Institute of Solid State Physics
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SS22 WS22 SS23 WS23 SS24 WS24 Guidelines for Master Students
Surface crystallization of Ph‐BTBT‐C10 Benzothieno[3,2-b][1]benzothiophene (BTBT) derivatives are very promising candidates in the field of solution processable organic semiconductors that could enable low-cost production of flexible and large-area electronics. BTBT derivatives have delivered some of the highest mobilities among organic semiconductors. Especially 2-decyl-7-phenyl-[1] benzothieno[3,2-b][1] benzothiophene (Ph-BTBT-10) drew attention after uniform and molecularly flat polycrystalline thin films were produced. In this work the surface crystallization behavior of Ph-BTBT-10 is investigated together with its phase transitions during heating up to 240°C and cooling back. Thin films starting from the monolayer regime up to thick films were prepared by spin coating. The films were investigated in terms of crystalline properties and thin film morphology by X-ray diffraction, X-ray reflectivity and Grazing Incidence X-ray diffraction, atomic force microscopy and optical microscopy. It is shown that at the lowest concentration of 0.3 g/l an uncompleted monolayer of standing molecules with the aromatic core pointing towards the substrate is formed. At higher concentrations between 0.5 g/l and 3 g/l strong island growth starts which leads to the formation of macroscopic islands at the highest concentration of 5 g/l. The phase transition behavior at elevated temperatures was observed trough in-situ X-ray reflectively measurements. The disappearance and shift of Bragg peaks during the transition into the crystal E phase and back to the bulk phase is demonstrated. Furthermore it is shown that at concentrations and spin speeds between 1.5 - 5 g/l and 1000 - 1600 rpm a disordered crystal E phase is formed under ambient conditions. This phase shows comparable Bragg peak positions as the crystal E phase above 149°C, however the peaks are much broader suggesting a disordered crystal E phase. |
