There has many reasons for the interest in OPVs when comparing the technology to the silicon-based photovoltaics (PV) and interestingly the two very different technologies are complementary in the many ways. The best energy-conversion efficiency published for small-area devices approaches 6%. Key factors are open circuit voltage (Voc), short circuit current(Jsc) and fill factor (FF) which are related with solar cell efficiency. One of the ways to enhance the efficiency is to use electron-donor polymers that can absorb more portion of the solar spectrum. There has been increasing interest in developing low band gap polymers that can lead to increased over lap between their absorption spectra and the solar spectrum, resulting in the increase in the Jsc of the resultant solar cells.This research has focused on development of a new low band gap polymer based on selenophene and benzothiadiazole. Selenophene is a heavy homologue of the series of chalcogenophene and exhibits chemical and physical properties that are similar to those of thiophene. But polyselenophene and oligoselenophene have been little studied due to their low solubility and lack of suitable synthetic methods and reagents.Selenophene and benzothiadiazole based copolymers were synthesized using Suzuki coupling reaction and characterizied by ¹H-NMR, GPC, thermal analyses(TGA), UV-vis spectroscopy, Cyclic Voltammetry(CV), and Organic Photovoltaic device.Poly[4-(5-(5'-methyl -2,2'-biselenophene-5-yl)-4-octylthiophene-2-yl)-7-methyl-4-octylthiophene-2--yl)benzo[2,1,3]thiadiazole] [P1], Poly[4-(5-(5'-methyl -2,2'-biselenophene-5-yl)-4-dodecylthiophene-2-yl)-7-methyl-4-dodecylthiophene-2--yl)benzo[2,1,3]thiadiazole] [P2] were soluble in common organic solvent such as chloroform, chlorobenzene, THF, Toluene. These polymers found to exhibit thermal stability at 300℃, by TGA under a nitrogen atmosphere. The polymers band gap were estimated from UV-vis spectroscopy, Cyclic voltammetry to 1.56eV[P1], 1.59eV[P2] respectively.The bulk hetero-junction solar cell were fabricated with polymers : PCBM(active layer) [ITO/PEDOT:PSS/polymer:PCBM/LiF/Al]. The Jsc, Voc, and FF of the devices[P1,P2] estimated to be 1.04, 1.75mA/cm², 0.6, 0.57V, and 0.27, 0.57 respectively, which correspond to power conversion efficiency of 0.17%[P1], 0.36%[P2] under AM 1.5 illumination of 100mW/cm². The low efficiency of devices were attributed to the low photocurrent of the polymers, due to low absorption of polymers and lack of polymers:PCBM blending.