HYBRID EVENT: You can participate in person at Tokyo, Japan or Virtually from your home or work.
Cristian Ravariu, Speaker at Speaker for Green Chemistry Conferences: Cristian Ravariu
University Politehnica of Bucharest, Romania
Title : Green chemistry offers non-carcinogenic organic semiconductors for thin film transistors


Few successful semiconductors used in Organic Thin Film Transistors (OTFT) are pentacene, tetracene, Alq3. However, these traditional organic semiconductors are based on polycyclic aromatic hydrocarbons (PAHs) as precursors, with a high toxic - carcinogenic potential during the technological processing. Therefore, we present in this work, OTFT with green compounds grafted on the Nano Core Shell (NCS) nanomaterials, appealing to green chemistry synthesis routes. For the experimental synthesis of semiconductor for OTFT, we consider ferrite nano-core with organic external shells: paraaminobenzoic acid (PABA) for p-type films and sulpho-salicilic acid (SSA) for n-type films. A review paper from 2015 classified all semiconductor oxides after their bandgap energy, TiO2 (EG=3.2eV), ZnO (EG=3.2eV), Fe3O4 (EG=2.2eV). So, the ferrite nanoparticles with minimum bandgap is an excellent candidate for optimum electronic conduction. The PABA molecules grafted to the external shell of ferrite nano-core shell (PABA-NCS) nanoparticles have been investigated by DLS, FT-IR, SEM, TEM, while the electrical measurements of transistors based on PABA-NCS films have assessed the potential use of this material in p-type organic semiconductor transistors. The synthesis of PABA-NCS nanoparticles is accomplished by the co precipitation method, as reported in 2020. The fabrication of glass substrate / ITO / Polystyrene / PABA-NCS uses
the dip coating technique. This structure has been immediatly operated as an electronic device, by placing two thin probes onto the top of PABA-NCS film, as the Source and Drain contacts, and ITO electrode as Gate contact, based on the pseudo- Metal-Oxide-Semiconductor (pseudo-MOS) transistor technique. The measured currents at VGS = -20V and VSD = 1V for three structures indicated the saturated drain current: 202nA, 14nA and 0,045nA, respectively for PABA-NCS-600nm, 400nm and 200nm. Another non-toxic organic compound, acting as donor of electrons, is Sulpho-Salicylic Acid (SSA). It can be attached to the external shell of ferrite nano-core (Fe3O4), providing SSA-NCS nanoparticles, by self-assembling technique. Our equation provides the electrons mobility of μn,sat = 0.45cm2/Vs in this OTFT biased to VG = 10V and VDS > Vdsat. This value is superior than μn,sat = 0.054cm2/Vs, in n-film OTFT with Pentacene, reported elsewhere. A short discussion concerns the low toxicity of the SSA-NCS compound. By degradation ferrite can generate Fe+, O- ions, usually encountered in human body and environment. The lethal dose LD50 for SSA was established to 700 mg/kg, while LD50 of PAH (like benzo[k] fluoranthene) is 14 μg/kg. On the other hand, the SSA precursor is the salicylic acid, a veritable green compound that acts as plant hormone or vascular drug.

Audience Take Away:
• Explain how the audience will be able to use what they learn? - The audience will be able to contemplate to use traditional organic semiconductors with toxic PAH precursors or not. We start to demonstrate that PABA-NCS and SSA-NCS are green nanomaterials suitable for OTFT.
• Is this research that other faculty could use to expand their research or teaching? Does this provide a practical solution to a problem that could simplify or make a designer’s job more efficient? The audience will be able to use our ideas to develop clean technologies for organic electronics. The simple techniques like dip coating or co-precipitation - are easily to be implemented in faculties labs, too.


Prof. C. Ravariu studied Microelectronics at the Polytechnic University of Bucharest, Romania and graduated as MS in 1993. He worked as scientific researcher first 5 years at Institute of Microtechnology, Bucharest, then joined the Polytechnic University of Bucharest. After multiple foreign stages in Bioelectronics (Patras, Greece), Nano-devices (EPFL, Switzerland), Organic Electronics (LAAS, France), he received PostDoc degree in 2012 in Romania. Since 2013, he obtained the position of Full Professor at the Polytechnic University of Bucharest, Faculty of Electronics, Romania. He has published more than 250 research articles. Since 2014, he is Chairman of the Romanian IEEE Electron Devices Chapter.