by the increasing attention to menstrual health at global, regional, and national levels, the World Health Organization’s Department of Sexual and Reproductive Health and Research and the UNDP-UNFPA-UNICEF-WHO-World Bank Special Programme of Research, Development and Research Training in Human Reproduction convened a global research collaborative meeting on menstrual health in adolescents in August 2018. Experts considered nine domains of menstrual health (awareness and understanding; stigma, norms, and socio-cultural practices; menstrual products; water and sanitation; disposal; empathy and support; clinical care; integration with other programmes; and financing) and answered the following five questions: (1) What is the current situation? (2) What are the factors contributing to this situation? (3) What should the status of this domain of adolescent menstrual health be in 10 years? (4) What actions are needed to achieve these goals? (5) What research is needed to achieve these goals? This commentary summarizes the consensus reached in relation to these questions during the expert consultation. In doing so, it describes the state of adolescent menstrual health in low- and middle-income countries and sets out suggestions for action and research that could contribute to meeting the holistic menstrual health needs of adolescent girls and others who menstruate worldwide

Two-dimensional electronic spectroscopy reveals ultrafast dynamics at a conical intersection in an organic photovoltaic material

Two-dimensional electronic spectroscopy with sub-10-fs time resolution reveals signatures of vibronic coupling and wavepacket motion through a conical intersection in the initial charge separation dynamics of an acceptor-donor-acceptor oligomer thin film for organic solar cells

Ultrafast relaxation dynamics in a polymer: fullerene blend for organic photovoltaics probed by two-dimensional electronic spectroscopy

Ultrafast charge transfer from a photoexcited donor to an acceptor moiety is at the heart of the energy conversion in organic photovoltaics (OPVs). Efficient charge transfer on ultrafast, sub-100-fs timescales has been reported in many OPV materials. Yet at present, the elementary mechanisms underlying this process in OPV materials, in particular the role of coupled electronic and nuclear motion for the transfer dynamics and yield, are still unclear. Here, we use ultrafast two-dimensional electronic spectroscopy (2DES) to investigate vibronic couplings in the initial, light-induced charge separation dynamics in a blend of poly-3-hexyl-thiophene (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM), a prototypical OPV system. At early times, we observe a distinct breakup of the unstructured linear spectrum into a series of well-resolved vibronic resonances. A comparison to 2DES spectra of pure P3HT suggests that these resonances arise from the vibronic coupling between donor states of the polymer and charge-separated states involving the PCBM acceptors. We identify new, short-lived diagonal peaks, decaying substantially within only about 20–30 fs and lacking a well-resolved cross-peak structure. We argue that these unexpected dynamics likely arise from strong anharmonic couplings to several vibrational modes. One possibility to explain the rapid decay of the blend peaks would be passing of the photoexcited wavepacket through a conical intersection. Our results suggest that nonadiabatic dynamics on multidimensional potential energy surfaces (PESs) might be highly relevant for the initial steps of light-induced charge separation in organic materials. Since theoretical investigations of vibronically-assisted dynamics in such complex organic systems are just emerging, we hope that our results will stimulate further experimental and theoretical work on the role of such dynamics in artificial energy conversion materials. To this end, coherent multidimensional spectroscopy might be a key experimental tool

Coherent ultrafast charge transfer in an organic photovoltaic blend

Combining high-time resolution pump-probe spectroscopy and timedependent density functional theory calculations, we show that coherent vibroniccoupling is of key importance in triggering charge transfer in a technologically relevant organic photovoltaic blend

Intermolecular conical intersections in molecular aggregates

Conical intersections (CoIns) of multidimensional potential energy surfaces are ubiquitous in nature and control pathways and yields of many photo-initiated intramolecular processes. Such topologies can be potentially involved in the energy transport in aggregated molecules or polymers but are yet to be uncovered. Here, using ultrafast two-dimensional electronic spectroscopy (2DES), we reveal the existence of intermolecular CoIns in molecular aggregates relevant for photovoltaics. Ultrafast, sub-10-fs 2DES tracks the coherent motion of a vibrational wave packet on an optically bright state and its abrupt transition into a dark state via a CoIn after only 40 fs. Non-adiabatic dynamics simulations identify an intermolecular CoIn as the source of these unusual dynamics. Our results indicate that intermolecular CoIns may effectively steer energy pathways in functional nanostructures for optoelectronics.Fil: De Sio, Antonietta. Carl von Ossietzky Universität Oldenburg; AlemaniaFil: Sommer, Ephraim. Carl von Ossietzky Universität Oldenburg; AlemaniaFil: Nguyen, Xuan Trung. Carl von Ossietzky Universität Oldenburg; AlemaniaFil: Groß, Lynn. Universitat Bremen; AlemaniaFil: Popović, Duško. Universitat Ulm; AlemaniaFil: Nebgen, Benjamin Tyler. Los Alamos National Laboratory; Estados UnidosFil: Fernández Alberti, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; ArgentinaFil: Pittalis, Stefano. Consiglio Nazionale delle Ricerche; ItaliaFil: Rozzi, Carlo Andrea. Consiglio Nazionale delle Ricerche; ItaliaFil: Molinari, Elisa. Consiglio Nazionale delle Ricerche; Italia. Università di Modena e Reggio Emilia; ItaliaFil: Mena Osteritz, Elena. Universitat Ulm; AlemaniaFil: Bäuerle, Peter. Universitat Ulm; AlemaniaFil: Frauenheim, Thomas. Universitat Bremen; Alemania. Shenzhen JL Computational Science And Applied Research Institute; ChinaFil: Tretiak, Sergei. Los Alamos National Laboratory; Estados UnidosFil: Lienau, Christoph. Carl von Ossietzky Universität; Alemani