Photovoltaic activity in benzobisoxazole based conjugated polymers
Reida, Molly (2010) Photovoltaic activity in benzobisoxazole based conjugated polymers. Masters thesis, Iowa State University.
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The material and photovoltaic properties of a new class of conjugated polymers was investigated. These two new polymers; poly (3,4-didodecylthiopene vinylene)-2,6-diyl benzo [1,2-d; 5,4-d’] bisoxazole] (cis-DD-PTVBBO) and poly (3,4-didodecylthiopene vinylene)-2,6-diyl benzo [1,2-d; 4,5-d’] bisoxazole] (trans-DD-PTVBBO) were synthesized by Malika Jeffries-El group (Department of Chemistry, Iowa State University). Electron affinities were measured be 3.02eV for cis-DD-PTVBBO and 3.10eV for trans-DD-PTVBBO. The optical bandgaps are around 2eV for both polymers. The low band gap and high electron affinity of these polymers suggest that they would be suitable candidates for use in bulk heterojunction solar cells with Phyenyl-C61-butyric acid methyl ester (PCBM). Solar cells using the cis-DD-PTVBBO and the trans-DD-PTVBBO as the electron donor were fabricated and device characteristics were measured. In addition, hole mobilities were measured and atomic force microscopy (AFM) characterization was performed to evaluate phase separation in the thin films of the active layers. Photovoltaic performance was lower than expected and is suspected to be due to poor solubility and large aggregates within the active layer thin film. In addition, it is suspected that poor performance may be due to internal charge transfer between the electron donating thiophene unit and electron accepting benzobisoxazole unit. Having these two units is good in the sense that it delocalizes the charge and reduces the band gap of conjugated polymers; however, it may also lead to reduced electron transfer to the PCBM phase, leading to poor performance of photovoltaic cells.
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