π-Conjugated polymers composed of dialkoxybenzo[1,2-b:4,5-b′]dithiophene and thiophenes bearing cyano-alkoxycarbonylethenyl [CHC(CO2R)CN] and bis(alkoxycarbonyl)ethenyl groups [CHC(CO2R)2] were prepared. The optical properties of the obtained polymers were investigated by UV-vis and photoluminescence spectroscopy to demonstrate that the absorption maxima of the polymers were tunable by varying the substituent of thiophene unit. The photoluminescence wavelengths and intensities of the polymer in solution were significantly dependent on the polymer side chain. The HOMO energy level of the polymer was lowered by up to −5.51 eV by introducing electron-deficient cyano groups. Polymer solar cells based on the new polymers were fabricated to achieve a PCE of 1.90%.