Influence of chemical interactions on the electronic properties of BiOI/organic semiconductor heterojunctions for application in solution-processed electronics.

Bismuth oxide iodide (BiOI) has been viewed as a suitable environmentally-friendly alternative to lead-halide perovskites for low-cost (opto-)electronic applications such as photodetectors, phototransistors and sensors. To enable its incorporation in these devices in a convenient, scalable, and economical way, BiOI thin films were investigated as part of heterojunctions with various p-type organic semiconductors (OSCs) and tested in a field-effect transistor (FET) configuration. The hybrid heterojunctions, which combine the respective functionalities of BiOI and the OSCs were processed from solution under ambient atmosphere. The characteristics of each of these hybrid systems were correlated with the physical and chemical properties of the respective materials using a concept based on heteropolar chemical interactions at the interface. Systems suitable for application in lateral transport devices were identified and it was demonstrated how materials in the hybrids interact to provide improved and synergistic properties. These indentified heterojunction FETs are a first instance of successful incorporation of solution-processed BiOI thin films in a three-terminal device. They show a significant threshold voltage shift and retained carrier mobility compared to pristine OSC devices and open up possibilities for future optoelectronic applications.

Tailoring the Morphology of a Diketopyrrolopyrrole-based Polymer as Films or Wires for High-Performance OFETs using Solution Shearing.

Conjugated polymers often show efficient charge carrier transport along their backbone which is a primary factor in the electrical behavior of Organic Field Effect Transistor (OFETs) devices fabricated from these materials. Herein, a solution shearing procedure is reported to fabricate micro/nano wires from a diketopyrrolopyrrole (DPP)-based polymer. Millimeter to nanometer long polymer wires orientated in the coating direction are developed after a thorough analysis of the deposition conditions. It shows several morphological regimes-film, transition, and wires and experimentally derive a phase diagram for the parameters coating speed and surface energy of the substrate. The as-fabricated wires are isolated, which is confirmed by optical, atomic force, and scanning electron microscopy. Beside the macroscopic alignment of wires, cross-polarized optical microscopy images show strong birefringence suggesting a high degree of molecular orientation. This is further substantiated by polarized UV-Vis-NIR spectroscopy, selected area electron diffraction transmission electron microscopy, and grazing-incidence wide-angle X-ray scattering. Finally, an enhanced electrical performance of single wire OFETs is observed with a 15-fold increase in effective charge carrier mobility to 1.57 cm2 V-1 s-1 over devices using films (0.1 cm2 V-1 s-1 ) with similar values for on/off current ratio and threshold voltage.