Soluble thiophene-based copolymers, poly[(3-alkylthiophene)-co-(3-thiophene acetic acid)]s (P3AT-co-3TAA-n's), were synthesized to apply to the polymer sensitizer of the polymer-sensitized solar cell devices. In order to improve the solubility and the chemical adsorption onto nanoporous TiO2 layers in the polymer-sensitized solar cell devices, thiophene- based copolymers having the chemical structures of the carboxyl group and the alkyl group were designed. We have fabricated solidstate polymer-sensitized solar cell devices using polymer sensitizers and polymer electrolytes, and investigated on the photovoltaic performances. In the polymersensitized solar cell devices using polymer sensitizers, V-OC is 0.37-0.46V, J(SC) is 0.82-7.71mA/cm(2), and the power conversion efficiency is 0.14-0.38%, respectively.