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Title: Advanced materials for organic solar cells : influence of generation and pH on PAMAM-based devices
Author: Alshahrani, Thamraa Mohammed
ISNI:       0000 0004 5914 5888
Awarding Body: Prifysgol Bangor University
Current Institution: Bangor University
Date of Award: 2016
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A systematic approach has been used to investigate the application of new PAMAM dendrimers materials as acceptors in the fabrication of different organic photovoltaic (OPV) structures. In the first part of this work, a new PAMAM cores (FC0, FC1 and FC2) as well as different PAMAM generations (G0, G0.5, G1 and G2) were used as acceptors in the fabrication of organic bulk heterojunction (OBHJ) structures. The devices exhibited electronic properties dependent on morphology and optical absorption as well as the surface group in the PAMAM generations. Power conversion efficiency (PCE) of 0.2%, under AM1.5G illumination (100 mW/cm2), was found for PAMAM-FC2 based OBHJ devices. Based on this result, different generations (G0, G0.5, G1 and G2) were synthesis from PAMAM FC2 core to improve the efficiency. Devices based on PAMAM G0.5 (half generation with ester terminated group in the surface group) with condense branching units and good connections in the composition active layer film resulted in a PCE of 1.8 %. For comparison, devices based on IC70BA were also investigated in OBHJ structures. The results show that devices, with the polymer to IC70BA ratio of 1:1 and annealed at 1500C for 10 min, exhibited the best device performance (JSC = 23. 33 mA/cm2, VOC = 0.53 V, FF 0.44, and PCE = 5.8 %). The second part of this work aimed to investigate the effect of generation and pH of the new acceptor PAMAM dendritic materials on the performance of organic bilayer heterojunction (OBiHJ) structures. Increasing PAMAM dendritic generation from G0.5 to G2.5 influences significantly the bilayer OHJ solar cells efficiency performance. PCE of 7 % were achieved at the natural PAMAM G2.5 pH 6.85. Atomic force microscopy shows that PAMAM morphology changes with their generation and pH values. The improved performance seen with PAMAM G2.5 at natural pH was due to the number of surface groups and tertiary amines in the dendrimer are increases with generation size and at different pH values. The protonation of dendrimers varies with the generation size. The PAMAM G0 copolymerised with a thienopyrrolodione (TPD) accepting moiety as A-A copolymer structures in order to enhance their charge transport properties was also investigated. PAMAMG0-TPD was used as electron acceptor component coupled with P3HT as donor in OHJ solar cell structures. The devices yield a PCE of about 4.5 %. This result demonstrated the potential to use PAMAM-TPD based conjugated copolymers as acceptor component for organic solar cells. The third part of this work is based on the moderate performance of part two. Three different organic tandem solar cells were fabricated and characterised. They have the same active layer (P3HT:IC70BA) as bulk-heterojunction structure in the bottom cells where the top cell is a bilayer heterojunction structure. The differences between the three structures is the acceptor layer of the top cells. From results in part two PAMAM-G1.5 (pH= 7.03), PAMAM-G2.5 (pH= 6.85) and PAMAM-G0-TPD were chosen as they have the highest efficiency to be applied in the top cells of organic tandem structures. The results from the three tandem structures displayed reasonably high PCE due to the enhanced VOC.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available