Solid-state reaction synthesis of a InSe/CuInSe₂ lateral p-n heterojunction and application in high performance optoelectronic devices

Graphene-like layered semiconductors are a new class of materials for next generation electronic and optoelectronic devices due to their unique electrical and optical properties. A p-n junction is an elementary building block for electronics and optoelectronics devices. Here, we demonstrate the fabrication of a lateral p-n heterojunction diode of a thin-film InSe/CuInSe₂ nanosheet by simple solid-state reaction. We discover that InSe nanosheets can be easily transformed into CuInSe₂ thin film by reacting with elemental copper at a temperature of 300 °C. Photodetectors and photovoltaic devices based on this lateral heterojunction p-n diode show a large photoresponsivity of 4.2 A W^-1 and a relatively high light-power conversion efficiency of 3.5%, respectively. This work is a giant step forward in practical applications of two-dimensional materials for next generation optoelectronic devices.