National Institute of Materials Physics (NIMP) -CO

Dr. Anca Stanculescu-Project Director

Dr. Nicoleta Preda-scientific researcher  1

Dr. Marcela Socol-Scientific researcher 1

Dr. Oana Rasoga-Scientific researcher  2

Dr. Carmen Breazu-Scientific researcher 3

Dr. Paul Ganea-scientific researcher  3

Gabriela Petre -PhD student

"P. Poni" Institute of Macromolecular Chemistry (PPIMC)-P1

Dr. Andrei Honciuc-Partner Responsible

Dr. Ana-Maria Solonaru-Scientific researcher

Dr. Oana-Iulia Negru-Research assistant

National Institute for Laser, Plasma and Radiation physics (NILPRP)-P2

Dr. Gabriel Socol- Partner Responsible

Dr. Gianina Popescu-Pelin-Scientific researcher 3

Andreea Mihailescu-Research assistant, PhD student

Andrei Stochioiu-PhD student

Ion Tudor-technician

Stage 1: Preparation of channel active layer from new organic compounds and transparent gate electrode for OFET structures

In the frame of this stage we have synthetized and preliminary characterized organic compounds (donors and acceptors) which will be utilized in the next stages for the preparation of the channel active material in organic field effect transistor (OFET) structure.  Perylene diimides have been proposed as acceptors because of their high electrons affinity, high light absorption coefficient and good transport properties. By functionalization, in different positions, with alkyl or aryl group to the nitrogen atoms, the solubility in common solvents is improved, the segregation is prevented and the preparation of high quality thin films adequate for electronic applications (OFETs), is favored. Good absorption in visible domain and a position of the HOMO and LUMO levels favoring the charge transport which is not trap-limited, have been revealed for the selected acceptor compound that contains the alkyl substituent group.  Two arylenvinylene based monomers and intermediary monomers for the preparation of polymers with arylenvinylene and arylenethynilene structure containing 2,7-dibrom N-(2-ethyl-hexyl) were also synthetized. These compounds, showing extended absorption and good transport of the carriers, will be used as donors.

Transparent conducting oxide/TCO layers (Al:ZnO/AZO; In:ZnO/IZO90) were deposited by PLD on different flexible substrates: PES 0.25 mm, PES 0.5 mm, PET amorphous; PET biaxial oriented and flexible glass. Correlating  the morphological properties (uniform deposition) with those of transmission (>90 %) and sheet resistance (~5x10² ohm/□), the PES 0.5 mm and PES 0.25 mm substrates  can be selected for the deposition of the AZO and IZO90 transparent conductor layer.

Uni-component (donor, acceptor) and mixed donor (arylenvinylene monomer):acceptor (perylene diimide derivative) layers were prepared on the mentioned substrates using the vacuum evaporation and deposition technique. FTIR analysis has confirmed the deposition of mixed layers containing the both components and the preservation of the chemical structure of the donor and acceptor, during the deposition process. The optical analysis has revealed that, in principle, all types of substrate can be utilized for the deposition of the organic films which show absorption bands both in UV and Vis, with the exception of PES 0.25 mm which cut the signal for wavelengths <400 nm. Considering the losses by radiative relaxation mechanisms, PET amorphous, PET biaxially oriented and flexible glass have resulted as the most appropriate substrates for the deposition of simple and mixed organic layers from the selected compounds for Vis applications and flexible glass for UV applications. Correlating the transmission and photoluminescence results, the PES 0,25 mm substrate can not be used in UV domain. Taking into account, both the morphology of the layer (low roughness can reduce the scattering) and the optical properties, flexible glass is a good option of substrate for the deposition of mixed organic layers. The dielectric properties of the organic layer are not significantly affected by the type of substrate and thus they don’t have a critical role in the selection of the substrate. Considering the electrical properties of the TCO and organic layer, PES 0.5 mm and PES 0.25 mm are the most appropriate substrates for deposition. Therefore, choosing the substrate for the realization of the heterostructure it is a process that requires the consideration of several factors such as: type and properties of the TCO layer, composition and properties of the mixed layer. The substrate covered by the transparent conductor (the gate in OFET structure) must be transparent in UV and/or Vis and the organic layer must absorb the UV and/or Vis radiation that will be involved in the generation of charge carriers.

