Hyeonghun Kim

Filter-free discrimination of visible (VIS) and near-infrared (NIR) light within a single photodetector pixel remains challenging because conventional photodiodes typically require optical filters or multiple detector elements. This work reports a monolithic nonlinear back-to-back photodiode (NL-BPD) that enables bias-programmable reconfiguration between high-linear-dynamic-range (LDR) photodetection and nonlinear spectral-discrimination modes. By changing the bias from − 0.5 V to + 0.5 V, the device's initially independent linear responses in both VIS and NIR channels (LDRs ≥ 100 dB) evolve into a nonlinear regime in which the VIS response reverses polarity with increasing light intensity while the NIR response remains monotonic. This behavior is enabled by defect-assisted transport pathways formed through partial interfacial reactions between the highly conductive PEDOT:PSS interlayer and MAPbI ₃ . Together with the optimized device architecture, this interfacial current-path engineering reduces resistive bottlenecks and promotes cooperative carrier extraction from both absorbers. The resulting electrical signatures allow mixed VIS–NIR signals to be decoded from a single electrical output without optical filters or spatially separated pixels. The NL-BPD enables accurate spectral reconstruction (average R ² = 0.9996), demonstrates single-point pulse oximetry, and achieves > 96% accuracy in normalized-difference-vegetation-index-based vegetation health classification. These results establish bias-programmable nonlinear photodetection as an effective strategy for single-pixel multispectral sensing.

Humidity sensing is important for environmental monitoring and biomedical diagnostics, with electrical and optical transduction being among the most widely used approaches. However, electrical sensors typically require external bias for signal readout, whereas optical sensors often face challenges in quantitative and device-integrated signal acquisition. Here, we report a PEDOT:PSS-MXene hybrid thin film integrated on n-Si that simultaneously provides humidity-induced reflectance modulation and light-driven zero-bias photocurrent generation. Humidity-induced swelling of the hybrid layer modulates visible-band thin-film interference on the Si platform, producing reflectance and color changes. In parallel, the n-Si/PEDOT:PSS-MXene heterojunction generates a built-in electric field that converts humidity-modulated optical absorption into photocurrent under illumination without external bias. The dual responses originate from the same active layer but proceed through distinct optical and electronic channels. Rigorous coupled-wave analysis using literature-tabulated complex refractive indices of Si and PEDOT:PSS reproduces the experimentally observed CIE 1931 chromaticity trajectory over 0–90% relative humidity. Under 470 nm illumination, the optimized 50:50 (v/v) hybrid device exhibits a response of 331.9% at 100% RH, corresponding to a 3.4-fold enhancement over pristine PEDOT:PSS. The device further resolves human respiration up to 24 breaths min-1, covering and exceeding the typical resting physiological range of 12–20 breaths min-1. The proposed Si-compatible, single-layer dual-readout architecture offers a route toward self-powered wearable respiratory sensors based on integrated optoelectronic humidity sensing.

All‐inorganic halide perovskites, such as Cs ₄ PbBr ₆ /CsPbBr ₃ , exhibit excellent optical properties and intrinsic stability as 0D materials, rendering them attractive for photonic applications. However, the vulnerability of these materials to moisture and heat necessitates the implementation of stabilization strategies. Conventional solution‐based methods, such as doping or surface passivation, often require solvents that reduce uniformity and degrade optical performance. To overcome these limitations, a solvent‐free powder atomic layer deposition (PALD) technique to coat Cs ₄ PbBr ₆ /CsPbBr ₃ powders with conformal Al ₂ O ₃ nanolayers is employed. The PALD‐grown layer effectively passivated surface defects, suppressed Br vacancies, and stabilized the crystal structure of the perovskite in steam and polar solvents and under heat exposure. Importantly, relative photoluminescence quantum yield increased by up to 14% compared to the uncoated powders. Based on these strategies, it is fabricated a UV‐responsive photoluminescent film by integrating Al ₂ O ₃ ‐coated Cs ₄ PbBr ₆ /CsPbBr ₃ (green emission under UVA/UVB) with Al ₂ O ₃ ‐coated Cs ₂ Cu ₃ I ₅ (blue emission under UVB/UVC), achieving clear wavelength‐discriminable emissions, i.e., green, sky blue, and deep blue under UVA, UVB, and UVC illumination, respectively. This study demonstrates the potential of PALD as a scalable, solvent‐free passivation method that enhances the environmental stability and optical performance of halide perovskites, thereby improving their commercial viability for use in next‐generation optoelectronic devices.

