Aggregate Structures & Opto-electronic Properties Of Violanthrone Derivatives

The development of organic electronics advances the applications of organic semiconductors in the organic light-emitting diodes (OLEDs), organic field effect transistors (OFETs), and organic solar cells (OSCs). To obtain high-efficiency OSCs, not only the proper band structure with the narrow band gap, but also the excellent charge transport performance are required for the optical active layer. To meet these two demands, it is necessary that organic molecules should have large successiveπsystem as well as strong actions between molecules so that electrons can move easily within and between molecules. Accordingly, in this dissertation, four kinds of violanthrone derivatives with different substituents,3,4,5, and 6, were synthesized. Through thermal analysis, UV-Vis absorption and cyclic voltammetry, the effect of different substituents on optical properties and energy levels was investigated. It was found that four compounds can be potentially in applied in OSCs because of their narrow band gap, proper HOMO and LUMO levels, and strong intermolecular actions. Furthermore, by concentration-depend NMR spectroscopy and DFT calculations, the conformation of 3 dimer was disclosed:there exist stronger intermolecularπ-πactions. Finally, bulk heterojunction (BHJ) OSCs based on four violanthrone derivatives as active layer were fabricated to investigate the relationship between band structure, molecules aggregation, film morphology and performance of photovoltaic devices. Among 4 compounds, solar cells based on 5 achieved a conversion efficiency of 0.54% without optimization. This good performance depended on highly homogenous morphology of the active film and good charge transport properties in relative successive phase. The above results would provide us useful information and tools in the improvement of opto-electronic properties of organic semicondutors through the tuning of their molecular and aggregate structures.