Synthesis and characterisation of hybrid nanocomposites using polyvinylcarbazole and metal selenides to demonstrate photovoltaic properties

Abstract

Due to a high global demand for energy, research groups have been focusing a lot of energy into finding alternative and cleaner energy sources. Solar power has all the attributes to be the energy of the future. Solar power is abundantly available and is a cleaner form of energy as compared to the market-leading fossil fuels.

In this thesis, we consider new materials that can be used in hybrid solar cells. These new materials combine the properties of inorganic nanomaterials and polymers. The nanomaterials possess unique properties that can be exploited and the polymers allow for the thin films to potentially be light weight and flexible.

Copper selenide was synthesized and characterized to produce particles with different sizes as a function of time. These size variations are shown to emit a spectrum of different colours. In addition the particles synthesized at various temperatures are reported. Temperature had an effect on the size of the particles with bigger sizes obtained as the temperature was increased. Also shown in the results is that Cu2Se nanocrystals were quite resistant to changes with the sizes marginally increasing with increasing time and temperature. A hybrid material using a conductive polymer polyvinylcarbazole (PVK) and copper selenide was synthesized and used as the active layer via a spin coating technique to fabricate a solar cell. Varying amounts (10% - 50%) of Cu2Se nanocrystals were used in the polymer nanocomposites. The 10% weight loading resulted in the highest efficiency of 0.74% whilst successive addition of the nanocrystals affected the polymeric structure of PVK thus resulting in solar cells with even lower efficiencies.

Niobium selenide was synthesized via the colloidal method using TOP/HDA combination for the first time. The effect of time on the particles synthesized using a 1:1 mole ratio of Nb:Se was negligible with particles showing similar properties. The XRD of the samples revealed that they were amorphous thus making it difficult to conclusively say that niobium selenide was synthesized successfully. The samples were then annealed however only small improvements were observed. The concentration of the selenium was then increased in order to form the more common NbSe2 and NbSe3. The XRD showed the formation of NbSe2 and NbSe3 for 1:2 and 1:3 Nb:Se ratios respectively. In addition, the particles resembled 2D nanostructures readily observed in layered materials such as NbSe2 and NbSe3. However, some impurities in the form of oxides were still observed. Hybrid solar cells prepared from the amorphous 1:1, 1:2 and 1:3 Nb:Se samples were fabricated. The NbSe3 composite had the best performing solar cell with the power conversion efficiency of 3.234% with the amorphous particles generating no current.