Fully Stretchable Optoelectronic Sensors Based on Colloidal Quantum Dots for Sensing Photoplethysmographic Signals

Abstract

Flexible and stretchable optoelectronic devices can be potentially applied in displays, biosensors, biomedicine, robotics, and energy generation. The use of nanomaterials with superior optical properties such as quantum dots (QDs) is important in the realization of wearable displays and biomedical devices, but specific structural design as well as selection of materials should preferentially accompany this technology to realize stretchable forms of these devices. Here, we report stretchable optoelectronic sensors manufactured using colloidal QDs and integrated with elastomeric substrates, whose optoelectronic properties are stable under various deformations. A graphene electrode is adopted to ensure extreme bendability of the devices. Ultrathin QD light-emitting diodes and QD photodetectors are transfer-printed onto a prestrained elastomeric layout to form wavy configurations with regular patterns. The layout is mechanically stretchable until the structure is converted to a flat configuration. The emissive and active area itself can be stretched or compressed by buckled structures, which are applicable to wearable electronic devices. We demonstrate that these stretchable optoelectronic sensors can be used for continuous monitoring of blood waves via photoplethysmography signal recording. These and related systems create important and unconventional opportunities for stretchable and foldable optoelectronic devices with health-monitoring capability and, thus, meet the demand for wearable and body-integrated electronics.

Stretchable and Washable Strain Sensor Based on Cracking Structure for Human Motion Monitoring

“…The buckling mechanism (e.g. wrinkled or wavy structure) 9,15,37,45 has been proven to be an effective strategy for fabricating stretchable devices from non-stretchable materials 36 , as the applied stress can be effectively absorbed by expansion of the buckled structure until fully straightened, and also the adhesion of the ink is improved 46 . Thus, the stretchability performance was dependent on the level of pre-strain 47 and electrically active areas of Ag-DS/CF were observed to remain intact during repeatable stretching up to strains of 75% in the direction of the X-axis for configuration 50.…”

Flexible quantum dot light-emitting diodes for next-generation displays

“…157 In 2017, Kim et al reported wearable photoplethysmographic (PPG) sensors that combined stretchable QLEDs and QD photodetectors. 158 The graphene-based transparent electrode provided extreme bendability for the QD-based LEDs and PDs. The QLED was transferred onto a prestrained elastomer to form a buckled structure, and displayed 70% stretchability.…”

Recent Advances in Flexible Inorganic Light Emitting Diodes: From Materials Design to Integrated Optoelectronic Platforms

“…In addition to the QD layers, transfer printing methods can apply to multilayer stacks that include the QD emitting layers, charge transport layers, conductive electrodes, and even substrate layers. [49c,53] By using a sacrificial fluoropolymer to provide low energy surfaces for release, this type of multilayer transfer printing process allows the incorporation of red‐ and green‐emitting QD assemblies with different, optimized electron transport layers (ZnO and TiO 2 ) and the same hole transport/anode layers. [49c] The independently tailored band alignments between green QDs/TiO 2 and red QDs/ZnO and well‐matched highest occupied molecular orbitals (HOMO)/lowest unoccupied molecular orbitals (LUMO) levels result in improved charge carrier injection efficiencies and accordingly higher EQEs.…”

“…[49c] The independently tailored band alignments between green QDs/TiO 2 and red QDs/ZnO and well‐matched highest occupied molecular orbitals (HOMO)/lowest unoccupied molecular orbitals (LUMO) levels result in improved charge carrier injection efficiencies and accordingly higher EQEs. Furthermore, the capability for transfer printing the entire QLED stack to prestrained elastomeric substrates yields fully stretchable, wavy QLED arrays through buckling processes . The bending radii in such systems can be as small as 35 µm without mechanical damage or electrical degradation.…”

“…These collective advances in flexible QLEDs follow from interdisciplinary research in synthetic chemistry, quantum physics, optoelectronic materials, and mechanical engineering, and yield interesting opportunities in emerging display technologies and skin‐mounted electronics. Representative examples for such applications[53,56b,c,59] appear in Section .…”