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The recently developed narrow-band blue-emitting organoboron chromophores based on the multiple-resonance (MR) effect have now become one of the most important components for constructing efficient organic light emitting diodes (OLEDs). While they basically emit through fluorescence, they are also known for showing substantial thermally activated delayed fluorescence (TADF) even with a relatively large singlet–triplet gap (Δ E ST ). Indeed, understanding the reverse intersystem crossing (RISC) dynamics behind this peculiar TADF will allow judicious molecular designs toward achieving better performing OLEDs. Explaining the underlying nonadiabatic spin-flip mechanism, however, has often been equivocal, and how the sufficiently fast RISC takes place even with the sizable Δ E ST and vanishingly small spin–orbit coupling is not well understood. Here, we show that a vibronic resonance, namely the frequency matching condition between the vibration and the electronic energy gap, orchestrates three electronic states together and this effect plays a major role in enhancing RISC in a typical organoboron emitter. Interestingly, the mediating upper electronic state is quite high in energy to an extent that its thermal population is vanishingly small. Through semiclassical quantum dynamics simulations, we further show that the geometry dependent non-Condon coupling to the upper triplet state that oscillates with the frequency Δ E ST / ℏ is the main driving force behind the peculiar resonance enhancement. The existence of an array of vibrational modes with strong vibronic rate enhancements provides the ability to sustain efficient RISC over a range of Δ E ST in defiance of the energy gap law, which can render the MR-emitters peculiar in comparison with more conventional donor–acceptor type emitters. Our investigation may provide a new guide for future blue emitting molecule developments.

We report the effect of a nanobump assembly (NBA) constructed with molybdenum oxide (MoO3) covering Ag nanoparticles (NPs) under the active layer on the efficiency of plasmonic polymer solar cells. Here, the NPs with precisely controlled concentration and size have been generated by an atmospheric evaporation/condensation method and a differential mobility classification and then deposited on an indium tin oxide electrode via room temperature aerosol method. NBA structure is made by enclosing NPs with MoO3 layer via vacuum thermal evaporation to isolate the undulated active layer formed onto the underlying protruded NBA. Simulated scattering cross sections of the NBA structure reveal higher intensities with a strong forward scattering effect than those from the flat buffer cases. Experimental results of the device containing the NBA show 24% enhancement in short-circuit current density and 18% in power conversion efficiency compared to the device with the flat MoO3 without the NPs. The observed improvements are attributed to the enhanced light scattering and multireflection effects arising from the NBA structure combined with the undulated active layer in the visible and near-infrared regions. Moreover, we demonstrate that the NBA adopted devices show better performance with longer exciton lifetime and higher light absorption in comparison with the devices with Ag NPs incorporated flat poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Thus, the suggested approach provides a reliable and efficient light harvesting in a broad range of wavelength, which consequently enhances the performance of various organic solar cells.

The dynamic characterization of two green-sensitive organic photodetectors (OPDs) using nonfullerene small molecules is investigated by analyzing the electrical parameters based on the experimental results and the simulated data. The two OPDs comprise N,N-dimethyl quinacridone (DMQA) as the common donor and dibutyl-substituted dicyanovinyl terthiophene (DCV3T) or boron-subphthalocyanine chloride (SubPc) as respective acceptors. At the applied voltage of −5 V, the device composed of DMQA/SubPc shows a higher frequency response at 148.3 kHz, by 55 kHz higher than the device based on DMQA/DCV3T. The impedance spectroscopy results indicate that the former device exhibits the low resistance due to the high mobility and the low capacitance linked to the dielectric constant. According to the molecular quantum calculation, the linear structure of DCV3T may promote packing of adjacent molecules in the linear direction, resulting in a high polarizability. In contrast, the fused structure of SubPc leads to a decrease in reorganization energy, and its conical shape tends to counterbalance the net dipole at the axial position in the dimer packing configuration owing to the symmetry of the three-branched units in the molecular periphery, which are related to the high carrier mobility and the low dielectric constant. The OPD comprising SubPc, with the dynamic response surpassing the commercialization level of 100 kHz, also exhibits good static performance with an external quantum efficiency of 60.1% at the wavelength of 540 nm, which can be an interesting candidate for potential applications as image sensors.