ABSTRACT
The selection of side chains is important in design of conjugated polymers. It not only affects their intrinsic physical properties, but also has an impact on thin film morphologies. Recent reports suggested that a face-on/edge-on bimodal orientation observed in polymer thin films may be responsible for a three-dimensional (3D) charge transport and leads to dramatically improved mobility in donor-acceptor based conjugated polymers. To achieve a bimodal orientation in thin films has been seldom explored from the aspect of molecular design. Here, we demonstrate a design strategy involving the use of asymmetric side chains that enables an isoindigo-based polymer to adopt a distinct bimodal orientation, confirmed by the grazing incidence X-ray diffraction. As a result, the polymer presents an average high mobility of 3.8 ± 0.7 cm2 V-1 s-1 with a maximum value of 5.1 cm2 V-1 s-1, in comparison with 0.47 and 0.51 cm2 V-1 s-1 obtained from the two reference polymers. This study exemplifies a new strategy to develop the next generation polymers through understanding the property-structure relationship.
ABSTRACT
Organic single-crystalline heterojunctions are composed of different single crystals interfaced together. The intrinsic highly ordered heterostructure in these multicomponent solids holds the capacity for multifunctions, as well as superior charge-transporting properties, promising high-performance electronic applications such as ambipolar transistors and solar cells. However, this kind of heterojunction is not easily available and the preparation methods need to be developed. Recent advances in the efficient strategies that have emerged in yielding high-quality single-crystalline heterojunctions are highlighted here. The advantages and limitations of each strategy are also discussed. The obtained single-crystalline heterojunctions have started to exhibit rich physical properties, including metallic conduction, photovoltaic effects, and so on. Further structural optimization of the heterojunctions to accommodate the electronic device configuration is necessary to significantly advance this research direction.
ABSTRACT
MoS2 is widely used in many fields including spin-valleytronics, logic transistors, light emitting devices, clean energy and biology. However, controllable synthesis of two-dimensional MoS2 sheets remains a great challenge. We report the formation of round-shaped monolayer MoS2 domains with a tunable size and the shape transformation from triangle to round. A qualitative interpretation of the formation mechanism is presented and the process can be controlled by either a thermodynamic or a kinetic growth regime depending on the growth rate. The round-shaped MoS2 domains show a high electron mobility of 1.39 cm(2) V(-1) s(-1), comparable to the mechanically exfoliated counterparts. Our study reveals the dominant factors that influence the synthesis of MoS2 and improves our understanding of the nucleation and growth mechanisms of MoS2, towards fine control over the synthesis of MoS2 and other TMDs.
ABSTRACT
Aligned ferroelectric single crystals of (3-pyrrolinium)(CdCl3 ) can be prepared from solution on top of aligned semiconducting C60 single crystals using an orthogonal solvent. Memory devices based on these ferroelectric/semiconductor bilayered heterojunctions exhibit much larger hysteresis compared with that of only C60 single crystals. More importantly, the introduction of the ferroelectric layer induces the memory window without dramatically reducing the charge mobility.
