Self-powered and flexible ultrabroadband photodetectors (PDs) are desirable in a wide range of applications. The current PDs based on the photothermoelectric (PTE) effect have realized broadband photodetection. However, most of them express low photoresponse and lack of flexibility. In this work, high-performance, self-powered, and flexible PTE PDs based on laser-scribed reduced graphene oxide $(\mathrm{LSG})/{\mathrm{CsPbBr}}_3$ are developed. The comparison experiment with LSG PD and fundamental electric properties show that the $\mathrm{LSG}/{\mathrm{CsPbBr}}_3$ device exhibits enhanced ultrabroadband photodetection performance covering ultraviolet to terahertz range with high photoresponsivity of 100 mA/W for 405 nm and 10 mA/W for 118 μm at zero bias voltage, respectively. A response time of 18 ms and flexible experiment are also acquired at room temperature. Moreover, the PTE effect is fully discussed in the $\mathrm{LSG}/{\mathrm{CsPbBr}}_3$ device. This work demonstrates that $\mathrm{LSG}/{\mathrm{CsPbBr}}_3$ is a promising candidate for the construction of high-performance, flexible, and self-powered ultrabroadband PDs at room temperature.