SYNTHESIS, CHARACTERIZATIONS, AND APPLICATIONS OF CONJUGATED SMALL MOLECULES AND POLYMERS FOR ORGANIC SOLAR CELLS AND ORGANIC LIGHT-EMITTING DIODES

Date

2025-4-18

Author

Karakurt, Oğuzhan

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This thesis presents the design, synthesis, and characterization of advanced organic optoelectronic materials for organic solar cells (OSCs) and organic light-emitting diodes (OLEDs), with a focus on donor-acceptor (D-A) conjugated polymers, thermally activated delayed fluorescence (TADF) emitters, and gold nanoparticle (AuNP)-based nanostructures. Ligand-free AuNPs were incorporated into OSC active layers and stabilized via covalent interactions with thiol-functionalized benzoxadiazole-based conjugated polymers. The inclusion of AuNPs improved light absorption and reduced charge recombination, resulting in a 21.4% enhancement in power conversion efficiency (PCE), from 2.71% to 3.29%. Conjugated random copolymers incorporating benzoxadiazole-thienopyrrole acceptors and selenophene π-bridges exhibited tuneable bandgaps (1.67–1.70 eV). These polymers achieved a maximum PCE of 6.26%, with a short-circuit current density (JSC) of 11.44 mA/cm², an open-circuit voltage (VOC) of 0.80 V, and a fill factor (FF) of 68.81%. Further, silicon incorporation into D-A polymers with selenophene π-bridges was investigated. The resulting silicon-containing polymer exhibited improved π-conjugation, enhanced molecular planarity, and a reduced HOMO-LUMO bandgap (1.56 eV compared to 1.64 eV for the non-silicon-containing polymer). Silicon-containing OSCs demonstrated a PCE of 3.64%, with a JSC of 8.60 mA/cm², a VOC of 0.66 V, and an FF of 64.04%. TADF emitters featuring sulphur- and selenium-substituted triarylboron cores were developed for OLED applications. These emitters exhibited singlet-triplet energy gaps as low as 0.007 eV, photoluminescence quantum yields up to 85%, and external quantum efficiencies (EQE) of up to 25.3%. The selection of donor units and conformational control were shown to critically influence TADF efficiency.

Subject Keywords

Organic Solar Cells, Organic Light-Emitting Diodes, Donor-Acceptor Conjugated Polymers, Conjugated Small Molecules, Thermally Activated Delayed Fluorescence

URI

https://hdl.handle.net/11511/114481

Collections

Graduate School of Natural and Applied Sciences, Thesis