▎ 摘　　要

Reduced graphene oxide (rGO) is an attractive candidate for large area photodetectors because of its ultrabroadband absorption, controllable reduction level, ease of material processing, and compatibility with various substrates. However, inefficient separation of photogenerated charge carriers leads to its slow and low responsivity especially for high power intensity light. Here, we present a simple photodetector solely based on a reduced graphene oxide (rGO) thick film as the active material. The role of substrate in the photoresponse mechanism was explored by fully removing the substrate from the rGO film photodetector. The removal of the substrate blocks the cooling pathways for photoexcited carriers under ambient conditions, and greatly increases the photothermoelectric effect. In contrast to previously reported enhancement of responsivity at a single light wavelength by substrate removal, broadband responsivity enhancement of the substrate-free device is achieved from the ultraviolet to near-infrared range by removing the substrate from the rGO film device. Especially, for visible light, the substrate-free photodetector not only demonstrates a responsivity over six times larger than that of the corresponding photodetector with the substrate, but also outmatches the performance of other reported competitors solely based on graphene as the active material at similar levels of light intensity irradiation. For the first time, our work doubtlessly unveils that the substrate significantly affects the photoresponse of rGO devices. This finding offers a new direction towards the future improvement of rGO-based optoelectronic devices.