Self-Doping Naphthalene Diimide Conjugated Polymers for Flexible Unipolar n-Type OTFTs

The development of high-performance organic thin-film transistor (OTFT) materials is vital for flexible electronics. Numerous OTFTs are so far reported but obtaining high-performance and reliable OTFTs simultaneously for flexible electronics is still challenging. Herein, it is reported that self-doping in conjugated polymer enables high unipolar n-type charge mobility in flexible OTFTs, as well as good operational/ambient stability and bending resistance. New naphthalene diimide (NDI)-conjugated polymers PNDI2T-NM17 and PNDI2T-NM50 with different contents of self-doping groups on their side chains are designed and synthesized. The effects of self-doping on the electronic properties of resulting flexible OTFTs are investigated. The results reveal that the flexible OTFTs based on self-doped PNDI2T-NM17 exhibit unipolar n-type charge-carrier properties and good operational/ambient stability thanks to the appropriate doping level and intermolecular interactions. The charge mobility and on/off ratio are fourfold and four orders of magnitude higher than those of undoped model polymer, respectively. Overall, the proposed self-doping strategy is useful for rationally designing OTFT materials with high semiconducting performance and reliability.

Small-molecule ambipolar transistors

Ambipolar transistor properties have been observed in various small-molecule materials. Since a small energy gap is necessary, many types of molecular designs including extended π-skeletons as well as the incorporation of donor and acceptor units have been attempted. In addition to the energy levels, an inert passivation layer is important to observe ambipolar transistor properties. Ambipolar transport has been observed in extraordinary π-electron systems such as antiaromatic compounds, biradicals, radicals, metal complexes, and hydrogen-bonded materials. Several donor/acceptor cocrystals show ambipolar transport as well.

Tuning of energy levels, transport properties and device performance of naphthalenediimide derivatives by introduction of Michael addition reaction

NDI derivatives have been synthesized via Michael addition reaction with uplifted HOMO–LUMO energy levels and strong CT interaction in MA products generally not achieved by simple imide-N substitutions.

Positional Effect of the Triphenylamine Group on the Optical and Charge-Transfer Properties of Thiophene-Based Hole-Transporting Materials

Hybrid organic-inorganic perovskite solar cells (PSCs) have shown significant potential for use in the energy field. Typically, hole-transporting materials (HTMs) play an important role in affecting the power conversion efficiency (PCE) of PSCs. A deep understanding of the structure-property relationship plays a vital role in developing efficient HTMs. Herein, the relationship between the structure and properties of two small organic HTMs H2,5 and H3,4 were systematically investigated in terms of the electronic and optical properties, the hole-transporting behavior by using density functional theory (DFT) and Marcus electron transfer theory. The results demonstrated that the high power conversion efficiency of the H2,5-based PSC was caused by strong interactions with the perovskite material on the interface and an enhanced hole mobility in H2,5 compared with H3,4. The strong interaction derives from the short bond length of O atom of HTM and Pb atom of perovskite material, and the highly hole mobility derives from the quasi-planar conjugated conformation and tight packing model of neighboring molecules in H2,5. In addition, we found that the planar structure enhances the intermolecular interaction between HTM and perovskite materials compared with the 'V'-shaped molecule. Importantly, we also note that the HOMO level of the isolated molecule is not always proportional to the open-circuit voltages of PSCs since the HOMO level might move toward a higher level when the interaction between HTM and interface of perovskite was included. The work gives essential information for rational designing efficient HTMs.

Recent progress in the usage of tetrabromo-substituted naphthalenetetracarboxylic dianhydride as a building block to construct organic semiconductors and their applications

The recent synthetic strategies and significant applications of TBNDA and their derivatives as promising building blocks to construct π-expanded semiconductors have been carefully summarized in this review.

Linear-type carbazoledioxazine-based organic semiconductors: the effect of backbone planarity on the molecular orientation and charge transport properties

We report the synthesis of a linear-type dibromocarbazoledioxazine (CZ) derivative as a new precursor for semiconducting polymers. The chemical structures of the CZ unit and its polymers with thiophene or thienothiophene spacers (namely, PCZT and PCZTT) were fully characterized. PCZT and PCZTT possessed similar medium optical band gap (E^opt_g) and electrochemical band gap (E^cv_g) of around 1.70 eV estimated from the onset absorption and electrochemical redox potentials of the thin films, respectively. Computational density functional theory (DFT) calculations suggested that the backbone of the PCZT might be highly twisted, while that of PCZTT could be very planar. The effect of different backbone geometries on the charge–transport properties was studied by using thin film transistors (TFTs). The TFT device based on PCZTT showed a four times higher hole mobility as compared to that based on PCZT. The superior TFT performances of PCZTT were reasonably attributed to its edge-on backbone packing orientations toward the Si substrate revealed by the grazing-incidence wide-angle X-ray scattering (GIWAXS), which was favorable for in-plane charge transport in the TFT devices.

A linear-type dibromocarbazoledioxazine (CZ) derivative and its two polymers are newly designed and synthesized. Structure–property relationship studies reveal that PCZTT shows a four times higher hole mobility than PCZT.

One-step rapid synthesis of π-conjugated large oligomers via C–H activation coupling

A series of DPP-based π-conjugated oligomers with linear, V-shaped, star-shaped, and twisted or 3D geometries and MWs of 1500–3300 has been facilely obtained in one step via Pd-catalyzed DA coupling.