In conclusion, the objectives of this stage have been achieved: donors and acceptor compounds have been synthetized and characterized, transparent conductor layers and organic layers have been deposited on flexible substrates. The layers were characterized from morphologic, optic, electric, dielectric point of view, in order to be selected in correlation with the type of substrate. The heterostructure with mixed organic layer (monomer based on arylenvinylene):acceptor (perylendiimide) deposited on flexible AZO showed the best transport properties.

Stage 2: Realization of new nanostructured OFET structures with reproducible parameters

During this stage were investigated organic compounds from the azomethine group containing carbazole or triphenylamine groups, two polymers with an arylenevinylene structure based on 2,7 (3,6) carbazolylene-vinylene, a polymer with an arylenevinylene structure based on 2,7- dibromo-N-2-ethylhexyl carbazole (H) and the corresponding monomer 2,7-dibromo-N-2-ethyl-hexyl carbazole (MH) as donors and a non-fullerene compound, derivative of perylenediimide, studied in comparison with a fullerene derivative, as acceptor in the mixed layers for the channel of an organic field effect transistor (OFET) structure on a rigid/flexible, plan/nano-patterned substrate. Poly(arylenevinylenes) are photoluminescent conductive polymers due to the presence of single and multiple alternative bonds, but they present insolubility and infusibility that make them difficult to process. This disadvantage can be removed by intercalating N-alkyl carbazole units in the polymer structure because carbazole, like oligomers and polymers based on this monomer, have good optical and electronic properties, electrochemical reversibility, high charge carrier mobility and structural stability. Perylene tetracarboxyl diimide is used as an acceptor because its improved solubility, through functionalization with the alkyl group at the nitrogen atoms, prevents aggregation, it has good absorption in the visible and a position of the HOMO and LUMO levels favorable for carrier transport that is not limited by the phenomenon of " trapping". These mixed layers were characterized optically, morphologically and electrically, and those presenting a good UV-Vis absorption, a good transport of the charge carriers and the lowest roughness, in order to avoid losses through the scattering or recombination of the charge carriers, were selected : 1) the monomer (MH) as donor and PDI as acceptor for the bi-layer OFET structure, on a flexible nanostructured substrate; 2) polymer H as donor and PDI as acceptor to realize the bulk heterojunction active material (BHJ) for the channel of the OFET structure. To make the OFET, the layers of the structure were deposited in a well-defined sequence -the gate electrode, gate insulator, active layer, source-drain electrodes, using special masks (Ossila for OFET-low density) and a self-made  mask adaptor for vaccum evaporation equipment. To obtain the nanostructured transparent conductive electrode (AZO, IZO70, IZO90), the UV Nanoimprint Lithography method was used, generating a 2D network of nanostructures with the following geometric parameters: cylinders with a diameter of 400 nm, periodicity of 1.1, mm and  height of ~300 nm. Because the nanostructuring of a layer deposited on a flexible substrate is very difficult and because PES is the substrate that has thermal and mechanical properties that allow the processes involved in nanostructuring to be carried out, without damage, it was chosen to create flexible nanostructured OFET structures on PES. The studies for the selection of the gate insulator involved the comparative analysis of the optical-morphological and dielectric properties of three materials: poly(methyl methacrylate) and 2 nucleic acid bases, cytosine and guanine, and led to the selection of cytosine as organic material for the gate insulator. Active bi-layer OFET structures on flat and nanopatterned substrate were prepared and investigated: PETamorph/ITO_flat/cytosine/MH/PDI/Al compared to glass/IZO70_flat/cytosine/MH/PDI/Al and PES0.25 nanostructured/IZO70; IZO90; AZO/cytosine/MH/PDI/Al. Also, in advance were done the first experiments to create the OFET structure on a flexible substrate with mixed layer: PES0.25; PES0,5; PET amorph/IZO70; IZO90; AZO/cytosine/H:PDI in weight ratio (1:2)/Al. For these structures, the curves gate current=f(source-gait voltage) and drain current=f(source-drain voltage) were drawn.  The selected OFET bi-layer structure with a channel of two overlapping organic layers, on a nanostructured flexible substrate is  PES_nano/IZO90/cytosine/MH/PDI/Al, that shows small drain currents when varying the source-drain voltag, that increase by two orders of magnitude upon illumination. The properties of the OFET structures are influenced by the electrical properties of the gate insulating layer. The preliminary results indicate for the OFET structure with a bulk heterojunction channel (BHJ), on a flexible substrate, PES0.5/IZO70/cytosine/H:PDI (1:2)/Al, FET drain current=f(source-drain voltage) characteristics in the dark, with an estimated threshold voltage of ~1 V.

