Wavelength-selective porphyrin photodiodes via control of Soret- and Q-band absorption

Porphyrin-based photodiode materials have mainly been targeted to achieve panchromatic absorption by maximizing the Soret- and Q-band absorption; however, they have rarely been studied with the purpose to make them wavelength-selective in photodetecting devices. In this study, we synthesized a wavelength-selective porphyrin material, PZn-FL, via Sonogashira coupling between an ethyne pi-linked porphyrin core (PZn) and four fluorene (FL) moieties. The synthesized PZn-FL material showed a narrow full-width-at-half-maximum (FWHM) of 75 nm in the blue absorption region. The Q-band absorption of PZn-FL was significantly suppressed in organic photodiodes (OPDs), resulting in a blue-selective specific detectivity spectrum with a FWHM of 75 nm and a noise equivalent power of 2.86 x 10-12 W/Hz0.5. The planar backbone structure of PZn-FL was beneficial to increase charge transport and reduce bimolecular recombination, and the vertically oriented alkyl side chains of the PZn backbone contributed to prevent severe intermolecular aggregation and maintain a narrow absorption in film state.