Rui-Tao Wen

Wavelength bandwidth is a key performance metric for emerging optical interconnects targeting high-data-rate communications. Strain engineering has proven effective in tailoring the wavelength bandwidth of Ge photonic devices. Although a recessed SiN sidewall stressor was found to extend the absorption edge of Ge photodetectors (PDs) into the L-band with a responsivity improvement of >3×, the working mechanism of the recessed stressor remains poorly understood. Here, we attribute the strain enhancement and its spatial uniformity improvement in Ge PDs to the removal of the compressive strain at the bottom edge corners of the Ge strip. PDs employing the stressors exhibit electrical responses consistent with the mechanism. These findings offer a general framework for applying recessed SiN sidewall stressors to semiconductor photonic devices.

By minimizing total building energy at each timestep, we establish a paradigm that defines optical targets and operation schemes for electrochromic windows, avoiding control-induced energy penalties and unlocking their energy-saving potential.

Electrochromic devices offer a compelling platform for dynamic control of light and heat, with significant potential for energy‐efficient smart windows and adaptive optoelectronic applications. However, their widespread adoption is critically hindered by the lack of competent anodic materials capable of mitigating charge imbalance between the cathodic and anodic layers. Here, we demonstrate a full charge‐balanced electrochromic design based on a WO ₃ /LiCoO ₂ architecture, enabling highly stable device operation. Unlike the conventional anodic material NiO, which suffers from limited charge capacity and poor reversibility, diffusion‐controlled LiCoO ₂ provides a readily tunable charge storage capability through thickness engineering. In addition, the long‐standing challenge in achieving stoichiometric LiCoO ₂ via magnetron sputtering can be resolved by introducing a lithium‐supplementation strategy. The resulting WO ₃ /LiCoO ₂ devices exhibit both effective privacy control and thermal management, delivering high optical modulation alongside excellent cycling stability. This work establishes a viable pathway toward high‐durability, high‐performance electrochromic devices for smart windows and automotive thermal management applications.

In the article by Huang et al., ‘TT-Nb₂O₅ with dual-band modulation and exceptional performance retention for fast-responsive electrochromics’ (National Science Review, Volume 12, Issue 6, 2025, nwaf154, https://doi.org/10.1093/nsr/nwaf154), the erroneous notation ‘Nb 3d’ was used at page 1, line 23; page 2, line 39; page 4, lines 1 and 5; page 5, line 3, as well as page 9, lines 17 and 22.

The optical properties of electrochromic windows can be modulated by embedding electrons and ions simultaneously to realize energy-saving functions. However, the microscopic electrochromic mechanism in cathode materials remains controversial. Herein, we have discovered that the single-crystal WO₃ nanosheets exhibit thickness-dependent electrochromic characteristics. The multislice electron ptychography experiments revealed that the colour centers in electrochromic WO₃ are associated with lattice distortions, and the density of the colour centers decreases from surface to bulk. Moreover, the heterogeneous distribution of polarons induces a phase transition from monoclinic to tetragonal and cubic structures, which in turn causes the band gap of the WO₃ nanosheets to follow a volcano-type trend. This phenomenon elucidates the colour shift of the electrode from yellow to blue or black as the thickness of the nanosheets decreases. By visualizing the actual colour centers of electrochromic materials, our findings provide an optimal framework for the development of high-performance electrochromic devices.

Electrochromic devices (ECDs), featuring passive optical modulation, backlight-free operation, and bistable low-power characteristics, are promising candidates for energy-efficient display applications. However, wide-gamut color modulation in electrochromic displays is hampered by both the narrow spectral tunability of conventional materials and the fabrication complexity of existing wide‑gamut devices. Herein, we develop an approach to achieving reversible wide-gamut color switching by depositing ellipsoidal metallic nanoparticles and an electrochromic WO3 layer in series. Specifically, the dielectric environment surrounding the metallic nanoparticles is dynamically altered by electrochemically modulating the refractive index of the WO3 layer, enabling precise tuning of the localized surface plasmon resonance absorption peak. As a result, a broad collective color gamut spanning the visible spectrum is achieved through Ag NP dimension engineering. In addition, the Ag nanoparticles (NPs)/WO3 working electrode exhibits a low electrode-level average coloration power density of 4 W m-2. We believe the results demonstrated in this work provide a new strategy for electrochromic display devices.

Precisely controlling structural colours in polymeric materials remains a major challenge, with current approaches often relying on trial-and-error synthesis. Here, we develop a colour design model, enabling inverse design of structural colours in bottlebrush block copolymers (BBCPs). The model can quantitatively link BBCP molecular structures to macroscopic colours through the integration of a strong segregation self-consistent field theory model with a multilayer optical framework. We first validate its predictive capability by synthesising and assembling BBCPs with varied chain architectures to produce a full colour spectrum, and then demonstrate its generalisability to other BBCP chemistries. In addition, we observe reversible, nonlinear thermochromism in systems combining a crystalisable block with a soft, low–glass transition temperature segment, while similar BBCPs lacking this pairing show no such response. Our work establishes a predictive platform for designing structurally coloured, thermoresponsive polymeric materials and advances the rational engineering of photonic soft matter.

A comparative study is presented on the dependence of optical and material properties of VCSELs on Ge and GaAs substrate thicknesses as well as epitaxy process conditions. It was found that adjusting the Ge substrate thickness and optimizing the epitaxy process can shift the stopband center and cavity resonance wavelength by several nanometers. Ge-based VCSELs exhibit improved epitaxial uniformity, smaller deviations from design specifications, reduced stoichiometry variations, and strain magnitudes comparable to those of GaAs-based counterparts. In the selected 46.92 μm² sample area, no defects were observed in the quantum well (QW) regions of Ge-based VCSELs, and the threading dislocation density (TDD) was measured to be below 2.13 × 10⁶ cm⁻². These results highlight the potential of Ge substrates as promising candidates for advanced VCSELs.