Gang Chen

Doping to control carrier (electron or hole) transport is foundational to modulate the properties of semiconductors, enabling the development of homojunctions and heterojunctions for integrated electronics. Unlike semiconductors with unipolar charge-carrier dominance, both cations and anions in electrolytes are mobile, which is undesirable for many applications. Here, we report a universal strategy to dope electrolytes such that the ion transport can be unipolar by incorporating electroactive polymers within hydrogels that interact discriminately with one type of ion via redox and binding mechanisms, leaving the counterions mobile. This transforms the system into an active, selective conductor that directs ion flow with high precision. We demonstrate the generality of this strategy using a wide range of electroactive polymers and ions. Particularly, we use emeraldine base and leucoemeraldine base, derived from polyaniline to create both n-type and p-type conductors with high ion selectivity. This electrolyte doping strategy has significant implications beyond the developed thermoelectrochemical devices with boosted performance, with potential applications in supercapacitors, batteries, and electrochemical sensors.

A scalable transparent radiative cooling film for vehicles can reduce the cooling load by 20% and cut annual carbon emission by 25.4 megatons of CO ₂ , equivalent to removing over 5 million gasoline cars from the road.

Lyophilization (aka freeze drying) is a typical process in (bio)pharmaceutical manufacturing used for improving the stability of various drug products, including its recent applications to mRNA vaccines. While extensive efforts are dedicated to shifting the (bio)pharmaceutical industry toward continuous manufacturing, the majority of industrial‐scale lyophilization is still being operated in batch mode. This article presents the first mechanistic model for a complete continuous lyophilization process, which comprehensively incorporates and describes key transport phenomena in all three steps of lyophilization, namely freezing, primary drying, and secondary drying. The proposed model considers the state‐of‐the‐art lyophilization technology, in which vials are suspended and move continuously through the process. The validated model can accurately predict the evolution of critical process parameters, including the product temperature, ice/water fraction, sublimation front position, and concentration of bound water, for the entire process. Several applications related to model‐based process design and optimization of continuous lyophilization are also demonstrated. The final model is made available as an open‐source software package that can be leveraged for guiding the design and development of future continuous lyophilization processes.

Efficient thermal management is essential for the reliability of modern power electronics, where increasing device density leads to severe heat dissipation challenges. However, in thin-film systems, thermal transport is often compromised by interfacial resistance and microscale defects introduced during synthesis or transfer, which are difficult to characterize using conventional techniques. Here we present a non-contact, spatiotemporal-resolved ultrafast x-ray diffraction method to extract in-plane thermal conductivity and thermal boundary conductance, using GaN thin films on silicon as a model system. By tracking the pump-induced lattice strain, we reconstruct the lateral heat flow dynamics and quantitatively probe thermal transport near a wrinkle defect. We uncover pronounced asymmetric heat dissipation across the wrinkle, with a four-fold reduction in the local thermal conductivity near the wrinkle and a 25% drop in interfacial conductance. Our work demonstrates that ultrafast x-ray diffraction can serve as a precise thermal metrology tool for characterizing heat transport in multilayered thin-film structures for next-generation microelectronic devices.

The physics and scaling of thermally driven 3D solar interfacial-evaporators are analyzed. 3D evaporators in an open system can exceed the solar-thermal limit nominally by absorbing environmental heat but cannot do so in a closed solar still.

Evaporation rates from porous evaporators under sunlight have been reported to exceed the solar-thermal limit, determined by relating the incoming solar energy to the latent and sensible heat of water, for applications in desalination and brine pond drying. Although flat two-dimensional (2D) evaporators exceeding the solar limit implies a non-thermal process, tall three-dimensional (3D) solar evaporators can exceed it by absorbing additional environmental heat into its cold sidewalls. Through modeling, we explain the physics and identify the critical heights in which a fin transitions from 2D to 3D evaporation and exceeds the solar-thermal limit. Our analyses illustrate that environmental heat absorption in 3D evaporators is determined by the ambient relative humidity and the airflow velocity. The model is then coarse-grained into a large-scale fin array device on the meters scale to analyze their scalability. We identify that these devices are unlikely to scale favorably in closed environment settings such as solar stills. Our modeling clearly illustrates the benefits and limitations of 3D evaporating arrays and pinpoints design choices in previous works that hinder the device's overall performance. This work illustrates the importance in distinguishing 2D from 3D evaporation for mechanisms underlying interfacial evaporation exceeding the solar-thermal limit.

Cloud absorption is acknowledged as the biggest source of uncertainty in the climate models. For over 70 years, many experiments have reported clouds absorbing more solar radiation than theory could predict. In the visible spectrum, simulations based on optical constants of water lead to negligible cloud absorption. This result had been explored by some experimentalists to calibrate the cloud absorption measurements. However, the author and his collaborators recently discovered that visible light can directly cleave off water molecular clusters at liquid-air interfaces (PNAS, e2312751120, 2023; e2320844121, 2024), which is named the photomolecular effect in analogy to the photoelectric effect. This discovery suggests that a crucial piece of physics has been missing in the existing theories: light can be absorbed at water-air interface. The photomolecular effect can be simulated by generalizing the boundary conditions for the Maxwell equations using Feibelman parameters that were derived in the past research on the surface photoelectric effect and surface plasmons. In this work, the author uses simulation to show that including the photomolecular effect at the air-water interface can potentially explain the cloud absorption anomaly. Although the lack of accurate Feibelman parameter values prevents a direct comparison of the current theory with experiments, this work points to an unexplored mechanism for explaining the cloud absorption anomaly and calls for further investigation on the impacts of photomolecular effect in the climate modeling.