Future electronics will need to be mechanically flexible and stretchable in order to enable the development of lightweight and conformal applications. In contrast, photodetectors, an integral component of electronic devices, remain rigid, which prevents their integration into everyday life applications. In recent years, significant efforts have been made to overcome the limitations of conventional rigid photodetectors, particularly their low mechanical deformability. One of the most promising routes toward facilitating the fabrication of flexible photodetectors is to replace conventional optoelectronic materials with nanomaterials or organic materials that are intrinsically flexible. Compared with other functional materials, organic polymers and molecules have attracted more attention for photodetection applications due to their excellent photodetection performance, cost-effective solution-fabrication capability, flexible design, and adaptable manufacturing processes. This article comprehensively discusses recent advances in flexible organic photodetectors in terms of optoelectronic, mechanical properties, and hybridization with other material classes. Furthermore, flexible organic photodetector applications in health-monitoring sensors, X-ray detection, and imager devices have been surveyed.

This research contributes to work on synthesizing zinc oxide nanoparticles (ZnO NPs) at room temperature (RT) and their utilization in flexible gas sensors. RT ZnO NP synthesis with a basicity solution (pH ≈ 13) demonstrates an efficient method for synthesizing well-crystalline ZnO NPs (RT.pH13) comparable to those synthesized by the hydrothermal method (hyd.C). The RT.pH13 achieved a high thermal stability with minimal organic reside impurities (~4.2 wt%), 30–80 nm particle size distribution, and a specific surface area (14 m² g⁻¹). The synthesized pre- and post-calcinated RT.pH13 NPs were then incorporated into flexible sensors for gas sensing applications at ambient conditions (RT and relative humidity of 30–50%). The pre-calcinated ZnO-based sensor (RT.pH13) demonstrated superior sensitivity to styrene and acetic acid and lower sensitivity to dimethyl-6-octenal. The calcinated ZnO-based sensor (RT.pH13.C) exhibited lower sensitivity to styrene and acetic acid, but heightened sensitivity to benzene, acetone, and ethanol. This suggests a correlation between sensitivity and structural transformations following calcination. The investigation of the sensing mechanisms highlighted the role of surface properties in the sensors’ affinity for specific gas molecules and temperature and humidity variations. The study further explored the sensors’ mechanical flexibility, which is crucial for flexible Internet of Things (IoT) applications.

This study explores optimizing interlayers in flexible, self‐powered organic photodetectors (OPDs). Integration of conductive PEDOT:PSS (poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate)), PH1000 flexible anodes on PET substrates demonstrates that PH1000 outperforms traditional ITO (Indium tin oxide) anodes, offering higher optical transmittance, minimal surface roughness, and superior mechanical stability, with less than 10% resistance change after 2000 bending cycles. Various hole transport layers (HTLs) and electron transport layers (ETLs) are studied, showing that their incorporation reduces dark current and increases photocurrent at zero bias. Mott‐Schottky analysis reveals that HTLs and ETLs improve exciton dissociation. CuSCN (Copper(I) thiocyanate) HTL and PFN‐Br (Poly(9,9‐bis(3′‐(N,N‐dimethyl)‐N‐ethylammoinium‐propyl‐2,7‐fluorene)‐alt‐2,7 (9,9‐dioctylfluorene))dibromide) ETL provide the highest performance enhancements, reducing trap density and improving exciton dissociation. Capacitance‐frequency measurements and photoluminescence spectroscopy confirm enhanced exciton dissociation due to reduced binding energy, especially for CuSCN. Charge collection efficiency (CCE) is significantly improved, with CuSCN ETL and PFN‐Br ETL achieving a CCE of over 22.93% at zero bias. PH1000‐based, zero‐biased OPDs with CuSCN and PFN‐Br show a maximum responsivity of 0.23 A/W, specific detectivity of 3.89 × 10 ^{1 2} Jones, rapid response times, and excellent mechanical stability. These OPDs, integrated into an ambient light‐based photoplethysmography sensing system, provide accurate heart rate monitoring, demonstrating their potential for next‐generation low power wearables.

