Open-shell radicals have received a lot of attention due to its potential applications in highly efficient photothermal conversion and therapy. However, it is challenging to enhance the chemical and photothermal stability of the open-shell structure. Herein, a stable open-shell poly(3,4-dioxythiophene) radical PTO2 was readily synthesized via simple BBr3-demethylation of the copolymer P(TOMe2-EDOT) precursor using low-cost materials. The open-shell character of PTO2 was confirmed by the highly enhanced electron spin resonance signal comparing with P(TOMe2-EDOT). Interestingly, the powder of PTO2 exhibit extremely wide absorption range between 300 and 2500 nm, which is comparable with those of graphene and Fe3O4. Under the same irradiation of 1.2 W cm-2, the powder of PTO2 can reach 242 ℃ which is much higher 200 ℃ of the P(TOMe2-EDOT). The decreased photothermal conversion capability of the metal-ionized PTO2 complexes indicates that the radical structure of the polymer has a significant effect on the photothermal conversion properties. To date, PTO2 stands as one of the low cost pure organic photothermal materials with super-high photothermal conversion performances.