Quantum Dot Sensitized Solar Cells Thesis

Quantum Dot Sensitized Solar Cells Thesis-56
experimental voltage-current curve based on the diode model.

experimental voltage-current curve based on the diode model.

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• To what extent does a ferrocyanide/ferricyanide electrolyte with optimised concentrations improve the overall QDSSC performance?

These questions were answered by: • Synthesising and characterising quantum dots (using Pb S as model) by using established and modified parameters.

• What are the optimal reduced and oxidised species concentrations in a ferrocyanide/ferricyanide electrolyte to maximise the performance of a Cd S QDSSC?

• Which parameters in the diode model of the Cd S QDSSC cell have the most influence on cell performance with this redox electrolyte and which among these parameters are sensitive to tolerance changes?

There is a plethora of renewable energy sources that wait for us to be harnessed - wind, geothermal, wave, solar energies, to name a few - which are more than enough to supply our energy demand.

Quantum Dot Sensitized Solar Cells Thesis

The sun, with its enormous amount of free energy at 3 x 10^24 Joules/year, is estimated to be capable of covering 10,000 times the world's energy requirement at the beginning of the 21st century.Vis-à-vis FRET, an enhanced solar cell performance and a PCE of 1.8% was obtained.Further, the hole transporting ability of the conventional Sn2-/S2- layer was also improved by use of poly(3,4-ethylenedioxythiophene) microfibers.• Designing an optimal reduced and oxidised species concentration combination and observe its effect on the cell's conversion efficiency. Pb S QD size engineering can be done by keeping the precursor ratio constant while the injection temperature variable. Pb S QDs can be stored in air/dark without effect on its optical properties after one bubbling in nitrogen. Pb S QDs remain optically stable after 60 days in air/dark environment. Pb S QDs can be dried when needed to be transported and re-dispersed without adverse effect on the absorption. 0.2 M reduced species concentration is the optimal reduced species concentration in this study. 0.01 M oxidised species concentration results in relatively slower charge recombination at the Ti O2 surface hence high FF results in longer lifetime thus higher open circuit voltage (VOC). At fixed oxidised species concentration (0.01 M) in the electrolyte, a sufficiently low (2 where the ideal value is 1) as the irradiation intensity was increased. The extracted parameters that were sensitive to slight changes (± 1%) were identified as the ideality factor, n, and shunt resistance, Rh. The extracted ideality factors result showed that the interfacial recombination increased once the irradiation is more than 100% i.e. Emission and excitation spectral measurements on QDs should also be conducted. Further studies on the QD ageing beyond 180 days in order to establish QD's practical lifetime. Further studies on this QDSSC model should be focused on other components such as the sensitiser, counter-electrode, and passivating agent since the maximum theoretical VOC has already been achieved in this study. Reasons why the ideality factor increases (moving away from ideal) as the irradiation intensity is increased need to be further investigated together with ways to improve the charge recombination kinetics. Since the maximum theoretical VOC is almost achieved in this thesis, it is recommended that the next study be focused on how to improve the short circuit current (JSC) and fill factor (FF).In summary, the optimised ferrocyanide/ferricyanide concentration ratio of the redox electrolyte in the QDSSC examined in this thesis has been found to be 0.2/0.01 M resulting in a VOC of 0.8 V, a FF of 0.66, and JSC of 3.8 m A/cm^2, corresponding to an IPCE of 57% at 410 nm and overall conversion efficiency of 2%.Apart from the use of carbon nanostructures, another concept, FRET, was also exploited in this work to realize improved efficiencies in QDSSCs.An electrode tethered QD assembly of Zn S/Cd S/Zn S was used as the donor and copper phthalocyanine (Cu Pc) molecules dissolved in the electrolyte were used as the acceptors.Plasmonic effects were tapped for improving solar cell responses, by integrating Au microfibers with Cd S/Ti O2 electrodes.This work was further extended by combining this plasmonic photoanode with an electrical double layer capacitor based on multiwalled carbon nanotubes (MWCNTs).The most common method of harvesting solar energy is through photovoltaic (PV) technology in which next-generation PV technologies are vastly becoming popular due to limitations in the mainstream solar PVs i.e. One of these next-generation PVs is the quantum dot sensitised solar cell (QDSSC), the focus in this thesis.Quantum dots (QD) which are semiconductor nanomaterials used as sensitiser in QDSSCs, are physically very small in size, usually below 10 nm.


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