Renewable Energy Alternatives
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Browsing Renewable Energy Alternatives by Subject "University of KwaZulu-Natal"
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Publication Graphene for Thermoelectric Applications: Prospects and Challenges(Critical Reviews in Solid State and Materials Sciences, 2017-04-10) A, Amollo; Mola, Genene Tessema; Nyamori, VincentThermoelectric power generators require high-efficiency thermoelectric materials to transform waste heat into usable electrical energy. An efficient thermoelectric material should have high Seebeck coefficient and excellent electrical conductivity as well as low thermal conductivity. Graphene, the first truly 2D nanomaterial, exhibits unique properties which suit it for use in thermoelectric power generators, but its application in thermoelectrics is limited by the high thermal conductivity and low Seebeck coefficient resulting from its gapless spectrum. However, with the possibility of modification of graphene's band structure to enhance Seebeck coefficient and the reduction of its thermal conductivity, it is an exciting prospect for application in thermoelectric power generation. This article examines the electronic, optical, thermal, and thermoelectric properties of graphene systems. The factors that contribute to these material properties in graphene systems like charge carriers scattering mechanisms are discussed. A salient aspect of this article is a synergistic perspective on the reduction of thermal conductivity and improvement of Seebeck coefficient of graphene for a higher thermoelectric energy conversion efficiency. In this regard, the effect of graphene nanostructuring and doping, forming of structural defects, as well as graphene integration into a polymer matrix on its thermal conductivity and Seebeck coefficient is elucidated.Publication High-performance organic solar cells utilizing graphene oxide in the active and hole transport layers(Elsevier Ltd, 2018-06-22) Amollo, Tabitha A.; Mola, Genene T.; Nyamori, Vincent O.We have successfully synthesized and employed graphene oxide (GO) to boost photons harvesting and charge transport process in thin film organic solar cells (TFOSCs). The graphene oxide was inlayed in both the P3HT:PCBM-based photoactive medium of the device, as well as, a dopant in PEDOT:PSS hole transport buffer layer (HTL). The parameters of the solar cells produced with the inclusion of GO in the HTL and the active layer results in high short-circuit current densities (Jsc), which translated into high power conversion efficiencies (PCEs). GO in the HTL facilitates charge transport, selective electron blocking and hole injection at the interface for enhanced device performance. On the other hand, the use of GO in the active layer remarkably improves the optical absorption leading to high charge carriers photogeneration requisite to efficient OSCs. Similarly, effective exciton dissociation is energetically favoured in the GO modified active layer devices which corroborated with improved conductivity of the medium that assisted charge carriers transport processes. Enhanced photocurrent has been recorded, as high as 18 mA cm−2, from the TFOSCs by the inlay of GO in the active layer. Consequently, increased PCE of up to 40% and 120% is achieved by the inclusion of GO in the HTL and photoactive layers, respectively.