Functional graphene: synthesis, characterization and application in optoelectronics

Hochschulschrift

Zusammenfassung: Graphene has recently attracted enormous attention within the scientific community due to its outstanding optical, electrical and mechanical properties, and is highly promising for various applications. Also, semiconducting CdSe quantum dots (QDs), with easily tunable optical and electrical properties, have already demonstrated their potential for application in various applications such as photovoltaics. In this thesis, the transparency, high carrier mobility and high specific surface area of graphene were combined with the optical properties of CdSe QDs in a novel hybrid material, CdSe QD decorated graphene. Based on the synergetic properties, the hybrid material has been successfully characterized by various methods and was introduced in the active layer of hybrid solar cells, remarkably enhancing the power conversion efficiency of the solar cells. Graphene oxide (GO) was synthesized by a modified Hummers method. Then, oxygen-containing groups within GO were reduced and partially transformed into thiol- functionalities. As a result, thiol-functionalized reduced graphene oxide (TrGO) was obtained. This was achieved by refluxing GO with phosphorus pentasulfide in dimethylformamide solvent. The thiol groups serve as anchor points for the attachment of nanoparticles. This was realized with CdSe QDs and ZnO nanoparticles, respectively via a self-assembly process, whereby novel hybrid materials were obtained: nanoparticle decorated TrGO. Various techniques and methods such as SEM, TEM, XPS, FTIR, UV-Vis absorption spectroscopy were used to characterize GO, rGO, TrGO and QD-TrGO hybrid materials. Based on the results, the materials were further modified and developed to obtain the desired properties and functionalities. Graphenes with different functionalities and reduction degrees were also investigated in comparison with carbon nanotubes using electron paramagnetic resonance (EPR) spectroscopy. For application in photovoltaics, CdSe QD-TrGO hybrid material was mixed with semiconducting polymers to form photoactive thin films which were utilized in hybrid solar cells. The photovoltaic cells showed significantly enhanced solar power conversion efficiencies. The graphene-based hybrid solar cells achieved a PCE of up to 4.24%, which is 46% higher than graphene-free cells and is in the range of the best efficiencies of hybrid quantum dot-polymer solar cells so far. Additionally, CdSe QD decorated rGO was tested regarding its utilization in photoconductors. Preliminary results proved that photo-induced charge transfer from QDs to graphene occurs, resulting in a measurable photocurrent contribution. This finding is consistent with those obtained from PL quenching experiments and the quenching of EPR signals for CdSe QD-TrGO hybrid materials. This finding further demonstrates the high potential of nanoparticle-graphene hybrid materials for optoelectronic applications

Angaben zum Objekt

• Standort: Deutsche Nationalbibliothek Frankfurt am Main
• Umfang: Online-Ressource
• Sprache: Englisch
• Anmerkungen: Albert-Ludwigs-Universität Freiburg, Dissertation, 2015

Klassifikation und Themen

• Klassifikation: Chemie

Beteiligte, Orts- und Zeitangaben

• Ereignis: Veröffentlichung
• (wo): Freiburg
• (wer): Universität
• (wann): 2015
• Urheber: Pham, Van Chuyen
• Beteiligte Personen und Organisationen: Krüger, Michael

Weitere Informationen

• DOI: 10.6094/UNIFR/10105
• URN: urn:nbn:de:bsz:25-freidok-101059
• Rechteinformation: Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Letzte Aktualisierung: 25.03.2025, 13:55 MEZ