| Summary: | 碩士 === 國立臺北科技大學 === 分子科學與工程系有機高分子碩士班 === 106 === This thesis mainly studies the photovoltaic behaviors of two different types of new low bandgap conjugated polymers. We compare conjugated polymers of different structures which based on Benzothiadiazole or Benzoselenodiazole derive low bandgap polymers. In the first conjugated polymer, an electron-deficient unit benzothiadiazole (BTD) monomer is added to enhance the optical absorption capability of the conjugated polymer, and the electron donor unit is 3,3-difluoro-2,2-bithiophene-5,5-diyl)bis(trimethyl-stannane)(DFBT-bisSn) to enhance the planarity of the polymer chain and to introduce long carbon chains into the thiophene, while the purpose of introducing long carbon chains is to increase solubility. By introducing different carbon chain lengths, enough conjugated side chains are arranged and stacked, and the arrangement of polymer chains tends to be flat. Polymer abbreviated as PBDOD-TF and PBDOT-TF, respectively and the effect alkyl chain on the bulk-heterojunction morphology and photovoltaic performance were investigated. The hole mobility µh of PBDOD-TF ((2.72±0.1.21)x10-4) and PBDOT-TF ((2.24±0.38)x10-4) are in the same order of magnitude with slightly higher values when compared to PBDOT-TF. Through the transmission microscope, we can see that the surface morphology of the film blended with the conjugated polymer and the fullerene derivative has a considerable domain size, which causes the electron donor and the electron acceptor to be unable to effectively utilize each other interface to transfer electrons and holes. Polymer solar cells were fabricated by using [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) as the acceptor with the inverted device configuration of ITO/ ZnO/ Polymers:PC61BM/ V2O5/ Ag. The solar device based on T2F-PBDTBT-OD/PC60BM blend showed power conversion efficiency (PCE) of 2.63% with a Voc of 0.84 ±0.01V, and Jsc of 4.9±0.54 mA/cm2. In contrast, the T2F-PBDTBT-OT device exhibited a lower PCE of 1.39% and Jsc of 2.41±0.18 mA/cm2 with slightly higher Voc of 0.88 ±0.01V.
In the second part, we synthesized novel two-dimensional conjugated polymer PDTBSeVTT-2TF based on 3,3-difluoro-2,2-bithiophene (2TF) as donor unit and 4,7-di(thiophen-2-yl)benzo[c][1,2,5]selenodiazole (DTBSe) as acceptor unit bearing vinyl-terthiophene (VTT) conjugated side chains along with two 2-octyldodecyl chains and the effect of processing temperature on bulk-heterojunction morphology and photovoltaic performance were investigated. The copolymer PDTBSeVTT-2TF exhibited broad absorption from 300-800 nm and a narrow optical bandgap of 1.57 eV with a deep HOMO of -5.57 eV. Polymer solar cells (PSCs) was fabricated by using [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as acceptor and PDTBSeVTT-2TF as donor with an inverted device configuration of ITO/ ZnO/ PDTBSeVTT-2TF:PC71BM/ V2O5/ Ag. The PDTBSeVTT-2TF:PC71BM blend solution were processed at two different temperature 50 °C and 65 °C, respectively. The blend solution processed from the 65°C device exhibited enhanced PCE of 5.03% with a Jsc of 10.99 mA/cm-2 compared with the blend solution processed at 50 °C, which had a PCE of 4.63 % with a Jsc of 10.15 mA/cm-2. This enhancement of PCE is probably due to the increased thermal motion of polymer chains dissociates the PDTBSeVTT-2TF clusters into into single molecules and small aggregates that facilitate the miscibility between the polymer and PC71BM to form nano-scale domains, thus increases the D/A interface and photocurrent.
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