Electronic Structure of Isolated Graphene Nanoribbons in Solution Revealed by Two-Dimensional Electronic Spectroscopy

Structurally well-defined graphene nanoribbons (GNRs) are nanostructures with unique optoelectronic properties. In the liquid phase, strong aggregation typically hampers the assessment of their intrinsic properties. Recently we reported a novel type of GNRs, decorated with aliphatic side chains, yielding dispersions consisting mostly of isolated GNRs. Here we employ two-dimensional electronic spectroscopy to unravel the optical properties of isolated GNRs and disentangle the transitions underlying their broad and rather featureless absorption band. We observe that vibronic coupling, typically neglected in modeling, plays a dominant role in the optical properties of GNRs. Moreover, a strong environmental effect is revealed by a large inhomogeneous broadening of the electronic transitions. Finally, we also show that the photoexcited bright state decays, on the 150 fs time scale, to a dark state which is in thermal equilibrium with the bright state, that remains responsible for the emission on nanosecond time scales

Instantaneous charge separation in non-fullerene acceptor bulk-heterojunction of highly efficient solar cells

Using broadband transient absorption in a high efficiency (>11%) photovoltaic blend with a non-fullerene acceptor, we observe instantaneous (sub-30 fs) charge separation, demonstrating close to ideal donor-acceptor level matching and nanomorphology in this blend

Instantaneous charge separation in non-fullerene acceptor bulk-heterojunction of highly efficient solar cells

Using broadband transient absorption in a high efficiency (>11%) photovoltaic blend with a non-fullerene acceptor, we observe instantaneous (sub-30 fs) charge separation, demonstrating close to ideal donor-acceptor level matching and nanomorphology in this blend

Two-dimensional electronic spectroscopy of graphene nanoribbons in organic solution

We unravel the electronic structure of graphene nanoribbons in solution using two-dimensional electronic spectroscopy. We identify different excitons, their vibrational couplings and find that exciton diffusion or relaxation among the exiton sublevels takes place in ~300 fs

Two-dimensional electronic spectroscopy of graphene nanoribbons in organic solution

We unravel the electronic structure of graphene nanoribbons in solution using two-dimensional electronic spectroscopy. We identify different excitons, their vibrational couplings and find that exciton diffusion or relaxation among the exiton sublevels takes place in ~300 fs

Ultrafast carrier interactions in metal-halide perovskites probed with two-dimensional electronic spectroscopy

We use 2D electronic spectroscopy with sub-10-fs resolution to probe carrier-carrier scattering in perovskites. We report excitation-density dependent thermalization times below 100-fs. Strong coupling with excitonic states further reveals sub-bandgap states with low oscillator strength