In this thesis solar energy to electrical energy conversion using organic conjugatedrnpolymer based bulk heterojunction solar cells has been studied by aiming at the effectrnof polymer structure and composition on minimizing the limitations such as lowerrncharge carrier mobility, narrow absorption spectrum, poor nanomorphology of thesernsolar cells which improves the photovoltaic performance in such a way that:rna) By random distribution of segments of linear octyloxy side chains, inducingrnordering, and of branched 2-ethylhexyloxy side chain, inducing disorder on thernbackbone of anthracene containing poly(phenylene-ethynylene)-alt-polyrn(phenylene-vinylene) (PPE-PPV) a side chain based statistical copolymer, denotedrnAnE-PVstat, has proven to be very effective in terms of field independent higherrnintrinsic charge carrier mobility Î¼ = 5.43 Ã— 10-4 cm2/Vs demonstrated by CELIVrnthat might be due to its highest ï°-ï°-stacking distance of dï°ï°ï€ = 0.393 nm andrnconformationally balanced morphology as compared to the well-definedrncongeners. The random combination of the underlying constitutional units seemsrnto promote the side chain geared order and disorder enabling effective tuning ofrnthe nanoscale morphology of photoactive layer. Power conversion efficiency up torn3.77% in a bulk heterojunction photovoltaic system and a significant devicernperformance in solid state photoelectrochemical solar cells made using AnEPVstat:rnPCBM as a photoactive active layer in an open air showing an openOrganicrnconjugated polymer bulk heterojunction solar cellsrnivrncircuit voltage of 320 mV is the present state-of-art value for PPV basedrnmaterials.rnb) A 1:1 mixture of two thiophene based poly(p-phenylene-ethynylene)-alt-poly(pphenylene-rnvinylene)s denoted DO-PThE1-PPV2 (D1) and MEH-PThE1-PPV2rn(D2), consisting of the same conjugated backbone but different types and volumernfraction of alkoxy side chains on the phenylene-ethynylene unit, has lead tornenhanced charge carrier mobility as compared to the individual polymers. Thernresulting ternary blend with PCBM showed better photovoltaic performance asrncompared to binary blends. This is due to improved active layer nanomorphologyrnin the ternary system as revealed by AFM studies.rnc) By varying one moiety with thiophene, bithiophene or 3,4-ethylenedioxyrnthiophene at the X position in the thiophene containing poly(p-phenyleneethynylene)-rnalt-poly(p-phenylene-vinylene)s (PPE-PPV) copolymers with arngeneral structural design (Ph-Cï‚ºC-X-Cï‚ºC-Ph-CH=CH-Ph-CH=CH-) bearingrnidentical side chains at the phenylene rings were synthesized. The effect of thisrnstructural alteration on the properties such as photophysics, electrical, chargerncarrier mobility and morphology of the materials and its impact on theirrnphotovoltaic performance were studied. The copolymer with a single thiophenernring at the X positions showed the highest VOC of 930 mV and the copolymer withrna bithiophene unit at X position showed the highest short-circuit current densityrnand charge carrier mobility. Where as the copolymer with 3,4-ethylenedioxyrnthiophene showed the lowest photovoltaic performance.rnd) To change the structure of the polymer by doping, a 1:1 ratio of Poly(3-rnhexylthiophene) (P3HT) to [6,6]-phenyl-C61-butyric acid methyl ester (PCBM)rnwas dissolved in chlorobenzene containg four different molar concentrations ofrnOrganic conjugated polymer bulk heterojunction solar cellsrnvrnthe dopant ferric chloride. The photophysical properties in solution as well as inrntheir films were characterized using Uv-Vis absorption and bulk hetrojunctionrnsolar cell devices were fabricated from each solution were characterized. It wasrnfound that with increasing the dopant concentration, monochromatic photocurrentrnspectra and IPCE of the devices showed a red shift which is consistent with thernoptical absorptions and the instu spectroelectrochemical behavior of P3HT. Byrndoping the short circuit current of the devices increased due to an increase inrncharge carrier mobiliy. It was also observed that the best photovoltaicrnperformance was achieved at lower concentration of FeCl3 as compared tornundoped devices used in this experiment.rne) A ternary blend of two polymers poly(3-hexylthiophene) and poly[4,4-bis(2-rnethylhexyl)-4H-cyclopenta[2,1-b:3,4-bï€²]dithiophene-2,6-diyl-alt-4,7-bis(2-thienylrn)-2,1,3-benzothiadia-zole-5â€™,5â€™â€™-diyl] (PCPDTTBTT) with complementaryrnabsorption and an acceptor [6,6]-phenyl C61-butyric acid methyl ester (PCBM)rnwere used to fabricate the bulk hetrojunction type solar cells inorder to increasern(broadening) the absoprption in the visible spectrum. It was found that the ternaryrnblend showed better absorption spectrum as evidenced from the opticalrnabsorption, photocurrent spectra and IPCE curves of the blend. Due to thisrnincreased absorption of light the ternary blend has shown improved short circuitrncurrent and open circuit voltage due to n-type behaviour of PCPDTTBTT asrncompared to the binary blends of each polymer with PCBM.