High Detectivity Near-Infrared Organic Photodetectors with the Cross-Linked Electron Blocking Layer Using a Novel Photoinitiator

Near-infrared (NIR) organic photodetectors with high detectivity are fabricated with an organic electron blocking layer (EBL) with an appropriate energy band alignment. To avoid damage to a preceding organic electron blocking layer during a subsequent coating of an organic photoactive layer, cross-linking technology using a novel photoinitiator is used for an EBL. Poly-TPD is used as an EBL due to its appropriate energy band alignment with a NIR organic sensitizing layer. A ternary blend film composed of PTB7-Th, CO_i8DFIC, and PC₇₁BM are used as a NIR sensitizing layer with strong photosensitivity in multi-spectral (UV-Visible-NIR) wavelengths of 300-1,000 nm. By measuring the optical properties of poly-TPD films, first of all, it clearly shows that cross-linked poly-TPD EBL is not washed by organic solvents used for coating a NIR sensitizing layer. The organic NIR photodetector with an EBL mixing a photoinitiator of 1 wt% shows the highest detectivity of 1.16 × 10¹³ Jones at 900 nm due to significantly low dark current (1.5 × 10^-6 mA cm-2 at -0.1 V). In this work, the effect of a photoinitiator is systematically studied using the various amounts of photoinitiator.