Stretchable Photodiodes with Polymer-Engineered Semiconductor Nanowires for Wearable Photoplethysmography

Abstract

Healthcare systems worldwide have been stressed to provide sufficient resources to serve the increasing and aging population in our society. The situation became more challenging at the time of pandemic. Technology advancement, especially the adoption of wearable health monitoring devices, has provided an important supplement to current clinical equipment. Most health monitoring devices are rigid, however, human tissues are soft. Such a difference has prohibited intimate contact between the two and jeopardized wearing comfortableness, which hurdles measurement accuracy especially during longtime usage. Here, we report a soft and stretchable photodiode that can conformally adhere onto the human body without any pressure and measure cardiovascular variables for an extended period with higher reliability than commercial devices. The photodiode used a composite light absorber consisting of an organic bulk heterojunction embedded into an elastic polymer matrix. It is discovered that the elastic polymer matrix not only improves the morphology of the bulk heterojunction for obtaining the desired mechanical properties but also alters its electronic band structure and improves the electrical properties that lead to a reduced dark current and enhanced photovoltage in the stretchable photodiode. The work has demonstrated high fidelity measurements and longtime monitoring of heat rate variability and oxygen saturation, potentially enabling next-generation wearable photoplethysmography devices for point-of-care diagnosis of cardiovascular diseases in a more accessible and affordable way.

Organic Electronics in Biosensing: A Promising Frontier for Medical and Environmental Applications

“…Seesaard and Wongchoosuk [231] introduced a fabric-based piezoresistive force sensor array composed of a Ti 3 AlC 2 /PEDOT:PSS nanocomposite with ultrahigh sensitivity (up to 1.51 N −1 ) that is suitable for wearable e-textile applications. In another study, Mao et al [232] developed a soft, stretchable photodiode with a composite light absorber and an organic bulk heterojunction within an elastic polymer matrix for reliable cardiovascular variable measurements. The developed photodiode effectively monitors variables such as heart rate variability and oxygen saturation over extended periods.…”

Forming Long-Range Order of Semiconducting Polymers through Liquid-Phase Directional Molecular Assemblies

“…Semiconducting polymers have garnered significant attention in the field of organic electronics due to their attractive combination of electronic properties, mechanical flexibility/stretchability, and solution-processability for a broad range of device applications. − However, the random interactions among solvents, solutes, and substrates during solution-processing often disrupt molecular stacking, leading to disorder or local order with misaligned molecular orientations. This misalignment compromises the accuracy of device characterizations and calls for the establishment of long-range order with a cohesive molecular orientation.…”