In conclusion, the objectives and estimated results of the phase were achieved: donor and acceptor organic compounds were synthesized, characterized and selected for the mixed layers that can be used in the realization of the bulk heterojunction (BHJ) type channel for flexible OFET. The synthesis processes have been improved with an effect on the purity and properties of the compounds. The nanostructured flexible electrode was obtained and the flexible nanostructured OFET structure with an active layer of two overlapping layers (bi-layer) was built on it. The bi-layer OFET structures were characterized and the structure that presents the best electrical behavior (PES_nano/IZO90/cytosine/MH /PDI/Al) was selected.

Stage 1 (2022)

1 paper communicated at: “7^th European Congress on Advanced Nanotechnology and Nanomaterials Webinar” November 14^th- 15th, 2022, Rome, Italy.

Title: "Organic heterostructure with dendrimer:non-fullerene mixed layer for electronic applications"

Authors: C. Breazu¹, A. Lutgarde Djoumessi Yonkeu², O. Rasoga¹, M. Socol¹, N. Preda¹, G. Petre^1,3,F. Stanculescu³, A. Stanculescu¹, E. Iwouha²

¹National Institute of Materials Physics, Atomistilor 405A, 077125, Magurele, Romania, ²University of Western Cape, Department of Chemistry, SensoLab, Robert Sobukwe Road, P. Bag X17, Bellville 7535, Cape Town, South Africa^3, University of Bucharest, Faculty of Physics, 405 Atomistilor Street, P.O. Box MG-11, Bucharest-Magurele, 077125 Romania, ⁴Laboratoire LPHIA, Université d’Angers, LUNAM 2, Bd. Lavoisier 49045, Angers, France

1 paper accepted for publication in Nanomaterials

Title: "Effect of Aluminum nanostructured electrode on the properties of bulk heterojunctions based heterostructures for electronics"

Authors: Oana Rasoga¹, Carmen Breazu¹, Marcela Socol¹, Ana-Maria Solonaru², Loredana Vacareanu², Gabriela Petre^1,3, Nicoleta Preda¹, Florin Stanculescu³, Gabriel Socol⁴, Mihaela Girtan⁵, Anca Stanculescu¹

¹National Institute of Materials Physics, 405A Atomistilor Street, P.O. Box MG-7Magurele, 077125 Romania; ²P. Poni Institute of Macromolecular Chemistry, 41 A Gr. Ghica Voda Alley, 700487, Iasi, Romania; ³University of Bucharest, Faculty of Physics, 405 Atomistilor Street, P.O. Box MG-11, Magurele, 077125 Romania; ⁴⁴National Institute for Laser, Plasma and Radiation Physics, Str. Atomistilor, Nr. 409, PO Box MG-36, Bucharest, 077125, Romania; ⁵Laboratoire LPHIA, Université d’Angers, LUNAM, 2 Bd. Lavoisier 49045, Angers, France

Stage 2  (2023)

Paper published in Thin Solid Films:

Title: Organic heterostructures based on thermal evaporated phthalocyanine and porphyrin as mixed (ZnPc:TpyP) or stacked (ZnPc/TpyP) films, Thin Solid Films, 87, 140140 (2023)

Authors: G. Petre^1,2, M. Socol¹,N. Preda¹, C. Breazu¹, O. Rasoga¹, F. Stanculescu², A. Costas¹, S. Antohe², S. Iftimie², G. Socol³, A. Stanculescu¹;

¹ National Institute of Materials Physics, 405 bis Atomistilor Street, P.O. Box MG-7, Bucharest-Magurele, 077125 Romania; ²University of Bucharest, Faculty of Physics, 405 Atomistilor Street, P.O. Box MG-11, Bucharest-Magurele, 077125 Romania; ³National Institute for Laser, Plasma and Radiation Physics, Str. Atomistilor, Nr. 409, PO Box MG-36, Magurele, Bucharest, 077125, Romania

Papers sent for publication

Title: Perylene diimide derivative based binary and ternary layers obtained by a laser technique for optoelectronic applications"; sent to Optics and Laser Technology, manuscript number: JOLT-D-23-02301 (under review).

