Enhancement of Photoconversion Efficiency of P3HT:PCBM Polymer Solar Cell Using Squarylium iii Dye

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Tembo, Moses
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University of Zambia
Ternary systems comprising of poly(3-hexylthiophene)(P3HT):(6,6)-phenyl-C61 butyric acid methyl ester (PCBM) and varying amounts of squarylium dye III (SQ3) were prepared and deposited by spin coating to obtain nano-size thin films. The films produced were subsequently annealed at 140 C for 10 min. Absorption spectra and electrical measurements were used to evaluate the effects of thermal annealing and dye loading on the different blends. The films were characterized for their surface morphology and film thickness using atomic force microscopy. Photo-conversion efficiencies were determined following current density – voltage (J-V) measurements under dark and illumination conditions enabling determination of various solar cell parameters. A significant increase in the maximum peak absorbance, from 0.30 to 0.35 a.u. was observed by incorporating SQ3 molecules at 13 % w/w loading. The absorption range was also observed to broaden (400 – 700 nm) extending to the near infra-red. The inclusion of SQ3 molecules resulted in enhanced light harvesting capacity due to widening of the absorption range. This consequentially resulted in an increase in photogenerated excitons and short circuit current (Isc). The HOMO of SQ3 is reported to be located between the HOMO and LUMO of levels of P3HT and PCBM. It has been further suggested that incorporation of SQ3 molecules introduce a second exciton generation system and charge transfer mechanism. Photoinduced charge transfer is not only favourable between P3HT and PCBM but also between SQ3 and PCBM. Thus, the synergistic effect of improved light harvesting characteristics with additional exciton generation and charge transfer mechanism resulted in an increase in photoconversion efficiency (η). The open circuit voltage (Voc), Isc, fill factor (FF) and η in the control P3HT:PCBM were 0.53 V, 5.78 mA, 0.35 and 1.3 % which change to 0.64 V, 9.68 mA, 0.40 and 3.9 % in P3HT:SQ3:PCBM blends. Thus the inclusion of SQ3 into the P3HT:PCBM polymer blends resulted in a threefold increase in photoconversion efficiency.
Master of Science in Physics.
Photovoltaic cells , Photovoltaic power generation