A highly π-extended copolymer, PPTT, was developed based on 6H-phenanthro[1,10,9,8-cdefg]carbazole (PCZ) and thiazolo[5,4-d]thiazole derivative units, being the first PCZ-containing polymer, as well as its first applications in OTFTs and OPVs. This polymer exhibited an excellent solubility in several common organic solvents, a good film-forming ability, a reasonably high thermal stability, and a deep-lying HOMO energy level, meeting well the requirements of OTFTs and OPVs. The investigation of the field-effect and photovoltaic performances demonstrated that PPTT had a high hole mobility of 0.13 cm² V⁻¹ s⁻¹ and good power conversion efficiency (PCE) of 3.20%, which were among the highest mobilities and PCEs for a single polymer material with dual transistor and OPV functions simultaneously.