Colorless-to-colorful switching electrochromic polyimides with very high contrast ratio

Qiang Zhang,Chou-Yi Tsai,Lain-Jong Li,Der-Jang Liaw

doi:10.1038/s41467-019-09054-8

Abstract

Colorless-to-colorful switching electrochromic polymers with very high contrast ratio are unattainable and attractive for the applications of smart wearable electronics. Here we report a facile strategy in developing colorless-to-colorful switching electrochromic polyimides by incorporating with alicyclic nonlinear, twisted structures and adjusted conjugated electrochromophores, which minimize the charge transfer complex formation. It is noted that, by controlling the conjugation length of electrochromophore, the colorless-to-black switching electrochromic polymer film (PI-1a) exhibites an ultrahigh integrated contrast ratio up to 91.4% from 380 to 780 nm, especially up to 96.8% at 798 nm. In addition, PI-1a film with asymmetric structure also demonstrates fast electrochemical and electrochromic behaviors (a switching and bleaching time of 1.3 s and 1.1 s, respectively) due to the loose chain stacking, which provides more pathways for the penetration of counterion. Moreover, the colorless-to-black EC device based on PI-1a reveals an overall integrated contrast ratio up to 80%.

Highlights

Colorless-to-colorful switching electrochromic polymers with very high contrast ratio are unattainable and attractive for the applications of smart wearable electronics
Non-emissive electrochromic polymers (ECPs) received great attention recent decades due to their low-power consumption, facile color tunablility through molecular design[1], high processability of highly flexible and rollable displays compared to their inorganic counterparts[2,3,4,5]
Reynolds et al.[3,5,6] initiated the development of blackto-transmissive ECPs through donor-acceptor design, weak absorption of these fully oxidized ECP films[5] in the visible region still existed. Another strategy was developed by Lee et al and Beverina et al, transmissive-to-black ECPs were obtained by incorporating multichromophores, which had the advantages of superposition of different absorptions from different electrochromophores[8,9,10,11]

Summary

Introduction

Colorless-to-colorful switching electrochromic polymers with very high contrast ratio are unattainable and attractive for the applications of smart wearable electronics. By controlling the conjugation length of electrochromophore, the colorless-to-black switching electrochromic polymer film (PI-1a) exhibites an ultrahigh integrated contrast ratio up to 91.4% from 380 to 780 nm, especially up to 96.8% at 798 nm. The colorless-to-colorful ECPs, especially the colorlessto-black ECPs with ultrahigh contrast ratio over the entire visible region, are still unattainable due to the extreme difficulties in design of completely reverse absorptions (transmittance) in transmissive and colored states[5,6]. Reynolds et al.[3,5,6] initiated the development of blackto-transmissive ECPs through donor-acceptor design, weak absorption of these fully oxidized ECP films[5] in the visible region still existed Another strategy was developed by Lee et al and Beverina et al, transmissive-to-black ECPs were obtained by incorporating multichromophores, which had the advantages of superposition of different absorptions from different electrochromophores[8,9,10,11]. The charge transfer complex (CTC) formation in polyimides always generated yellow or brown colors in polyimide films[25], which may hinder the development of colorless polyimide films

Methods

Results

Conclusion