Narrow Band Organic Photodiode with Photoresponse at 808 nm for Photoplethysmography

The fabrication and characterization of an all polymers-based bulk heterojunction type organic photodiode having a narrowband response in the near-infrared spectral region with full width at half-maxima of 63 nm is reported. The active layer of the photodiode constitutes a 1:1 (by weight) blend of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] (PCE10) and poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diy1]-alt-5,5′-(2,2′-dithiophene)} (N2200) deposited using solution processing. The device exhibits a linear dynamic range of 35 dB, response speed of 893 kHz, and specific-detectivity of 10⁹ Jones at 808 nm excitation wavelength. The narrowband response is achieved using the charge collection narrowing mechanism in a 2.7 μm thick junction device.