Due to their unique optical properties, plasmonic materials are widely used in nonlinear optics, nanophotonics, optoelectronics, photocatalysis, biosensing, information storage, etc. Researchers usually need to know the detailed permittivity behavior at the vicinity of surface plasmons’ excitation wavelengths, which in turn are located near the zero points of the real part of the permittivity called epsilon-near-zero (ENZ). We hereby introduce a spectral fitting method to quickly obtain the materials' permittivity at the ENZ region and summarize the experiences of selecting dispersion models and optimizing model parameters. Specifically, we have made a detailed description of the optical constant fitting process for a series of plasmonic materials such as heavily doped semiconductors, transparent conductive oxides, organic conductive materials, two-dimensional materials, and sandwiched composites. Hopefully, to provide specific data and theoretical support for researchers in the field of photoelectric properties of plasmonic materials.

The unique performances of Epsilon-near-zero (ENZ) materials allow them to play a crucial role in many optoelectronic devices and have spawned a wide range of inventive uses. In this paper, we found that the modified PEDOT:PSS film formed with a kind of so-called “Metastable liquid-liquid Contact (MLLC)” solution treatment method can achieve a wide tuning of ENZ wavelength from 1270 nm to 1550 nm in the near-infrared region. We further analyzed the variation trend of imaginary permittivity for these samples with different ENZ wavelengths. The Berreman mode was successfully excited by a simple structural design to realize a tunable polarization absorber.

With commercial electronics transitioning toward flexible devices, there is a growing demand for high‐performance polymers such as poly(3,4‐ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS). Previous breakthroughs in promoting the conductivity of PEDOT:PSS, which mainly stem from solvent‐treatment and transfer‐printing strategies, remain as inevitable challenges due to the inefficient, unstable, and biologically incompatible process. Herein, a scalable fabrication of conducting PEDOT:PSS inks is reported via a metastable liquid−liquid contact (MLLC) method, realizing phase separation and removal of excess PSS simultaneously. MLLC‐doped inks are further used to prepare ring‐like films through a compromise between the coffee‐ring effect and the Marangoni vortex during evaporation of droplets. The specific control over deposition conditions allows for tunable ring‐like morphologies and preferentially interconnected networks of PEDOT:PSS nanofibrils, resulting in a high electrical conductivity of 6,616 S cm−1 and excellent optical transparency of the film. The combination of excellent electrical properties and the special morphology enables it to serve as electrodes for touch sensors with gradient pressure sensitivity. These findings not only provide new insight into developing a simple and efficient doping method for commercial PEDOT:PSS ink, but also offer a promising self‐assembled deposition pattern of organic semiconductor films, expanding the applications in flexible electronics, bioelectronics as well as photovoltaic devices.

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