A ${pi}$-conjugated dialkoxynaphthalene-based donor-acceptor copolymer was synthesized by a Suzuki coupling reaction, and its photophysical, thermal and electrochemical properties and photovoltaic characteristics were characterized. The copolymer showed good solubility and a weight average molecular weight of 11,500. The new copolymer was characterized by two absorption bands at 315 and 403 nm in the dilute solution, which were assigned to the ${pi}{ ightarrow}{pi}^*$ transition and an intramolecular charge transfer band, respectively. The wide band gap of the donor-acceptor copolymer was explained by the 3-dimensional structure and tortional angle between the dialkoxynaphthalene and benzothiadiazole of the model compound. The PCE of the photovoltaic solar cell device fabricated using this copolymer reached 0.06% with a $V_{oc}$, $J_{sc}$ and FF of 0.59, 0.3, and 33%, respectively.