Low‐Temperature Fabrication and Performance of Polycrystalline CuI Films as Transparent p‐Type Semiconductors

Transparent p‐type polycrystalline CuI films with high hole mobility are produced by solid iodination of Cu 3 N precursor layers and subsequent heat treatment at 120 °C. The hole mobility reached 20 cm 2 V −1 s −1 in the CuI films fabricated on both glass and polyethylene terephthalate substrates. Furthermore, transparent p–n diodes with sufficiently high rectification ratio (6 × 10 6 ) and ideality factor (1.6) are successfully fabricated by employing a heterojunction of p‐type CuI and n‐type amorphous In–Ga–Zn–O (a‐IGZO) layers. The CuI/a‐IGZO heterojunction exhibits the photovoltaic effect, with a short‐circuit current of 0.33 µA and an open‐circuit voltage of 10 mV under UV illumination at a wavelength of 365 nm and intensity of 1.9 mW cm −2 . The photoresponse at zero bias is sufficiently quick, and thus, the photovoltaic properties of the CuI/a‐IGZO diodes rendere them potential candidates for visible‐light‐blind and self‐powered UV photodetectors. These findings suggest that CuI is an excellent transparent p‐type semiconductor that can be fabricated at low temperature.