Autori: C. Breazu¹, A. Stanculescu¹, O. Rasoga¹, N. Preda¹, A. Costas¹, A. M. Catargiu², G. Socol³, G. Popescu-Pelin², A. Stochioiu², S. Iftimie⁴, G. Petre^1,4, M. Socol¹

¹ National Institute of Materials Physics, 405 bis Atomistilor Street, P.O. Box MG-7, Bucharest-Magurele, 077125 Romania; ²P. Poni Institute of Macromolecular Chemistry, 41 A Gr. Ghica Voda Alley, 700487-Iasi, Romania;³National Institute for Laser, Plasma and Radiation Physics, Str. Atomistilor, Nr. 409, PO Box MG-36, Magurele, Bucharest, 077125, Romania; ⁴University of Bucharest, Faculty of Physics, 405 Atomistilor Street, P.O. Box MG-11, Bucharest-Magurele, 077125 Romania

Papers presented at conferences

1) EMRS Spring Meeting 2023, Symposion L: Making light matter: lasers in material sciences and photonics, 29 May-2 June, Strasbourg, France-posteTitle: Organic heterostructures with nanopatterned electrode and nanoparticle buffer layer prepared by laser technique;

Authors: C. Breazu¹, M. Socol¹, O. Rasoga¹, G. Petre^1,5, N. Preda¹, I. Zgura¹, A. Honciuc², A. M. Solonaru², G. Socol³, G. Popescu-Pelin³, M. Girtan⁴, F. Stanculescu⁵, C. Thanner⁶, A. Stanculescu¹;

¹ National Institute of Materials Physics, 405 bis Atomistilor Street, P.O. Box MG-7, Bucharest-Magurele, 077125 Romania; ²P. Poni Institute of Macromolecular Chemistry, 41 A Gr. Ghica Voda Alley, 700487-Iasi, Romania;³National Institute for Laser, Plasma and Radiation Physics, Str. Atomistilor, Nr. 409, PO Box MG-36, Magurele, Bucharest, 077125, Romania; ⁴University of Angers, Photonics Laboratory, University 2, Bd. Lavoisier 49045, Angers, France; ⁵University of Bucharest, Faculty of Physics, 405 Atomistilor Street, P.O. Box MG-11, Bucharest-Magurele, 077125 Romania; ⁶EVGroup., DI Erich Thallner Strasse 1, 4782 St. Florian am Inn, Austria .

2) EMRS Spring Meeting 2023, Simpozion Q: Advanced functional films grown by pulsed deposition methods, 29 May-2 June, Strasbourg, France-poster.

Title: Effect of laser deposited flexible transparent conductor electrode on the properties of organic heterostructures;

Authors: G. Petre¹, G. Socol², M. Socol¹, C. Breazu¹, O. Rasoga¹, N. Preda¹, P. Ganea¹, A. Honciuc³, A. M. Solonaru³, O. I. Negru³, G. Popescu-Pelin², A. Mihailescu², A. Stochioiu², F. Stanculescu⁴, A. Stanculescu¹;

¹ National Institute of Materials Physics, 405 bis Atomistilor Street, P.O. Box MG-7, Bucharest-Magurele, 077125 Romania; ²National Institute for Laser, Plasma and Radiation Physics, Str. Atomistilor, Nr. 409, PO Box MG-36, Magurele, Bucharest, 077125, Romania; ³P. Poni Institute of Macromolecular Chemistry, 41 A Gr. Ghica Voda Alley, 700487-Iasi, Romania; ⁴University of Bucharest, Faculty of Physics, 405 Atomistilor Street, P.O. Box MG-11, Bucharest-Magurele, 077125 Romania.

3)The 15^th International Conference on Physics of Advanced Materials (ICPAM 15), Topic T1: Thin Films and Nanostructures for Modern Electronics, 19-26 November 2023, Sharm El Sheikh, Egypt-invited paper.

Title: Effect of nanostructuring on the properties of organic heterostructures with single stacked bi and mixed layer;

Authors: A. Stanculescu¹, C. Breazu¹, O. Rasoga¹, G. Socol², G. Popescu-Pelin², G. Petre^1,3, M. Socol¹, F. Stanculescu³;

¹ National Institute of Materials Physics, 405 bis Atomistilor Street, P.O. Box MG-7, Bucharest-Magurele, 077125 Romania; ²National Institute for Laser, Plasma and Radiation Physics, Str. Atomistilor, Nr. 409, PO Box MG-36, Magurele, Bucharest, 077125, Romania; ³University of Bucharest, Faculty of Physics, 405 Atomistilor Street, P.O. Box MG-11, Bucharest-Magurele, 077125 Romania