This review delves into the advancements in optoelectronic logic gate (OELG) devices, emphasizing their transformative potential in computational technology through the integration of optical and electronic components. OELGs present significant advantages over traditional electronic logic gates, including enhanced processing speed, bandwidth, and energy efficiency. The evolution of OELG architectures from single‐device, single‐logic systems to more sophisticated multidevice, multilogic, and reconfigurable OELGs is comprehensively explored. Key advancements include the development of materials and device structures enabling multifunctional logic operations and the incorporation of in‐memory functionalities, critical for applications in high‐performance computing and real‐time data processing. This review also addresses the challenges that need to be overcome, such as stability, durability, integration with existing semiconductor technologies, and efficiency. By summarizing current research and proposing future directions, this review aims to guide the ongoing development of next‐generation optoelectronic architectures, poised to redefine the landscape of optical computing, communication, and data processing.

Selective spectral discrimination of visible and near‐infrared light, which accurately distinguishes different light wavelengths, holds considerable promise in various fields, such as automobiles, defense, and environmental monitoring. However, conventional imaging technologies suffer from various issues, including insufficient spatial optimization, low definition, and optical loss. Herein, a groundbreaking advancement is demonstrated in the form of a dual‐band photodiode with distinct near‐infrared‐ and visible‐light discrimination obtained via simple voltage control. The approach involves the monolithic stacking integration of methylammonium lead iodide (MAPbI₃) and Si semiconductors, resulting in a p‐Si/n‐phenyl‐C₆₁‐butyric acid methyl ester/i‐MAPbI₃/p‐spiro‐MeOTAD (PNIP) device. Remarkably, the PNIP configuration can independently detect the visible and near‐infrared regions without traditional optical filters under a voltage range of 3 to −3 V. In addition, an imaging system for a prototype autonomous vehicle confirms the capability of the device to separate visible and near‐infrared light via an electrical bias and practicality of this mechanism. Therefore, this study pushes the boundaries of image sensor development and sets the stage for fabricating compact and power‐efficient photonic devices with superior performance and diverse functionality.

The explosive demand for a wide range of data processing has sparked interest towards a new logic gate platform as the existing electronic logic gates face limitations in accurate and fast computing. Accordingly, optoelectronic logic gates (OELGs) using photodiodes are of significant interest due to their broad bandwidth and fast data transmission, but complex configuration, power consumption, and low reliability issues are still inherent in these systems. Herein, we present a novel all-in-one OELG based on the bipolar spectral photoresponse characteristics of a self-powered perovskite photodetector (SPPD) having a back-to-back p⁺-i-n-p-p⁺ diode structure. Five representative logic gates (“AND”, “OR”, “NAND”, “NOR”, and “NOT”) are demonstrated with only a single SPPD via the photocurrent polarity control. For practical applications, we propose a universal OELG platform of integrated 8 × 8 SPPD pixels, demonstrating the 100% accuracy in five logic gate operations irrelevant to current variation between pixels.

