New n-doped transparent conductor shows promise for all-polymer electrochromic displays

Recent technological advances have enabled the development of increasingly sophisticated and energy-efficient displays for electronic devices. To further improve existing displays and create even more efficient ones, some engineers have been trying to synthesize and identify new materials with promising opto-electronic properties.

A research team at Purdue University has synthesized a transparent conducting polymer dubbed n-doped poly(benzodifurandione) (n-PBDF), which could be used to develop more sustainable and efficient electrochromic displays. This polymer, introduced in a paper published in Nature Electronics, was used to fabricate a display that exhibits low power consumption, bistability (i.e., the ability to maintain a pixel’s visual state without requiring continuous power supply) and full-color capabilities.

“This study emerged from a pressing need to develop energy-efficient and human-friendly display technologies that mitigate the drawbacks of traditional emissive displays, such as high energy consumption and eye strain,” Jianguo Mei, senior author of the paper, told Tech Xplore. “The inspiration lay in exploring electrochromic displays, which operate through natural light transmission/reflection rather than light emission.”

Building on recent studies assessing the potential of electrochromic displays, Mei and his colleagues set out to synthesize a new material that could be used to fabricate these displays. This led to the synthesis of n-PBDF, a transparent conducting polymer that can serve both as a conductor and ion-storage material.

“This polymer serves dual roles as a transparent conductor and ion-storage material, enabling the fabrication of flexible, all-polymer electrochromic displays with simplified device architectures and low power consumption,” explained Mei.

The researchers carried out a series of tests aimed at testing the potential of the polymer they created. First, they carried out experiments that assessed its capacitance, by measuring its charge storage capability using two techniques known as cyclic voltammetry (CV) and optical transmittance.

“We then created electrochromic displays where n-PBDF acted as both the transparent conductor and the ion-storage layer,” said Mei. “In addition, we performed durability tests, to evaluate its performance under varying environmental conditions (i.e., humidity, temperature, etc.) and long-term electrochemical cycling.”

To synthesize n-PBDF, the researchers used solution processing, a technique that is widely used in the fabrication of printed electronics. Using solution processing allowed them to produce highly transparent and flexible films, which they could easily incorporate in displays.

The new polymer they synthesized combines good ionic and electronic conductivity. Unlike indium tin oxide (ITO), which is traditionally used to create touch screens and displays, n-PBDF is highly flexible and solution processable.

Moreover, the new polymer can simplify a display’s architecture, by reducing the number of layers it contains. The researchers had already used it to create a chromodynamic display that performed remarkably well, attaining a low power consumption and good color rendition.

“We found that n-PBDF successfully replaces conventional materials like ITO by combining transparency, conductivity, and ion-storage in one layer,” said Mei.

“Using this material, we also demonstrated a flexible, full-color, all-polymer electrochromic display with low power consumption (0.7 μW/cm² for static content) and bistability for up to 24 hours without power.”

Notably, the new polymer developed by this research team performs well under environmental stress and can easily be fabricated on a large scale using photolithography, which could contribute to its widespread adoption. In the future, it could also be used to develop energy-efficient displays for wearable electronics or foldable devices.

“In the near future, we plan to work on enhancing the coating quality of n-PBDF films for better uniformity and scalability,” added Mei.

“We will also investigate their compatibility with diverse electrochromic materials for broader applications. As a long-term goal, we hope to expand the use of n-PBDF in other electronic and optoelectronic devices, such as super capacitors, batteries, solar cells and organic LEDs. Moreover, we plan to develop advanced encapsulation methods to further improve the environmental stability of displays.”

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