Organic Iono-Optoelectronics: From Electrochromics to Artificial Retina

Organic mixed ionic electronic conductors (OMIECs) represent an exciting and emerging class of materials that have recently revitalized the field of organic semiconductors. OMIECs are particularly attractive because they allow both ionic and electronic transport while retaining the inherent benefits of organic semiconducting materials such as mechanical conformability and biocompatibility. These combined properties make the OMIECs ideal for applications in bioelectronics, energy storage, neuromorphic computing, and electrochemical transistors for sensing. Within the realm of OMIECs, a subset of materials and devices known as organic iono-optoelectronics (OIOEs) further leverage the optoelectronic properties of organic semiconductors and functions based on ionic–electronic–photonic interactions. Ionic–electronic coupling can regulate the bandgap of organic semiconducting materials, allowing the tuning of optical properties, which forms the basis for organic electrochromic technology. Additionally, light, as a form of energy, can modulate ionic–electronic coupling, enabling applications such as machine vision and artificial retina.

Among these applications, organic electrochromic devices have demonstrated their practical and commercial value due to their rapid, high-contrast color switching capabilities and potential for cost-effective mass production and roll-to-roll manufacturing. Ambilight Inc. has spearheaded this technology, introducing the first organic electrochromic sunroof product, now used in hundreds of thousands of vehicles. Despite these promising advancements, organic electrochromic devices face several challenges. These include achieving optical contrast higher than 90%, improving color switching speed to meet the demands of dynamic display applications, and enhancing durability to ensure stability in extreme environmental conditions, such as prolonged exposure to sunlight. Growing research on light-modulated ionic–electronic coupling suggests that this fundamental process can be used to mimic the ion-flux-dependent light-capturing processes found in biological retina systems, offering a promising approach for constructing future artificial retina (vision). The intrinsic softness and biocompatibility of the OIOEs further enhance the potential of the artificial retina to interface with biological systems for applications in biomedical optoelectronics and human–machine interfaces. Compared to electrochromic technology, artificial retinas and biomedical optoelectronics are still in their infancy. In this Account, we use two representative technologies─electrochromic devices and artificial retina─to introduce the fundamental processes, advancements, and challenges in the field of OIOEs. We begin with an overview of the fundamental processes shared by and unique to these two technologies. Next, we discuss their respective challenges and the approaches taken by our group and others to improve their performance. Finally, we suggest future research directions. We hope this Account will introduce readers to these fascinating materials and devices and inspire further interest in these research areas.