Nitroacetylacetone as a Cofuel for the Combustion Synthesis of High-Performance Indium–Gallium–Zinc Oxide Transistors

Thin-film combustion synthesis has been utilized for the fabrication of solution processed high-performance metal-oxide thin-film transistors (MOTFTs) at lower temperatures than conventional sol–gel processes. The fuel-oxidizer ensemble in the MO precursor solution/film plays an important role in achieving high-efficiency and low-residual combustion byproducts. However, unlike conventional bulk combustion, only a very limited number of thin-film fuels have been investigated. Here we report the use of an efficient new cofuel, 3-nitroacetylacetone (NAcAcH), incorporating a −NO₂ group, for the combustion synthesis of display-relevant indium–gallium–zinc-oxide (IGZO) thin films. Compared to the traditional acetylacetone (AcAcH) fuel, a higher enthalpy of combustion (988.6 vs 784.4 J/g) and a lower ignition temperature (107.8 vs 166.5 °C) are achieved for NAcAcH-based formulations. The resulting NAcAcH-derived IGZO TFTs exhibit far higher average electron mobilities (5.7 cm² V^–1 s^–1) than AcAcH-derived TFTs (2.7 cm² V^–1 s^–1). More importantly, when combining AcAcH with NAcAcH as cofuels in an optimal molar ratio of 1.5:0.5, an even larger TFT electron mobility (7.5 cm² V^–1 s^–1) and more stable devices are achieved. Comprehensive IGZO precursor/film analysis and characterization by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), grazing incidence X-ray diffraction (GIXRD), and X-ray reflectivity (XRR) explain the basis of the film microstructure and TFT performance trends

Bithiophenesulfonamide Building Block for π‑Conjugated Donor–Acceptor Semiconductors

We report here π-conjugated small molecules and polymers based on the new π-acceptor building block, bithiophenesulfonamide (BTSA). Molecular orbital computations and optical, electrochemical, and crystal structure analyses illuminate the architecture and electronic structure of the BTSA unit versus other acceptor building blocks. Field-effect transistors and photovoltaic cells demonstrate that BTSA is a promising unit for the construction of π-conjugated semiconducting materials

Enhanced Light Absorption in Fluorinated Ternary Small-Molecule Photovoltaics

Using small-molecule donor (SMD) semiconductors in organic photovoltaics (OPVs) has historically afforded lower power conversion efficiencies (PCEs) than their polymeric counterparts. The PCE difference is attributed to shorter conjugated backbones, resulting in reduced intermolecular interactions. Here, a new pair of SMDs is synthesized based on the diketopyrrolopyrrole–benzodithiophene–diketopyrrolopyrrole (BDT-DPP₂) skeleton but having fluorinated and fluorine-free aromatic side-chain substituents. Ternary OPVs having varied ratios of the two SMDs with PC₆₁BM as the acceptor exhibit tunable open-circuit voltages (<i>V</i>_ocs) between 0.833 and 0.944 V due to a fluorination-induced shift in energy levels and the electronic “alloy” formed from the miscibility of the two SMDs. A 15% increase in PCE is observed at the optimal ternary SMD ratio, with the short-circuit current density (<i>J</i>_sc) significantly increased to 9.18 mA/cm². The origin of <i>J</i>_sc enhancement is analyzed via charge generation, transport, and diffuse reflectance measurements, and is attributed to increased optical absorption arising from a maximum in film crystallinity at this SMD ratio, observed by grazing incidence wide-angle X-ray scattering

Enhanced Fill Factor through Chalcogen Side-Chain Manipulation in Small-Molecule Photovoltaics

The fill factor (FF) of organic photovoltaic (OPV) devices has proven difficult to optimize by synthetic modification of the active layer materials. In this contribution, a series of small-molecule donors (SMDs) incorporating chalcogen atoms of increasing atomic number (<i>Z</i>), namely oxygen, sulfur, and selenium, into the side chains are synthesized and the relationship between the chalcogen <i>Z</i> and the FF of OPV devices is characterized. Larger <i>Z</i> chalcogen atoms are found to consistently enhance FF in bulk-heterojunction OPVs containing PC₆₁BM as the acceptor material. A significant ∼8% FF increase is obtained on moving from O to S to Se across three series of SMDs. The FF enhancement is found to result from the combination of more ordered morphology and decreased charge recombination in blend films for the high-<i>Z</i>-chalcogen SMDs. Because this FF enhancement is found within three series of SMDs, the overall strategy is promising for new SMD materials design