Polymeric-bimetallic oxide nanoalloy for the construction of photovoltaic cells
Research in renewable energy has become a focal point as a solution to the energy crisis. One of renewable forms of energy is solar energy, with the main challenge in the development of the solar cells being the high cost. This has led to the exploration of the use of organic molecules to construct solar cells since it will lead to lowered costs of construction. The focus of this research is on the synthesis and characterisation of the polyaniline derivatives materials and zinc gallate for application in the construction of hybrid solar cells with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as an acceptor. The polyaniline (PANi) and doped polyaniline derivatives, polyaniline phenathrene sulfonic acid (PANi-PSA), poly[ortho-methyl aniline] phenanthrene sulfonc acid (POMA-PSA) poly[ortho-methyl aniline] anthracene sulfonc acid (POMA-ASA) were produced via chemical synthetic procedures. The zinc gallate (ZnGa2O4) was also produced using a chemical method. The vibrational and electronic spectra of the polymers and zinc gallate were interrogated independently and dependently. Electronic transitions due to charge defects (polarons and bipolarons) were observed for the polymers that are doped. The PANi was the one with the lowest band gap of 2.4 eV with the POMA-ASA having the widest bandgap of 3.0 eV. The XRD and TEM analysis of the polymers revealed characteristics that show that the PANi has the highest level of crystallinity and the POMA-ASA displayed the least level of crystallinity. The electronic data, XRD, TEM data led to the conclusion that the conductivity of the polymers is decreasing in the following sequence, PANi > PANi-PSA > POMA-PSA > POMA-ASA. The photoluminescence of the polymers alone and with the nanoparticles was investigated in solution and on an ITO coated glass substrate. Photoluminescence was observed for the polymers due to relaxation of the exciton and also from the formation of excimers. The relaxation due to the exciton was observed at higher energy levels, while the one that is as a result of the excimer formation was seen at lower energy levels. Enhancement of the peak due to the excimer was observed when the compound is mixed with the nanoparticles in solution. When the analysis was done on the ITO coated glass substrate, it was found that zinc gallate does not lead to quenching of the emission of the polymers; hence it can not be used as an acceptor in this particular system. The electrochemical behaviour of the polyaniline derivatives was investigated using cyclic voltammetry and electrochemical impedance spectroscopy. Interaction of the polymers with the PCBM (acceptor) was investigated using UV-visible absorption spectroscopy and photoluminescence spectroscopy. It was able to quench the photoluminescence of the polymers. Hence it was used as an acceptor in the construction of the photovoltaic cells. The polymers alone and with the nanoparticles were used in the formation of bulk heterojunction photovoltaic cells with PCBM as an acceptor. The photovoltaic behaviour was investigated and PANi was the one that displayed the highest efficiency.