(Invited) Precise Determination of Exciton Binding Energy of Organic Semiconductors

Strongly bound excitons in organic semiconductors are crucial for the operation of organic optoelectronic devices. However, accurate experimental data on the exciton binding energy of organic semiconductors are lacking. In this study, we determine the exciton binding energy as the difference between the optical and transport bandgaps with a precision of 0.1 eV. From the systematic study of the exciton binding energy of 42 organic semiconductors (15 non-fullerene acceptors, 4 fullerene acceptors, 13 low-bandgap polymers, 7 organic light-emitting diode materials, and 3 crystalline materials), we found that the exciton binding energy is a quarter of the transport gap regardless of the material. We interpret this unexpected relationship in terms of a hydrogen atom model.