Effect of Organic Molecular Volume on Organic Photodiodes

The development of light-absorbing organic molecules with calculated oscillator strength (f) is widely investigated to improve the performances of organic photoelectric devices such as organic photodiodes (OPDs). The oscillator strength estimates the probability of radiative electronic transition of a single molecule. However, most photoelectric devices are composed of organic thin films rather than a single organic molecule. Herein, the molecular volume is considered the critical parameter for the design of organic molecules. Three novel organic molecules, Et-H, Me-Me, and Me-H, with similar oscillator strengths and different molecular volumes, are designed and synthesized as proof-of-concept. Their experimental absorption properties and organic photodiode performances are investigated. Me-H, which has the smallest molecular volume and highest molecular packing density, shows the highest absorption coefficient in organic thin films and the best OPD performance with the highest external quantum efficiency.