Flexible organic light emitting diode on bacterial cellulose substrate with transparent electrospun web anode.


Project Director: Dr. Iulia Corina Ciobotaru

Abstract

The project brings together three new technologies: a) the using of modified bacterial cellulose for FLOEDs substrates by improving the transparency and mechanical properties. This type of technology covers the flexibility class of materials in which the glass substrates are removed from the future electroluminescent diodes. Besides this aspect, the future of the FOLEDs opens new perspectives in the optoelectronic area; b) applying the electrospun web technology for the FOLEDs anodes to increase the light output of these devices. The appliance of this technology will offer an alternative of the brittle and expensive indium tin oxide, allowing the improvement of the rolling technologies for the displaying and lightening domain; c) integrating of the new organometallic compound with dual electroluminescence as emissive layer and comparison with the commercial one. The strategy consists of using a freestanding sandwich structure with successively deposited organic layers onto a transparent electrospun metallic web as an anode. Thus, this structure will be easily attached to the glass and BC composite membrane by thermal transfer to obtain either OLEDs and FOLEDs devices. A comparison between the luminance of the FOLEDs and OLEDs will be performed related to the transparency of the BC substrate and electrospun web anode. The level of the involved technologies will be tested and validated in laboratory conditions as a functional system while the performances will be highlighted in comparison with classical technologies.

Objectives

Objective 1. Obtaining a freestanding sandwich structure by successive deposition of the organic layers onto an electrospun metallic web and characterization of the OLEDs.
Objective 2. Optimization of BC membranes as flexible substrates for FOLEDs applications.
Objective 3. Integration of the component structures in FOLEDs and characterization of the performances of the devices.
Objective 4. Comparison between FOLEDs and OLEDs structures.

Coordinator - INSTITUTUL NATIONAL DE CERCETARE - DEZVOLTARE PENTRU FIZICA MATERIALELOR BUCURESTI RA.
Partner 1 - INSTITUTUL NATIONAL DE CERCETARE - DEZVOLTARE CHIMICO - FARMACEUTICA - I.C.C.F. BUCURESTI.

  1. Dr. Iulia Corina Ciobotaru - project leader - INCDFM.
  2. Dr. Constantin Claudiu Ciobotaru - research member - INCDFM.
  3. Dr. Silviu Polosan - research member - INCDFM.
  4. Dr. Alexandru Evanghelidis - research member - INCDFM.
  5. Dr. Angela Casarica - person in charge from partener 1 - ICCF - Bucuresti
  6. Dr. Cristina Balas (Sturzoiu) - research member partener 1 - ICCF-Bucuresti.

 

Stage 1- summary

Stage 1 of the project entitled “ Flexible organic light emitting diode on bacterial cellulose substrate with transparent electrospun web anode” (Acronym: FOLEDBCtransWEB) (PN-III-P2-2.1-PED-2019-1459, no. 484PED⁄2020) includes the first activity from within the first work package entitled "Obtaining a freestanding sandwich structure by successively depositing the organic layers onto an electrospun metallic web and characterization of the OLEDs”.

The results of the preparation and characterization of the metalized electrospun transparent fibers are highlighted during the scientific and technical description of the first activity in the project.

During this activity, a series of PMMA samples were made, deposited by the electrospinning process, and covered with metallic layers of gold, silver, and ITO to obtain metalized webs that will act as an anode for FOLED devices. The optical properties of these fibers were highlighted by optical transmission measurements. Their morphology was highlighted by SEM analysis, and the electrical properties were analyzed by four-point probe measurements to determine the sheet resistance of the metal layer. During this stage, it was possible to select the optimal fibers regarding their mechanical properties and conduction depending on the deposited metal. Thus, the best results were obtained on gold-coated PMMA fibers, which will later be used as anodic layers because it has high electrical conduction even at low fiber densities (high optical transmissions), as well as a band alignment, suitable for the next p-type conductive polymer layer.

Stage 2 – summary

Stage 2 of the project entitled “ Flexible organic light-emitting diode on bacterial cellulose substrate with transparent electrospun web anode” (Acronym: FOLEDBCtransWEB) (PN-III-P2-2.1-PED-2019-1459, no. 484PED⁄2020) includes the activities from within the first work package entitled "Obtaining a freestanding sandwich structure by successively depositing the organic layers onto an electrospun metallic web and characterization of the OLEDs” and also the activities from the “WP2. Preparation and characterization of transparent BC membrane substrates”.

