Designing bismuth selenide/metal/bismuth selenide thin films to realize the integration of mid- to far-infrared transparency and conductivity

•Bismuth selenide is used as a dielectric material to construct a sandwich structure.•The first infrared transparent conductive film in sandwich structure is developed.•Sandwich-structure film has better optoelectronic properties than bismuth selenide. Designing semiconductor/metal/semiconductor (SMS) sandwich structure film is an effective way to combine transparency and conductivity. However, traditional SMS mainly uses metal oxides such as ITO as the semiconductor material, which can only achieve transparency and conductivity in the visible to near-infrared band, but not in the mid-to far-infrared (MFIR) band. Here, we use bismuth selenide as semiconductor material and Ti as metal to construct SMS and achieve excellent MFIR transparent conductive properties. The results show that the conductivity of the SMS is increased by 3.8 times compared with the bismuth selenide, with only 3% decrease in the transmittance in 8–12 μm. Therefore, this study proposes a new material design strategy to solve the bottleneck problem of integrating MFIR transparency and conductivity.