Jianguo Mei

Haze is a key parameter that characterizes the optical clarity of transmissive materials. In real‐world applications of organic electrochromic devices, however, the origin of haze formation and its connection to film morphology remain poorly understood, despite its significant impact on user safety and visual comfort. This study elucidates the origin of haze formation in electrochromic polymer (ECP) films by analyzing the morphology of a propylenedioxythiophene (ProDOT)‐based ECP‐black, a broadband, neutral density, absorbing ECP that is one of the most important in electrochromic field. ECP solutions were prepared with a controlled amount of antisolvent, followed by thermal annealing to tune the polymer morphology. Based on Mie scattering theory, surface roughness and polymer aggregate size are identified as the primary factors responsible for haze formation. In addition, haze is shown to vary with film thickness and aggregation‐induced microvoids. This work provides fundamental insight into haze formation in organic electrochromic films and establishes strategies for controlling haze that can impair device performance.

Transparent capacitive ion storage layers are essential for electrochromic devices (ECDs) because they determine charge balance, electrochemical switching kinetics, optical neutrality, and bistability. However, their electrochemical structural dynamics and their relationship with ECD performance remain insufficiently understood compared with that of the active electrochromic material itself. Here, we investigate nanoengineered indium tin oxide (ITO) nanoparticles and PEDOT:PSS as transparent capacitive ion storage layers for p-type polymer-based ECDs. ITO nanoparticles show robust, optically neutral double-layer capacitance for fast ECD responses with high coloration efficiency, whereas PEDOT:PSS exhibits pseudocapacitive mixed ionic/electronic transport with pronounced optical memory. By combining electrochemical analysis on morphological and crystalline dynamics, we reveal that ITO nanoparticles maintain stable morphology and crystallinity, while PEDOT:PSS undergoes electrochemically induced lamellar densification without surface degradation during electrochemical operation. PEDOT:PSS is further utilized as a capacitive transparent working electrode after polar-solvent vapor annealing, which provides high electrical conductivity and a mixed-conducting capacitive interface adjacent to the electrochromic polymers. When combined with interfacial charge-buffering PEDOT:PSS electrodes and optically passive nanoengineered ITO, the polymeric ECDs exhibit large optical density change, fast coloration and bleaching responses, and high optical memory.

Retinomorphic hardware, inspired by the human visual system, integrates sensing and preprocessing within the same device and requires optoelectronic pixels capable of electrically encoding photoresponse into antagonistic ON and OFF pathways. Existing approaches generally rely on gated architecture or high-voltage polarization switching (typically >1 V), which increases circuit complexity and dynamic power consumption for device reconfiguration. Here, we report a vertical two-terminal organic optoelectronic design based on a single-layered-doped conducting polymer, n-doped poly(benzodifurandione) (n-PBDF), with asymmetric electrodes. Leveraging electrode asymmetric work function and polymer doping engineering, the proposed device achieves continuous analog tuning of photoresponse polarity from negative to positive at low operational voltage (<0.2 V), enabling the emulation of antagonistic visual encoding. The n-PBDF-based device also exhibits robust reversible negative-to-positive photoresponse switching for 106 cycles and stable retention for 78 days under ambient conditions. These characteristics, together with its structurally compact pixel, enable crossbar array-level in-sensor image processing, including edge enhancement and trainable image classification. The results establish a compact organic hardware primitive for low-voltage, reconfigurable, retina-inspired vision systems.

A central challenge for conjugated polymers is to achieve long-range order while remaining solution processable, which is essential for matching the electrical performance of their counterparts of crystalline inorganic semiconductors. In this work, we show that n-doped poly(benzodifurandione) (n-PBDF) can undergo polymerization-driven spontaneous assembly (PSA), in which chain growth, chemical doping, and structural ordering are intrinsically coupled, yielding long-range chain extension over hundreds of nanometers. We reveal that the spontaneously formed n-PBDF nanoribbons arise from a self-initiated, convergent growth mechanism driven by cooperative monomer-polymer interactions and stabilized by proton-coupled duplex chains and the polymer’s intrinsic polyelectrolyte character. With long-range extended chains in the nanoribbons, the aligned n-PBDF thin films demonstrate metallic-level conductivity (>10 ⁴ siemens per centimeter).

Scalable fabrication of uniform perovskite films is a critical bottleneck for large-area perovskite light-emitting diodes (PeLEDs), hindered by coffee-ring formation and heterogeneous crystallization upon scaling. Here, we report a multimodal solvent-engineering strategy enabling highly uniform films via ambient blade coating combined with vacuum-assisted solvent evaporation. Incorporating N -methyl-2-pyrrolidone (NMP) and acetonitrile (ACN) into a dimethylformamide (DMF)–based system synergistically modulates evaporation dynamics: It suppresses macroscopic solute segregation through Marangoni flow–induced redistribution, while tuning precursor coordination to regulate nucleation/phase conversion and promote radiatively efficient film formation. Consequently, the ternary formulation yields films with improved uniformity, reduced trap densities, and enhanced radiative efficiency. Near-infrared (NIR) PeLEDs achieve peak external quantum efficiencies of 25.2% (10 mm ² ), 22.1% (60 mm ² ), and 19.0% (224 mm ² ). A functional vein-imaging prototype is also demonstrated using a 224-mm ² device, highlighting the impact for large-area optoelectronic applications.

