Dynamic Characterization of Green-Sensitive Organic Photodetectors Using Nonfullerene Small Molecules: Frequency Response Based on the Molecular Structure

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.