Very low bias stress in n-type organic single crystal transistors

Bias stress effects in n-channel organic field-effect transistors (OFETs) are investigated using PDIF-CN2 single-crystal devices with Cytop gate dielectric, both under vacuum and in ambient. We find that the amount of bias stress is very small as compared to all (p-channel) OFETs reported in the literature. Stressing the PDIF-CN2 devices by applying 80 V to the gate for up to a week results in a decrease of the source drain current of only ~1% under vacuum and ~10% in air. This remarkable stability of the devices leads to characteristic time constants, extracted by fitting the data with a stretched exponential - that are \tau ~ 2\cdot10^9 s in air and \tau ~ 5\cdot10^9 s in vacuum - approximately two orders of magnitude larger than the best values reported previously for p-channel OFETs.Comment: Submitted to Applied Physics Letters; 14 pages, 3 figure

Perylene-diimide molecules with cyano functionalization for electron-transporting transistors

Core-cyanated perylene diimide (PDI_CY) derivatives are molecular compounds exhibiting an uncommon combination of appealing properties, including remarkable oxidative stability, high electron affinities, and excellent self-assembling properties. Such features made these compounds the subject of study for several research groups aimed at developing electron-transporting (n-type) devices with superior charge transport performances. After about fifteen years since the first report, field-effect transistors based on PDI_CY thin films are still intensely investigated by the scientific community for the attainment of n-type devices that are able to balance the performances of the best p-type ones. In this review, we summarize the main results achieved by our group in the fabrication and characterization of transistors based on PDI8-CN2 and PDIF-CN2 molecules, undoubtedly the most renowned compounds of the PDI_CY family. Our attention was mainly focused on the electrical properties, both at the micro and nanoscale, of PDI8-CN2 and PDIF-CN2 films deposited using different evaporation techniques. Specific topics, such as the contact resistance phenomenon, the bias stress effect, and the operation in liquid environment, have been also analyzed

Correction: Space-charge accumulation and band bending at conductive P3HT/PDIF-CN₂ interfaces investigated by scanning-Kelvin probe microscopy

Correction for 'Space-charge accumulation and band bending at conductive P3HT/PDIF-CN2 interfaces investigated by scanning-Kelvin probe microscopy' by Federico Chianese et al., J. Mater. Chem. C, 2021, DOI: 10.1039/d1tc04840f

Photophysics of pentacene-doped picene thin films

Here were report a study of picene nano-cristalline thin films doped with pentacene molecules. The thin films were grown by supersonic molecular beam deposition with a doping concentration that ranges between less than one molecules of pentacene every 104 picene molecules up to about one molecule of pentacene every 102 of picene. Morphology and opto-electronic properties of the films were studied as a function of the concentration of dopants. The optical response of the picene films, characterized by absorption, steady-state and time-resolved photoluminescence measurements, changes dramatically after the doping with pentacene. An efficient energy transfer from the picene host matrix to the pentacene guest molecules was observed giving rise to an intense photoluminescence coming out from pentacene. This efficient mechanism opens the possibility to exploit applications where the excitonic states of the guest component, pentacene, are of major interest such as MASER. The observed mechanism could also serve as prototypical system for the study of the photophysics of host guest systems based on different phenacenes and acenes.Comment: 15 pages, 6 figure

Matrix-assisted pulsed laser thin film deposition by using Nd: YAG laser

Matrix-Assisted Pulsed Laser Evaporation (MAPLE) is a deposition technique, developed from Pulsed Laser Deposition (PLD) especially well suited for producing organic/polymeric thin films, which can take advantage from using Nd:YAG laser. Depending on the relative values of light absorption coefficients of the solvent and of the molecules to be deposited, laser energy is directly absorbed by the solvent or is transferred to it, providing a softer desorption mechanism with respect to PLD. In PLD ultraviolet laser radiation is commonly used, but in MAPLE, since easily damaged molecules are usually involved, the use of Nd:YAG laser offers the advantage to allow selecting laser wavelength from ultraviolet (266 nm or 355 nm, corresponding to 4.66 eV or 3.49 eV photon energies, resp.) to visible (532 nm, 2.33 eV) to infrared (1064 nm, 1.17 eV). In this paper, the MAPLE technique is described in details, together with a survey of current and possible future applications for both organic and biomaterial deposition taking into account the advantages of using an Nd:YAG laser. Beside other results, we have experimental confirmation that MAPLE applications are not limited to transparent molecules highly soluble in light absorbing solvent, thus allowing deposition of poorly soluble light absorbing molecules suspended in a light transparent liquid