Browsing by Author "Eninges Asmare"

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    Aggregation-Dictated Photophysics of Conjugated Polymers
    (Addis Ababa University, 2025-01-30) Eninges Asmare; Newayemedhin Aberra
    Improving the PCE in OPVs is among the pioneering researches to satisfy the world energy demand. Recently PCEs of above 19% are recorded by improving morphology of the active layer in OSCs. Molecular aggregation, which was _rst developed by Kasha, and Jelly and Schiebe, plays a role on the morphology of conjugated polymers. In this work, we study the aggregation photophysics of three copolymers dividing into two objectives. We used three methods - Franck- Condon (FC) analysis, HR factor evolution with temperature, and relative QY calculation - to determine the aggregates types in a benzodithiophene-isoindigo-based (PBDTI-DT) copolymer which show that both H- and J-aggregation types present, and the QY calculation clearly indicates dominance of H-aggregates. As a second work the e_ect of backbone conformation on the aggregation photophysics of isoindigo-based copolymers, namely, P2TI and P2TITT is studied. P2TI was systematically tuned by inserting TT into the former resulting in modi_cation of the backbone and was found to a_ect the planarity due to reduced steric hindrance between the donor and the acceptor units, which was evidenced from the di_erence in oscillator strength of the _rst excited state transition. Temperature-dependent PL of the two polymers was well reproduced using two FC progressions, indicating the formation of both H- and J-type aggregates. This was supported by the presence of two emission lifetimes obtained from time-resolved uorescence measurements. The evolution of the _rst two vibronic peaks with temperature clearly showed stronger interchain interaction in P2TITT.