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, P_Zn-FL, via Sonogashira coupling between an ethyne π-linked porphyrin core (P_Zn) and four fluorene (FL) moieties. The synthesized P_Zn-FL material showed a narrow full-width-at-half-maximum (FWHM) of 75 nm in the blue absorption region. The Q-band absorption of P_Zn-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 × 10⁻¹² W/Hz^0.5. The planar backbone structure of P_Zn-FL was beneficial to increase charge transport and reduce bimolecular recombination, and the vertically oriented alkyl side chains of the P_Zn backbone contributed to prevent severe intermolecular aggregation and maintain a narrow absorption in film state.