Strategies to break the trade-off between infrared transparency and conductivity

Transparent conductive materials (TCMs) have important applications in the fields of military, biomedicine, and energy. Despite the emergence of visible TCMs, the development of infrared TCM is still a daunting challenge due to the trade-off between infrared transparency and conductivity. This greatly limits the development of next-generation infrared electromagnetic shielding, infrared photodetectors and infrared light-emitting diodes. In this review, we first analyze the fundamental physics of infrared transparency and conductivity to reveal the origin of the trade-off. We then summarize the effect of defect introduction, energy band modulation and surface modification on the performance improvement of traditional infrared TCMs. On this basis, we predict two infrared TCMs: high-εopt heavy-metal chalcogenides and low-n yet high-τ topological semimetals. Finally, we present emerging applications of infrared TCMs and predict future developments. This review, therefore, achieves a coherent description from the physical origin, material design to potential applications, and lays out a roadmap for the development of infrared optoelectronics. This may lead to more researches in the advanced materials, information, energy, and biological communities.