With the dramatic progress of Internet-of-Things technology and Artificial Intelligence (AI) algorithms, portable healthcare monitoring has been highlighted as a facile pre-diagnosing strategy for tracking individual health status without hospitalization. In this regard, a wide range of wearable sensors, which extract bio-information such as body temperature, blood pressure, or respiratory patterns, have been developed so far. Although numerous factors are considered during sensor development depending on the types of analytes or target locations in the human body, acquiring sufficient flexibility must be a priority to endure uncontrollable stress caused by the surrounding conditions. Diverse flexible materials have been exploited as suitable substrates for wearable sensors that fulfill the desired mechanical stability. Among them, textiles have tremendous advantages in terms of remarkable stability, skin compatibility, lightweight, and breathability. However, owing to their inherently rough surface, high porosity, and surface hydrophobicity, the formation of a uniform sensing film on fabric has been regarded as a much daunting task compared to a flat and rigid substrate. Liquid-phase coating methods such as spin-coating, dip-casting, or doctor-blading have failed to create a uniform and reproducible film on a fabric. Additives like binders are sometimes effective for improving conformability, but creating thin layers, which is significant for high-performance sensors, still remains challenging. Vapor phase coating methods are, arguably, the most efficient tactics for coating sensing films on fabrics. Inorganic or metallic materials, deposited by a comprehensive deposition tool based on physical vapor deposition, chemical vapor deposition, or atomic layer deposition techniques, have been typically considered as active materials for strain sensors, thermometers, or pressure sensors. However, the inorganic materials with poor flexibility or stretchability are vulnerable to be cracked readily even under mild mechanical stress. Thus, exploring materials and contriving their proper coating methods should be further progressed for realizing desired fabric-based wearable sensors. Herein, we utilize the oxidative chemical vapor deposition (oCVD) technique for creating a conformal Poly(3,4-ethylene dioxythiophene) (PEDOT) layer on multiple fabrics (nylon, polyester, and cotton) without any binder or additives. The oCVD is capable of creating a highly conductive PEDOT (nominally, 1-10 S cm^-1 on cotton fabric; 500-1500 S cm^-1 on glasses) of which thickness is readily controllable from 50 nm to 1 μm by varying the deposition time. Moreover, the mechanical stability, breathability, and lightness of fabrics are consistent even after PEDOT coating, implying the oCVD could form a promising sensing material while maintaining all advantages of fabrics. Based on the unique properties of excellent conformality, high conductivity, and good mechanical flexibility^1-5, we fabricate simple resistive-typed sensors by directly printing the PEDOT on a commercial glove and disposable mask, consisting of polymers such as polypropylene or polyester. The glove and mask sensors are capable of extracting blood pressure information and respiratory rates in real-time with remarkable precision. This is the first report proving the usability of the oCVD method on fabric-based sensors, thus, paving the way for developing versatile healthcare devices. This work was partly supported by the NSF Award No. ECCS-1931088. References Lee, S.; Song, H. W.; Cho, J. Y.; Radevski, N.; Truc, L. N. T.; Sung, T. H.; Jiang, Z. T.; No, K., Mobility of Air-Stable p-type Polythiophene Field-Effect Transistors Fabricated Using Oxidative Chemical Vapor Deposition. Journal of Electronic Materials 2020, 49 (6), 3465-3471. Drewelow, G.; Wook Song, H.; Jiang, Z.-T.; Lee, S., Factors controlling conductivity of PEDOT deposited using oxidative chemical vapor deposition. Applied Surface Science 2020, 501, 144105. Lee, S.; Borrelli, D. C.; Jo, W. J.; Reed, A. S.; Gleason, K. K., Nanostructured Unsubstituted Polythiophene Films Deposited Using Oxidative Chemical Vapor Deposition: Hopping Conduction and Thermal Stability. Advanced Materials Interfaces 2018, 5 (9). Lee, S.; Gleason, K. K., Enhanced Optical Property with Tunable Band Gap of Cross-linked PEDOT Copolymers via Oxidative Chemical Vapor Deposition. Adv. Funct. Mater. 2015, 25 (1), 85-93. Lee, S.; Paine, D. C.; Gleason, K. K., Heavily Doped poly(3,4-ethylenedioxythiophene) Thin Films with High Carrier Mobility Deposited Using Oxidative CVD: Conductivity Stability and Carrier Transport. Adv. Funct. Mater. 2014, 24 (45), 7187-7196. Figure 1

Health-monitoring sensors directly fabricated on disposable wears using oxidative chemical vapor deposition.