Here we report high-performance all-polymer transparent heaters based on the air-stable n-doped polymer poly(benzodifurandione) (n-PBDF). Using a scalable ethanol-based ink and a single-step, post-treatment-free spray-coating process, the resulting films combine low sheet resistance (Rs ≈ 60 Ω sq.–1), high visible light transmittance (VLT > 80%), and low optical haze (85% of their initial performance after 7 days of continuous operation and withstand 60 000 bending cycles (10 mm radius), demonstrating both robust operational stability and mechanical durability. Finally, we demonstrate practical utility by rapid deicing of surface frost on glass-substrate heaters cooled on dry ice (−78.5 °C), and by integrating heaters fabricated on flexible PET substrates into ski goggles and motorcycle visors to enable rapid, low-voltage defogging.

High-performance microphotodetectors require materials that combine strong light–matter interaction, fast charge transport, and ambient stability. Here, we demonstrate single-nanowire devices based on the 2D perovskite (TPA3)₂PbBr₄, synthesized via a controlled slow-cooling self-assembly process that yields defect-minimized, anisotropic nanowires with smooth facets. These microphotodetectors exhibit ultralow dark currents (∼10^–15 A), high responsivity (up to 156 mA W^–1), and exceptional specific detectivity (∼10¹¹ Jones) under near-UV (405 nm) illumination, with rise and fall times in the millisecond regime. The superior detectivity is primarily driven by the suppression of thermal noise through the material’s ultralow dark current, while the millisecond temporal response is governed by high-intensity trap-filling dynamics. The devices maintain stable operation over 4000 s of continuous on/off cycling and show remarkable ambient stability over weeks, attributed to dense crystal packing and robust organic cation layers. Furthermore, the influence of nanowire thickness on the charge collection efficiency is systematically elucidated through optical penetration depth analysis, highlighting design principles for optimizing low-dimensional perovskite photodetectors. This study introduces single 2D perovskite nanowires as a versatile platform for miniaturized, high-performance optoelectronic devices.

Biocompatible integration of synthetic materials with living tissue remains a major challenge for bioelectronics. In this case, substrate-free conducting polymer (CP) interfaces could help bridge this gap. We report in vivo assembly of n-doped poly(benzodifurandione) (n-PBDF) using whole blood–catalyzed polymerization in awake zebrafish and mice. This approach leverages endogenous catalysts, specifically hemoproteins, to form stable, thermally and ionically sensitive CP networks, ensuring long-term compatibility throughout the lifespan. We showcase the impact of this interface through reversible, cellular, and subcellular neuromodulation using near-infrared (NIR) light, including in vivo polymerized n-PBDF. Electrophysiological studies confirmed that n-PBDF alters intrinsic sodium ion channel excitability, and NIR light stimulation amplifies this modulation through thermoionic-induced shunting, providing on-demand, millisecond-scale reversible inhibitory control of excitability, a feature recapitulated in actively behaving mice.

Electrochromic polymers (ECPs) offer promising applications in dynamic optical devices, but their operational stability is often compromised under overpotential stress. Here, we introduce a transparent, highly conductive interlayer of n‐doped poly(benzodifurandione) (n‐PBDF) between indium tin oxide and a representative 3,4‐propylenedioxythiophene based ECP‐Blue (ECP‐B). In its doped state, n‐PBDF is highly conductive, lowering interfacial resistance and supporting rapid charge injection. Upon de‐doping near +0.8 V, it transitions into a resistive barrier that restricts excessive charge flow. Charge density measurements further highlight this protective role as single‐layer ECP‐B accumulates ∼1.49 mC cm ⁻² more charge than the bilayer at +1.5 V, reflecting uncontrolled overoxidation, whereas the n‐PBDF/ECP layer suppresses it. Long‐term cycling confirms that ECP‐B loses redox activity under stress, while the bilayer retains the ECP‐B onset with a broadened n‐PBDF feature. Electrochemical impedance spectroscopy validates this voltage‐gated mechanism, showing low resistance at operational bias, a sharp rise (∼60%) during n‐PBDF de‐doping, and a resistive‐to‐capacitive transition above +1.2 V. Thin‐films spectroelectrochemistry indicates that the bilayer maintains optical contrast comparable to ECP‐B across the operating window and, under overpotential, limits additional loss, preserving ∼50% at +1.5 V.