Transparent p-type CuI film based self-powered ultraviolet photodetectors with ultrahigh speed, responsivity and detectivity

Currently, ultraviolet photodetectors attract extensive attention from people all over the world due to their applications in solar ultraviolet radiation detection, flame detection, ozone monitoring, missile tracking, and environmental monitoring. A heterojunction is an essential aspect for fulfilling the demand for high-performance self-powered ultraviolet photodetectors. However, it is still very challenging to achieve both good electrical property and transparency for p-type semiconductors and conductors especially at low preparation temperature. This work reports the fabrication of ultrathin, ultra-high-transparency and very smooth CuI films at room temperature by the copper film iodination method, whose figure of merit (FoM) far exceeds those of most of the typical p-type oxides. The obtained p-type CuI films (p-CuI) were fabricated on an n-type Si (n-Si) substrate to construct a heterojunction photodetector. The p-CuI/n-Si photodetector has excellent optoelectronic properties in self-powered mode, including a large responsivity and detectivity (123.3 mA W−1, 5.7 × 1012 Jones), and a fast response speed (rise/decay time of 90 μs/140 μs), which are overall better than those of all types of CuI-based self-powered photodetectors. In addition, the CuI film deposited on the flexible substrate was applied in a CuI photodetector with a metal–semiconductor–metal structure, exhibiting good optoelectronic properties and bending stability, which shows promising applications in transparent, flexible, wearable electronic and optoelectronic devices.