| Abstract [eng] |
This work investigates charge carrier transport and recombination processes in organic blend layers composed of the small-molecule semiconductor trans-stilbene and polymer materials – PVB and PEPC. Although single-crystal organic semiconductors exhibit exceptionally high carrier mobility, their application is limited by complex crystal growth and integration, which is why solution-processing methods are widely used, enabling the formation of crystalline layers with controlled morphology. In such systems, polymers improve film formation and help maintain favorable transport properties. Phase separation in stilbene/polymer blends was controlled to form morphologies that promote charge transport through stilbene crystallites. Two types of layers were fabricated using either PVB or PEPC (stilbene-to-polymer ratio 4:1), and both exhibited high crystallinity. In the PVB case, large crystalline regions formed without clear boundaries, whereas in the PEPC system individual crystallites of approximately 600 × 300 µm were observed. X-ray diffraction (XRD) showed that in both systems the dominant stilbene diffraction peaks belong to the same crystallographic family and are parallel throughout the layer, indicating an ordered orientation. Time-of-flight (TOF) measurements of PEPC/stilbene layers revealed mobilities in the range of 10^(−3)–10^(−2) cm²V^(−1)s^(−1), with electrons slightly more mobile than holes; however, this difference disappears at higher electric fields. Compared to single-crystal stilbene, hole mobility is reduced by about three orders of magnitude and electron mobility by about two, indicating the influence of structural and energetic disorder, although the values remain high for organic electronics. In PVB/stilbene layers, photo-CELIV measurements showed similar electron and hole mobilities of around 10^(−2) cm²V^(−1)s^(−1), reduced by roughly two orders of magnitude for holes and one for electrons, yet still efficient. Recombination studies revealed a trap-assisted mechanism and significantly extended carrier lifetimes reaching tens of microseconds, compared to less than 1 µs in single-crystal stilbene. This demonstrates that morphology control can effectively suppress recombination. In summary, introducing stilbene into PVB and PEPC matrices induces additional disorder, which only partially reduces the very high mobility while preserving favorable transport properties. At the same time, the observed recombination suppression in the PVB system through longer carrier lifetimes highlights the potential of morphology engineering for organic electronics. |
