Design and Fabrication of High-Performance Organic Photodetector for Ambient Light PPG Sensor

Organic photodetectors (OPDs) developed using novel semiconductor materials and well-designed device architectures have been rapidly progressing in recent years. In this article, we report the design, fabrication, and characterization of a high-performance OPD for detecting green light. The OPD is based on [Poly (3-hexylthiophene-2, 5-diyl)] (P3HT): PC61BM ( [6] , [6] -phenyl-C61-butyric acid methyl ester) active layer and an innovative hole transport layer (HTL) made from combination of polyethylenimine (PEI) interlayer and Copper (I) thiocyanate (CuSCN) interface layer. The innovative HTL significantly reduces the dark current and improves other optoelectronic properties of OPDs, including linear dynamic range (LDR) and specific detectivity. Results show that the newly designed OPDs have an extremely low dark current ( $\sim $ 100 pA), high detectivity ( $\sim $ 1013 Jones), and a large LDR of 180 dB. Compared to the conventional OPDs the newly designed OPDs show the capability to detect light at intensities two order of magnitude lower values. Application of the OPDs for photoplethysmography (PPG) sensing demonstrates that the newly designed photodetectors can successfully acquire PPG signal under ambient light condition without turning on any light-emitting diode (LED) and can have potential for development of low power PPG sensing wearables.