All-solution-processed ultraflexible wearable sensor enabled with universal trilayer structure for organic optoelectronic devices.

All-solution-processed organic optoelectronic devices can enable the large-scale manufacture of ultrathin wearable electronics with integrated diverse functions. However, the complex multilayer-stacking device structure of organic optoelectronics poses challenges for scalable production. Here, we establish all-solution processes to fabricate a wearable, self-powered photoplethysmogram (PPG) sensor. We achieve comparable performance and improved stability compared to complex reference devices with evaporated electrodes by using a trilayer device structure applicable to organic photovoltaics, photodetectors, and light-emitting diodes. The PPG sensor array based on all-solution-processed organic light-emitting diodes and photodetectors can be fabricated on a large-area ultrathin substrate to achieve long storage stability. We integrate it with a large-area, all-solution-processed organic solar module to realize a self-powered health monitoring system. We fabricate high-throughput wearable electronic devices with complex functions on large-area ultrathin substrates based on organic optoelectronics. Our findings can advance the high-throughput manufacture of ultrathin electronic devices integrating complex functions.

Waterproof and ultraflexible organic photovoltaics with improved interface adhesion.

Ultraflexible organic photovoltaics have emerged as a potential power source for wearable electronics owing to their stretchability and lightweight nature. However, waterproofing ultraflexible organic photovoltaics without compromising mechanical flexibility and conformability remains challenging. Here, we demonstrate waterproof and ultraflexible organic photovoltaics through the in-situ growth of a hole-transporting layer to strengthen interface adhesion between the active layer and anode. Specifically, a silver electrode is deposited directly on top of the active layers, followed by thermal annealing treatment. Compared with conventional sequentially-deposited hole-transporting layers, the in-situ grown hole-transporting layer exhibits higher thermodynamic adhesion between the active layers, resulting in better waterproofness. The fabricated 3 µm-thick organic photovoltaics retain 89% and 96% of their pristine performance after immersion in water for 4 h and 300 stretching/releasing cycles at 30% strain under water, respectively. Moreover, the ultraflexible devices withstand a machine-washing test with such a thin encapsulation layer, which has never been reported. Finally, we demonstrate the universality of the strategy for achieving waterproof solar cells.

Surface-Energy-Mediated Interfacial Adhesion for Mechanically Robust Ultraflexible Organic Photovoltaics.

Insufficient interfacial adhesion is a widespread problem across multilayered devices that undermines their reliability. In flexible organic photovoltaics (OPVs), poor interfacial adhesion can accelerate degradation and failure under mechanical deformations due to the intrinsic brittleness and mismatching mechanical properties between functional layers. We introduce an argon plasma treatment for OPV devices, which yields 58% strengthening in interfacial adhesion between an active layer and a MoOX hole transport layer, thus contributing to mechanical reliability. The improved adhesion is attributed to the increased surface energy of the active layer that occurred after the mild argon plasma treatment. The mechanically stabilized interface retards the flexible device degradation induced by mechanical stress and maintains a power conversion efficiency of 94.8% after 10,000 cycles of bending with a radius of 2.5 mm. In addition, a fabricated 3 µm thick ultraflexible OPV device shows excellent mechanical robustness, retaining 91.0% of the initial efficiency after 1000 compressing-stretching cycles with a 40% compression ratio. The developed ultraflexible OPV devices can operate stably at the maximum power point under continuous 1 sun illumination for 500 min with an 89.3% efficiency retention. Overall, we validate a simple interfacial linking strategy for efficient and mechanically robust flexible and ultraflexible OPVs.

Simple Method for Creating Hydrophobic Ultraflexible Photovoltaics.

Optoelectronic devices, such as photodetectors and photovoltaics, are susceptible to surface contamination or water damage that can lead to reductions in performance or stability. Applying superhydrophobic coatings to these devices can introduce self-cleaning behavior and water resistance to extend their lifetime and improve their efficiency. However, existing methods for inducing superhydrophobicity have not been compatible with ultraflexible devices because of their thickness and complexity requirements. In this work, we introduce a procedure for inducing superhydrophobic and self-cleaning behavior on ultraflexible components using a combination of shrinkage-induced wrinkles and a low-surface-energy coating. We apply these techniques to an ultraflexible organic photovoltaics and demonstrate excellent hydrophobicity and self-cleaning behavior.

Smart Face Mask Based on an Ultrathin Pressure Sensor for Wireless Monitoring of Breath Conditions.

A smart face mask that can conveniently monitor breath information is beneficial for maintaining personal health and preventing the spread of diseases. However, some challenges still need to be addressed before such devices can be of practical use. One key challenge is to develop a pressure sensor that is easily triggered by low pressure and has excellent stability as well as electrical and mechanical properties. In this study, a wireless smart face mask is designed by integrating an ultrathin self-powered pressure sensor and a compact readout circuit with a normal face mask. The pressure sensor is the thinnest (totally compressed thickness of ≈5.5 µm) and lightest (total weight of ≈4.5 mg) electrostatic pressure sensor capable of achieving a peak open-circuit voltage of up to ≈10 V when stimulated by airflow, which endows the sensor with the advantage of readout circuit miniaturization and makes the breath-monitoring system portable and wearable. To demonstrate the capabilities of the smart face mask, it is used to wirelessly measure and analyze the various breath conditions of multiple testers.

Direct gold bonding for flexible integrated electronics.

Flexible and stable interconnections are critical for the next generation of shape-conformable and wearable electronics. These interconnections should have metal-like conductivity and sufficiently low stiffness that does not compromise the flexibility of the device; moreover, they must be achieved using low-temperature processes to prevent device damage. However, conventional interconnection bonding methods require additional adhesive layers, making it challenging to achieve these characteristics simultaneously. Here, we develop and characterize water vapor plasma­assisted bonding (WVPAB) that enables direct bonding of gold electrodes deposited on ultrathin polymer films. WVPAB bonds rough gold electrodes at room temperature and atmospheric pressure in ambient air. Hydroxyl groups generated by the plasma assist bonding between two gold surfaces, allowing the formation of a strong and stable interface. The applicability of WVPAB-mediated connections to ultrathin electronic systems was also demonstrated, and ultraflexible organic photovoltaics and light-emitting diodes fabricated on separate films were successfully interconnected via ultrathin wiring films.