Advances in biomaterials and carbon nanostructures are enabling next-generation relative humidity (RH) sensors with broad applications. Here we report a gelatin-modified graphene ink (Ge-GTr), an eco-friendly formulation that delivers high-performance RH sensing when printed by aerosol jet. Devices fabricated with optimized 1.0Ge-GTr ink exhibited reliable operation across 10–90% RH at room temperature, with two distinct response regimes: 0.58% RH⁻¹ sensitivity at ≤ 60% RH (charge transfer/dielectric screening) and 2.5% RH⁻¹ at ≥ 60% RH (gelatin micelle swelling). The sensors achieved a peak response of 102% at 90% RH, resolution of ±2% RH, response time of ~75 s, and only 3% hysteresis between 30–70% RH. They also showed repeatable cycling behavior, robust temperature stability, and excellent mechanical flexibility. Demonstrations in breath analysis and food packaging confirmed their practical utility: the sensors distinguished breathing patterns of smokers and non-smokers and detected spoilage-related RH in meat packages, while maintaining high selectivity to RH over interfering gases. These results highlight Ge-GTr as a sustainable route to flexible, printed RH sensors for health monitoring and smart packaging applications.

In this research, we introduce an innovative wearable device capable of capturing photoplethysmography (PPG) signals under two conditions: No-LED and low-intensity LED. Incorporation of both modes substantially reduces power consumption by recording the PPG signal without active light emission when there is sufficient ambient light, thereby enhancing the device’s overall energy efficiency and extending its battery life. The wearable device consists of two main parts: the ring (sensor) and the bracelet (read-out unit) which are connected by a flexible connector. The design of the ring and the placement of the LEDs and photodiodes in the ring have been optimized to ensure consistent PPG signal acquisition across diverse user profiles. An accelerometer is integrated in the ring to mitigate motion artifacts from PPG signal. The bracelet part receives PPG and accelerometer data from the ring and transmits them wirelessly to a remote device for further processing and display. Our experimental results indicate that the proposed system achieves a maximum measurement error of 3 bpm for heart rate and 2.9% for oxygen saturation compared to the reference measurements, demonstrating the wearable’s capability to capture PPG signals in both modes. The readout of our wearable device consumes 262.5 μW continuously in no LED mode and 652.5μW in low-intensity LED mode, indicating the No-LED mode can significantly extend the battery life. The proposed wearable engineered to acquire two different wavelengths PPG signals in low-intensity LED and No-LED modes has potential for accurate monitoring of vital physiological parameters while reducing power consumption.

Efficient synthesis routes for zinc oxide nanoparticles (ZnO NPs) that are rapid and non-toxic and operate at room temperature (RT) are essential to expand accessibility, minimize environmental impact, and enable integration with temperature-sensitive substrates. In this work, ZnO NPs were synthesized by probe ultrasonication at RT for durations from 30 s to 10 min and benchmarked against our previously reported water bath sonication method. A 10-min probe treatment yielded highly uniform ZnO NPs with particle sizes of 60–550 nm and a specific surface area of up to 75 m² g⁻¹, compared to ~38 m² g⁻¹ for bath sonication. These features were largely preserved after calcination at 500 °C. When integrated into chemiresistive devices, the resulting ZnO (P(10))-based sensors exhibited pronounced selectivity toward styrene, showing reversible responses at low concentrations (10–50 ppm) and stronger signals at higher levels (up to 200 ppm, with resistance changes reaching 2930%). The sensors demonstrated stable operation across 10–90% relative humidity, and consistent performance from −20 °C to 180 °C. Flexibility tests confirmed reliable sensing after 100 bending cycles at 30°. Overall, RT-probe ultrasonication offers a rapid, scalable, and eco-friendly route to ZnO NPs with tunable properties, opening new opportunities for flexible gas sensing.