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Browsing Energy Storage by Author "Amollo, Tabitha A."
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Publication Germanium quantum dot/nitrogen-doped graphene nanocomposite for high-performance bulk heterojunction solar cells(Royal Society of Chemistry, 2018-06-30) Amollo, Tabitha A.; Mola, Genene T.; Nyamori, Vincent O.This study presents the successful synthesis of a novel nanocomposite, namely a germanium quantum dot/nitrogen-doped graphene nanocomposite (GeQD/NGr), and its use in the modification of the photoactive medium of bulk heterojunction solar cells (BHJ-SCs). The nanocomposite was prepared in two sequential steps. Firstly, a reduced graphene oxide-germanium oxide nanocomposite (rGO-GeO2) was synthesized by microwave-assisted solvothermal reaction. The second step involved simultaneous N-doping of graphene and reduction of GeO2 to obtain the GeQD/NGr nanocomposite by thermal treatment. The nanocomposite consists of highly crystalline, spherical shaped GeQDs with a mean diameter of 4.4 nm affixed on the basal planes of NGr sheets. Poly-3-hexylthiophene (P3HT), (6-6)phenyl-C60-butyric acid methyl ester (PCBM) and GeQD/NGr were used as the photoactive layer blend in the fabrication of BHJ-SCs. Enhanced short-circuit current density (Jsc) and fill factor (FF) is derived from the incorporation of the GeQD/NGr nanocomposite in the active layer. The nanocomposite in the active layer blend serves to ensure effective charge separation and transportation to the respective electrodes. Consequently, an improvement of up to 183% in the power conversion efficiency is achieved in the BHJ-SCs by the GeQD/NGr modification.Publication Improved short-circuit current density in bulk heterojunction solar cells with reduced graphene oxide-germanium dioxide nanocomposite in the photoactive layer(Elsevier, 2020-11) Amollo, Tabitha A.; Mola, Genene T.; Nyamori, Vincent O.In the quest to improve the optical absorption and electrical transport of poly-3-hexylthiophene (P3HT) and (6-6) phenyl-C61-butyric acid methyl ester (PCBM) blend film, reduced graphene oxide-germanium dioxide nanocomposite (rGO-GeO2) was employed in the photoactive layer of thin film organic solar cells. Bulk heterojunction solar cells (BHJ SCs) with rGO-GeO2 composite in the active layer exhibited an increase in power conversion efficiency (PCE) of up to 53%. Significant improvement in the measured photocurrent is achieved by the incorporation of rGO-GeO2 in the active layer. High short-circuit current density (Jsc) of up to 17 mA/cm2 is attained in the BHJ SCs. The high Jsc shows that the inlay of rGO-GeO2 in the active layer facilitates exciton separation and creates percolation pathways for charge transport to the electrodes. Charge separation is energetically favoured by a built-in potential difference between the donor and acceptor phases of the active layer. Hence, the incorporation of rGO-GeO2 composite in the active layer improves its charge photogeneration, separation and transport to yield high Jsc and enhanced PCE.Publication Organic solar cells: Materials and prospects of graphene for active and interfacial layers(Taylor & Francis group, 2019-06-26) Amollo, Tabitha A.; Mola, Genene T.; Nyamori, Vincent O.Photovoltaics is a portentous alternative to the nonrenewable energy resources. Organic solar cells (OSCs) offer several advantages over inorganic counterparts in terms of low-cost device production, simple solution-based processing, flexibility, light-weight and compatibility with roll-to-roll fabrication. This review comprehensively examines the latest research developments towards high-performance OSCs. Device processing conditions and engineering along with material developments for the active and interfacial layers are examined. Different device structures and their benefits and limitations are highlighted. The interfacial layer materials including the polymers and metal oxides together with their integration and performance in functional OSCs are examined. A salient aspect of this review is the design of donor and acceptor materials to address the optical and electronic properties requirement for optimized device efficacy of OSCs. In this regard, the prospects of tailoring the band gap of donor polymers alongside the adoption of non-fullerene acceptors with complementary optical absorption for improved solar energy harvesting is elucidated. Further, graphene’s feasibility as an active or interfacial layer material is reviewed. Hence, this article provides perspectives and strategies on further development of solution-processable donor, acceptor and interfacial materials for high efficiency devices, required in commercialization of OSCs.