Effect of Polymer Structure and Composition on Photovoltaic Performance of Organic Conjugated Polymer Bulk Heterojunction Solar Cells
| dc.contributor.advisor | Yohannes, Teketel (Professor) | |
| dc.contributor.author | Adam, Getachew | |
| dc.date.accessioned | 2021-01-28T07:35:13Z | |
| dc.date.accessioned | 2023-11-09T16:18:41Z | |
| dc.date.available | 2021-01-28T07:35:13Z | |
| dc.date.available | 2023-11-09T16:18:41Z | |
| dc.date.issued | 2012-06-05 | |
| dc.description.abstract | In this thesis solar energy to electrical energy conversion using organic conjugated polymer based bulk heterojunction solar cells has been studied by aiming at the effect of polymer structure and composition on minimizing the limitations such as lower charge carrier mobility, narrow absorption spectrum, poor nanomorphology of these solar cells which improves the photovoltaic performance in such a way that: a) By random distribution of segments of linear octyloxy side chains, inducing ordering, and of branched 2-ethylhexyloxy side chain, inducing disorder on the backbone of anthracene containing poly(phenylene-ethynylene)-alt-poly (phenylene-vinylene) (PPE-PPV) a side chain based statistical copolymer, denoted AnE-PVstat, has proven to be very effective in terms of field independent higher intrinsic charge carrier mobility μ = 5.43 × 10-4 cm2/Vs demonstrated by CELIV that might be due to its highest --stacking distance of d= 0.393 nm and conformationally balanced morphology as compared to the well-defined congeners. The random combination of the underlying constitutional units seems to promote the side chain geared order and disorder enabling effective tuning of the nanoscale morphology of photoactive layer. Power conversion efficiency up to 3.77% in a bulk heterojunction photovoltaic system and a significant device performance in solid state photoelectrochemical solar cells made using AnEPVstat: PCBM as a photoactive active layer in an open air showing an openOrganic conjugated polymer bulk heterojunction solar cells iv circuit voltage of 320 mV is the present state-of-art value for PPV based materials. b) A 1:1 mixture of two thiophene based poly(p-phenylene-ethynylene)-alt-poly(pphenylene- vinylene)s denoted DO-PThE1-PPV2 (D1) and MEH-PThE1-PPV2 (D2), consisting of the same conjugated backbone but different types and volume fraction of alkoxy side chains on the phenylene-ethynylene unit, has lead to enhanced charge carrier mobility as compared to the individual polymers. The resulting ternary blend with PCBM showed better photovoltaic performance as compared to binary blends. This is due to improved active layer nanomorphology in the ternary system as revealed by AFM studies. c) By varying one moiety with thiophene, bithiophene or 3,4-ethylenedioxy thiophene at the X position in the thiophene containing poly(p-phenyleneethynylene)- alt-poly(p-phenylene-vinylene)s (PPE-PPV) copolymers with a general structural design (Ph-CC-X-CC-Ph-CH=CH-Ph-CH=CH-) bearing identical side chains at the phenylene rings were synthesized. The effect of this structural alteration on the properties such as photophysics, electrical, charge carrier mobility and morphology of the materials and its impact on their photovoltaic performance were studied. The copolymer with a single thiophene ring at the X positions showed the highest VOC of 930 mV and the copolymer with a bithiophene unit at X position showed the highest short-circuit current density and charge carrier mobility. Where as the copolymer with 3,4-ethylenedioxy thiophene showed the lowest photovoltaic performance. d) To change the structure of the polymer by doping, a 1:1 ratio of Poly(3- hexylthiophene) (P3HT) to [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was dissolved in chlorobenzene containg four different molar concentrations of Organic conjugated polymer bulk heterojunction solar cells v the dopant ferric chloride. The photophysical properties in solution as well as in their films were characterized using Uv-Vis absorption and bulk hetrojunction solar cell devices were fabricated from each solution were characterized. It was found that with increasing the dopant concentration, monochromatic photocurrent spectra and IPCE of the devices showed a red shift which is consistent with the optical absorptions and the instu spectroelectrochemical behavior of P3HT. By doping the short circuit current of the devices increased due to an increase in charge carrier mobiliy. It was also observed that the best photovoltaic performance was achieved at lower concentration of FeCl3 as compared to undoped devices used in this experiment. e) A ternary blend of two polymers poly(3-hexylthiophene) and poly[4,4-bis(2- ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b]dithiophene-2,6-diyl-alt-4,7-bis(2-thienyl )-2,1,3-benzothiadia-zole-5’,5’’-diyl] (PCPDTTBTT) with complementary absorption and an acceptor [6,6]-phenyl C61-butyric acid methyl ester (PCBM) were used to fabricate the bulk hetrojunction type solar cells inorder to increase (broadening) the absoprption in the visible spectrum. It was found that the ternary blend showed better absorption spectrum as evidenced from the optical absorption, photocurrent spectra and IPCE curves of the blend. Due to this increased absorption of light the ternary blend has shown improved short circuit current and open circuit voltage due to n-type behaviour of PCPDTTBTT as compared to the binary blends of each polymer with PCBM. | en_US |
| dc.identifier.uri | http://etd.aau.edu.et/handle/12345678/24868 | |
| dc.language.iso | en | en_US |
| dc.publisher | Addis Ababa University | en_US |
| dc.subject | Effect of Polymer | en_US |
| dc.subject | Structure | en_US |
| dc.subject | Composition on Photovoltaic | en_US |
| dc.subject | Performance | en_US |
| dc.subject | Organic Conjugated | en_US |
| dc.subject | Polymer Bulk | en_US |
| dc.subject | Heterojunction Solar Cells | en_US |
| dc.title | Effect of Polymer Structure and Composition on Photovoltaic Performance of Organic Conjugated Polymer Bulk Heterojunction Solar Cells | en_US |
| dc.type | Thesis | en_US |