Improving both performance and stability of n-type organic semiconductors by vitamin C.

Organic semiconductors (OSCs) are one of the most promising candidates for flexible, wearable and large-area electronics. However, the development of n-type OSCs has been severely held back due to the poor stability of their most candidates, that is, the intrinsically high reactivity of negatively charged polarons to oxygen and water. Here we demonstrate a general strategy based on vitamin C to stabilize n-type OSCs, remarkably improving the performance and stability of their device, for example, organic field-effect transistors. Vitamin C scavenges reactive oxygen species and inhibits their generation by sacrificial oxidation and non-sacrificial triplet quenching in a cascade process, which not only lastingly prevents molecular structure from oxidation damage but also passivates the latent electron traps to stabilize electron transport. This study presents a way to overcome the long-standing stability problem of n-type OSCs and devices.

Unraveling the crucial role of trace oxygen in organic semiconductors.

Optoelectronic properties of semiconductors are significantly modified by impurities at trace level. Oxygen, a prevalent impurity in organic semiconductors (OSCs), has long been considered charge-carrier traps, leading to mobility degradation and stability problems. However, this understanding relies on the conventional deoxygenation methods, by which oxygen residues in OSCs are inevitable. It implies that the current understanding is questionable. Here, we develop a non-destructive deoxygenation method (i.e., de-doping) for OSCs by a soft plasma treatment, and thus reveal that trace oxygen significantly pre-empties the donor-like traps in OSCs, which is the origin of p-type characteristics exhibited by the majority of these materials. This insight is completely opposite to the previously reported carrier trapping and can clarify some previously unexplained organic electronics phenomena. Furthermore, the de-doping results in the disappearance of p-type behaviors and significant increase of n-type properties, while re-doping (under light irradiation in O2) can controllably reverse the process. Benefiting from this, the key electronic characteristics (e.g., polarity, conductivity, threshold voltage, and mobility) can be precisely modulated in a nondestructive way, expanding the explorable property space for all known OSC materials.

Suppressing the Intrinsic Photoelectric Response of Organic Semiconductors for Highly-Photostable Organic Transistors.

Suppressing the photoelectric response of organic semiconductors (OSs) is of great significance for improving the operational stability of organic field-effect transistors (OFETs) in light environments, but it is quite challenging because of the great difficulty in precisely modulating exciton dynamics. In this work, photostable OFETs are demonstrated by designing the micro-structure of OSs and introducing an electrical double layer at the OS/polyelectrolyte dielectric interface, in which multiple exciton dynamic processes can be modulated. The generation and dissociation of excitons are depressed due to the small light-absorption area of the microstripe structure and the excellent crystallinity of OSs. At the same time, a highly efficient exciton quenching process is activated by the electrical double layer at the OS/polyelectrolyte dielectric interface. As a result, the OFETs show outstanding tolerance to the light irradiation of up to 306 mW·cm-2 , which far surpasses the solar irradiance value in the atmosphere (≈138 mW·cm-2 ) and achieves the highest photostability ever reported in the literature. The findings promise a general and practicable strategy for the realization of photostable OFETs and organic circuits.

Strain-Balanced Organic Semiconductor Film for Improving the Stability of Organic Field-Effect Transistors.

Strain-induced aggregate state instability in organic semiconductor (OSC) films is a critical and bottleneck issue in the practicalization process of organic field-effect transistors (OFETs), but this issue lacks deep insight and effective solutions for a long time. Herein, we developed a novel and general strain balance strategy for stabilizing the aggregate state of OSC films and enhancing the robustness of OFETs. The charge transport zone in OSC films located at the OSC/dielectric interface always suffers from the intrinsic tensile strain induced by substrates and tends to dewet. By introducing a compressive strain layer, the tensile strain can be well balanced and OSC films attain a highly stable aggregate state. Consequently, the OFETs based on strain-balanced OSC heterojunction films exhibit excellent operational and storage stability. This work provides an effective and general strategy to stabilize OSC films and gives guidance in constructing highly stable organic heterojunction devices.

Directly Patterning Conductive Polymer Electrodes on Organic Semiconductor via In Situ Polymerization in Microchannels for High-Performance Organic Transistors.

Conductive polymers are considered promising electrode materials for organic transistors, but the reported devices with conductive polymer electrodes generally suffer from considerable contact resistance. Currently, it is still highly challenging to pattern conductive polymer electrodes on organic semiconductor surfaces with good structure and interface quality. Herein, we develop an in situ polymerization strategy to directly pattern the top-contacted polypyrrole (PPy) electrodes on hydrophobic surfaces of organic semiconductors by microchannel templates, which is also applicable on diverse hydrophobic and hydrophilic surfaces. Remarkably, a width-normalized contact resistance as low as 1.01 kΩ·cm is achieved in the PPy-contacted transistors. Both p-type and n-type organic field-effect transistors (OFETs) exhibit ideal electrical characteristics, including almost hysteresis-free, low threshold voltage, and good stability under long-term test. The facile patterning method and high device performance indicate that the in situ polymerization strategy in confined microchannels has application prospects in all-organic, transparent, and flexible electronics.