유기태양전지의 효율 향상을 위한 새로운 고분자의 합성 및 광전변환특성에 대한 연구

Abstract

π-conjugated polymer based bulk hetero-junction (BHJ) solar cells have been attracting considerable attention recently due to their unique advantage of low cost, light weight and potential application in flexible large-area devices. The BHJ of π-conjugated polymers (electron donor) blended with fullerene (C60) derivatives (electron acceptor) should boost the efficiency of polymer solar cells. Power conversion efficiency (PCE) up to 5% has been obtained from both the BHJ solar cells of poly(3-hexylthiophene) (P3HT) blended with (6)-1-(3-(methoxycarbonyl)propyl)-{5}-1-1-phenyl-[5,6]-fullerene (PCBM) and one of poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4b]-dithiophene)-alt-4,7-benzo(2,1,3)thiadiazole)](PCPDTBT) blended with PCBM. The BHJ solar cells made from P3HT and PCPDTBT had high fill factor (FF) and short circuit current density (Jsc), while PCE was still limited by 0.60 ~ 0.65 V of lower open circuit voltage (Voc). The mean of increasing Voc is a facile method to improve PCE. Recently, the BHJ polymer solar cell using 4,7-dithiophen-2-yl-benzo(1,2,5)thiadiazole based alternating copolymers such as PFDTBT have demonstrated larger Voc (0.95 ~ 1.04 V), however, their PCE is still low owing to the lower Jsc than that of both P3HT and PCPDTBT based cells. If the Jsc of this type of copolymer based solar cells can be further enhanced while maintaining their large Voc, higher PCE can be expected. Poly[4,7-dithiophen-2-ylbenzo(1,2,5)thiadiazole-alt-1,4-bis(dodecyloxy)-2,5-divinylbenzene] (PPVTBT) and poly[4,7-dithiophene-2-yl-benzo(1,2,5)thiadiazole-alt-dihexyl-9H-fluorene] (PFTBT) based on 4,7-dithiophene-2-yl-benzo(1,2,5)thiadiazole were synthesized using Heck and Suzuki coupling reactions. Poly[2,3-dimethyl-5,8-dithiophene-2-yl-quinoxaline-alt-9,9-dihexyl-9H-fluorene] (PFTQT) and poly[2,3-dimethyl-5,8-dithiophen-2-yl-quinoxaline-alt-10-hexyl-10H-phenothiazine] (PPTTQT) based on 2,3-dimethyl-5,8-dithiophen-2-yl-quinoxaline were synthesized using Suzuki coupling reaction. All polymers were soluble in common organic solvents such as chloroform, chlorobenzene, dichlorobenzene, THF and toluene. The band gap of polymers were estimated UV-Vis spectroscopy and cyclic voltammogram between 1.7 ~ 2.3 eV. The BHJ type photovoltaic cells were fabricated with polymer and PCBM [ITO/PEDOT:PSS/polymer:PCBM/Al]. New polymers were showed broad absorption regions and had proper energy levels. The BHJ type photovoltaic cells were expected to high Jsc and PCE due to the good overlap of solar energy.