Exciton Dissociation and Electron Transfer at a Well-Defined Organic Interface of an Epitaxial C₆₀ Layer on a Pentacene Single Crystal

Abstract

The electron transfer of a well-defined singlecrystalline organic P−N interface of the epitaxial layer of C 60 on the surface of a single-crystalline pentacene (Pen-SC) was observed using time-resolved photoemission electron microscopy (TR-PEEM) with an optical pump and probe mode. The fine energytuning of the probe light and the selected-area detection of the photoelectrons, in addition to the PEEM detection of photoelectrons, allowed the measurement of the dynamics of electrons of rather insulating organic interfaces with a high signal-to-noise ratio, without suffering from the charging of the sample. After determination of the relaxation of the photogenerated electrons in Pen-SC via singlet fission through multiple-exciton states, two distinct electron transfer processes to the LUMO of the C 60 layer were clearly observed by direct detection of the time evolution of the electrons in the LUMO of C 60 .

Photoelectron spectroscopy on single crystals of organic semiconductors: experimental electronic band structure for optoelectronic properties

“…34(c)] also represented an absence of strong electronic coupling between C 60 and the pentacene molecules in the ''head-on'' orientation. It is noteworthy that the ultrafast electron transfer across this well-defined molecular heterojunction was demonstrated by time-resolved photoemission electron microscopy in a very recent work, 253 which suggests potential advantage of the heteroepitaxial molecular junctions for use of photovoltaic devices with efficient exciton dissociation.…”

Direct Observation of Photoexcited Electron Dynamics in Organic Solids Exhibiting Thermally Activated Delayed Fluorescence via Time‐Resolved Photoelectron Emission Microscopy

“…In this photoelectron yield spectrum, it is known that, below the onset energy of the photoelectron signal from the HOMO, the small “photoelectron onset from the LUMO” can be observed via a multiple excitation process within one pulse, which is quite useful for determining E A . [ 37 ] In Figure a, the photon energy dependence of the photoelectron yields of the 4CzIPN film is marked by blue dots. The laser pulse repetition rate was set to 10 kHz, and the photon energy was swept from ≈3.3 to 3.7 eV.…”

“…This results in photoelectron measurements with a large signal-to-noise (S/N) ratio even for insulating organic films, where photoelectron spectroscopy is usually quite difficult. [37][38][39] We previously showed that TR-PEEM could indeed be used to investigate the ultrafast dynamics of excitons, including their dissociation process at an organic heterointerface for photovoltaic applications. [37] However, there are no reports on the application of the TR-PEEM method to unveil the exciton dynamics during spin-flip events, i.e., TADF.…”

“…[37][38][39] We previously showed that TR-PEEM could indeed be used to investigate the ultrafast dynamics of excitons, including their dissociation process at an organic heterointerface for photovoltaic applications. [37] However, there are no reports on the application of the TR-PEEM method to unveil the exciton dynamics during spin-flip events, i.e., TADF. In this study, the dynamics of the photoexcited electrons during the TADF process were successfully and directly probed by TR-PEEM, providing precious and additional information compared with the results obtained from the conventional TR-PL and TAS methods.…”

Interface Structures and Electronic States of Epitaxial Tetraazanaphthacene on Single-Crystal Pentacene

“…A significant charge carrier mobility of 35 cm 2 V −1 s −1 at room temperature has been reported by space-charge-limited current measurements [ 1 ], and intermolecular electronic band dispersion was confirmed by angle-resolved photoelectron spectroscopy for the pentacene single crystals (PnSCs) [ 2 , 3 ]. In addition, pentacene is known to exhibit singlet exciton fission efficiently, which makes this molecule quite promising for application as an organic solar cell material [ 4 , 5 , 6 ].…”