Dang Xuan Long

A simple structured and efficient triazine-based molecule as an interfacial layer for high performance organic electronics

Achieving the state-of-the-art performance of solution processable and flexible organic electronics requires efficient, stable, and cost-effective interfacial layers (ILs). Here, we report an alcohol soluble phosphine oxide functionalized 1,3,5-triazine derivative (PO-TAZ) as an IL, which remarkably tailors the work function of conductors including metals, transparent metal oxides and organic materials, making it an ideal candidate for an interfacial material in organic electronics. Consequently, PO-TAZ thin films enable the fabrication of organic and organic–inorganic (perovskite) solar cells with power conversion efficiencies of 10.04% and 16.41%, respectively, and n-channel organic field-effect transistors with an electron mobility of 8 cm2 V−1 s−1. Owing to the low-cost processing associated with PO-TAZ and the tremendous improvement in device performances as compared to the devices without PO-TAZ along with ambient stability, PO-TAZ is a good choice for efficient organic electronics in large area printing processes.

Significant roles of low-temperature post-metallization annealing in solution-processed oxide thin-film transistors

Inspired by the silicide technology in manufacturing silicon devices and the ongoing lack of knowledge on post-metallization annealing in realizing oxide devices, we investigated post-contact annealing for solution-processed InGaZnO transistors. Low-temperature annealing in air is found to significantly improve device uniformity, reproducibility, and subthreshold charge transport. However, this method is highly dependent on the employed contact metal. Detailed examination of devices using Al, Au, and Cu reveals that the physics of a metal/semiconductor interface is vital to its post-anneal response, which results in distinct device characteristics. Our results provide clues to better understand oxide transistors and to optimize their performance.

Universal diffusion-limited injection and the hook effect in organic thin-film transistors

The general form of interfacial contact resistance was derived for organic thin-film transistors (OTFTs) covering various injection mechanisms. Devices with a broad range of materials for contacts, semiconductors, and dielectrics were investigated and the charge injections in staggered OTFTs was found to universally follow the proposed form in the diffusion-limited case, which is signified by the mobility-dependent injection at the metal-semiconductor interfaces. Hence, real ohmic contact can hardly ever be achieved in OTFTs with low carrier concentrations and mobility, and the injection mechanisms include thermionic emission, diffusion, and surface recombination. The non-ohmic injection in OTFTs is manifested by the generally observed hook shape of the output conductance as a function of the drain field. The combined theoretical and experimental results show that interfacial contact resistance generally decreases with carrier mobility, and the injection current is probably determined by the surface recombination rate, which can be promoted by bulk-doping, contact modifications with charge injection layers and dopant layers, and dielectric engineering with high-k dielectric materials.

Well-defined alternative polymer semiconductor using large size regioregular building blocks as monomers: electrical and electrochemical properties

Regioregular polymer semiconductors have demonstrated a well-ordered micro-crystalline morphology in thin films due to better π-stacking orientation resulting in efficient charge transport. We propose an effective synthetic strategy to achieve well-defined regioregular alternative donor–acceptor (D–A) type conjugated polymers using large molecular weight regioregular monomers. Using this synthetic route, various conjugated moieties can be systematically introduced in a single polymer backbone, and we developed a regioregular alternative D–A polymer, coded rr-PBTTh, based on thiophene as electron donating and benzothiadiazole as electron withdrawing groups. This new polymer possesses a highly planar conjugated backbone due to regioregularity and S⋯O and S⋯F non-covalent intramolecular conformational locks. rr-PBTTh exhibits well-balanced ambipolar transport characteristics mainly due to the balanced D–A molecular structure, and shows promising electrochromic performance with coloration efficiency up to 321.7 cm2 C−1 and rapid response time below 0.5 s.