Indium Selenide (InSe) is one of atomically layered 2D materials attracting broad interests recently, because of its good optoelectronic properties. Based on the challenges of 2D optoelectronics, several topics will be covered in this defense, such as trap states and low absorption rate. InSe is selected as a platform to study these topics. The localized states and trap states in InSe system was characterized through low temperature photocurrent measurement to reveal the evolution of band structure and origin of the localized states in few layered InSe. It is found the surface electron orbitals contribute to the localized states. By modifying the surface electron via metallic ions, the Fermi level can be tuned significantly and the inertia surface of the pristine 2D surface can be sensitized for functionalization. Via this method, the InSe photodetector can be improved by organic photosensitive molecules. On the other hand, local gating can induce trap states in 2D materials, helping to improve the photoresponse, but slowing down the response speed. By utilizing this effect, 2D charge coupled device can be fabricated to serve as flexible image sensor which can help correct the optical aberration. The discussion is based on InSe, however, the principle is very universal that can be easily apply to other 2D system. The research can help to promote the research and device development in 2D optoelectronics.