In task no. 2.1, the fabrication of “free-standing” self-supporting devices was made by successively depositing the organic layers on the metalized and optimized PMMA fibers from the stage 1. The activity of obtaining PMMA fibers was resumed in this stage as well, to optimize the final free-standing structure, after the deposition of the organic layers. In this context, PMMA fibers with optical transmissions between 25-90% were obtained on which an anodic layer of gold with different thicknesses was deposited. Organic p-type conductive polymers (Hole Transport Layer -HTL) with different chemical structures were deposited on these fibers: PEDOT-PSS, TPD, PVK, benzanthracene, as well as organometallic compounds emissive layers: Alq3, Ir (ppy)3 and IrQ (ppy)2. In the end, the cathodic layer of LiF/Al was deposited. Each layer deposition also led to a selection of the fibers obtained (from a total of 350 samples), depending on the optical transparency to ensure a successful deposition of all the layers in the device.

The gold anodic layers were deposited by Magnetron Sputtering, the conductive polymer layers were deposited by cyclic voltammetry (PEDOT-PSS) and by thermal evaporation Alq3, IrQ(ppy)2, Ir(ppy)3, and the LiF/Al cathode.

Each layer was characterized, as appropriate, by optical methods (UV-Vis, Raman, FT-IR, luminance), morphological (SEM), electrical, and the thickness of the layers was determined by AFM and cross-SEM measurements.

In task no. 2.2. it will be considered the assembly of these optimized layers in order to obtain a free-standing device and its transfer on a glass substrate for performing the electrical measurements.

Activity 2.3 represents the first activity from the second work package of the project. A second key element of the project is introduced in this work package, bacterial cellulose produced by the ICCF-Bucharest partner. For the execution of the activity, the research team of ICCF Bucharest, used the implemented biotechnological methodologies, by patent No. RO126940 / 30.09.2013, entitled “Biotechnological process for obtaining bacterial cellulose on mixed substrates” whose authors are Angela Casarica, Radu Iulia Corina, and all. The manufacture of transparent composite membranes involved the same biotechnological processes of obtaining native bacterial cellulose membranes, as well as obtaining bacterial cellulose membranes functionalized in situ (by adding directly to the culture medium PVA solution) and ex-situ (direct functionalization by immersion/impregnation of bacterial cellulose membranes in epoxy / acrylic thermosetting resins) These techniques aimed to obtain membrane/film products with a higher level of transparency.

The ex-situ process emphasizes the composite membranes with transparency similar to that of native products, and the composite membranes with improved transparency were obtained by in-situ functionalization.

These composites membranes were characterized by optical methods (UV-Vis, FT-IR), structural (SEM), and thermal (DSC) in activity 2.4. Activity 2.5 performed the deposition of a SiO2 thin layer as a barrier against humidity, a fact that was highlighted by optical and structural measurements.

 

 

  • C. Ciobotaru, C.C. Ciobotaru, M. Beregoi, A. Evanghelidis, S. Polosan, I. Enculescu - “Electrospun fibers electrodes coated with conductive polymers for FOLED applications”- 14th International Symposium on Flexible Organic Electronics (ISFOE21) 5-8 July 2021, Thessaloniki, Greece – poster
  • Mihaela Beregoi, Alexandru Evanghelidis, Corina Ciobotaru, Ionut Enculescu – “Flexible electrodes based on metalized electrospun fiber networks” - Nanofibers, Applications and Related Technologies, 8-10 SEPTEMBER 2021, Istanbul Technical University – oral presentation.
  • Iulia Corina Ciobotaru, Silviu Polosan, Monica Enculescu, Andrei Nitescu, Ionut Enculescu, Mihaela Beregoi, Constantin Claudiu Ciobotaru*, “Charge transport mechanisms in free-standing devices with electrospun electrodes”- Nanotechnology – submitted ISI article

Dr. Corina Ciobotaru, PhD in Chemical Engineering

Scientific Researcher III

National Institute of Materials Physics

Multifunctional Materials and Structures Laboratory

Telephone: +40-(0)21-2418 268


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