High-Detectivity UV-Visible-NIR Broadband Polymer Photodetector with Polymer Charge Blocking Layer Cross-Linked by Organic Photocrosslinker

Abstract

Ultraviolet (UV), visible, and near-infrared (NIR) broadband organic photodetectors are fabricated by sequential solution-based thin film coatings of a polymer electron blocking layer (EBL) and a polymer photoactive layer. To avoid damage to a preceding polymer EBL during a subsequent solution-based film coating of a polymer photoactive layer due to lack of solvent orthogonality, 2-(((4-azido-2,3,5,6-tetrafluorobenzoyl)oxy)methyl)-2-ethylpropane-1,3-diyl bis(4-azido-2,3,5,6-tetrafluorobenzoate) (FPA-3F) is used as a novel organic cross-linking agent activated by UV irradiation with a wavelength of 254 nm. Solution-processed poly[N,N '-bis(4-butylphenyl)-N,N '-bis(phenyl)-benzidine] (poly-TPD) films, which are cross-linked with a FPA-3F photocrosslinker, are used for a preceding polymer EBL. A ternary blend film composed of PTB7-Th, COi8DFIC, and PC71BM is used as a NIR-sensitive organic photoactive layer with strong photosensitivity in multispectral (UV-visible-NIR) wavelengths of 300-1,050 nm. Poly-TPD films are successfully cross-linked even with a very small amount of 1 wt% FPA-3F. Small amounts of FPA-3F have little detrimental effect on the electrical and optoelectronic properties of the cross-linked poly-TPD EBL. Finally, organic NIR photodetectors with a poly-TPD EBL cross-linked by the small addition of FPA-3F (1 wt%) show the detectivity values higher than 1 x 1012 Jones for the entire UV-visible-NIR wavelengths from 300 nm to 1050 nm, and the maximum detectivity values of 1.41 x 1013 Jones and 8.90 x 1012 Jones at the NIR wavelengths of 900 and 1000 nm, respectively. An organic NIR photodetector is successfully fabricated using a cross-linked poly[N,N '-bis(4-butylphenyl)-N,N '-bis(phenyl)-benzidine] electron blocking layer (poly-TPD EBL) assisted by a novel organic photocrosslinker. The organic photodetector with crosslinked EBL shows a low dark current and shows detectivity values higher than 1 x 1012 Jones for the entire UV-visible-NIR wavelengths from 300 nm to 1050 nm. image