Ivaylo Zhivkov
Ivaylo Zhivkov
Project: OPTIMOLEL - Optimisation of thin film deposition for the molecular electronic devices
Person in Charge: doc. Ing. Martin Weiter, Ph.D.
Host institution: Institute Of Physical And Applied Chemistry, Faculty of Chemistry, Brno University of Technology
Country of Origin: Bulgaria
Project duration: 18 months
Scientific panel: Chemistry
Abstract:
Project is targeted to the development of technology for preparation of organic electronic devices such as organic solar cells, plastic lighting devices, sensors, detectors and other electronic elements. The function of these devices is based on thin active organic layers. These organic (e.g. polymer) layers are usually very thin (below 1 micrometer) and can be prepared by cheap mass production procedures such as printing. Therefore the organic electronic devices can be very cheap and thus able to compete to their standard inorganic counterpart (silicon solar cells, classic lighting devices etc.).
The main scientific and technological reason to carry out the research proposed is the necessity to improve and develop the methods for organic thin film deposition and investigation to get application level. One of the main problems to solve is the quality and reproducibility of the organic films for electronic application, the stability and the long lifetime of the devices produced. The socio-economic reason for carrying out this investigation is the great demand of new energy sources and effective lighting devices (construction of low-cost and environmentally friendly solar cells and light emitting displays).
The research proposed aimed to improve the thin film preparation by optimization of existing thin film deposition techniques (spin and deep coating, electrophoretic deposition) and introduction a novel techniques as spray deposition. It is expecting that the usage of the novel spray deposition techniques will accelerate the commercial usage of the organic semiconductors. It is also expected that the researcher’s experience in the field of electrical measurement and data acquisition and control will contribute the development the methods for materials characterization.
Photos:
1.-3. work with P.h.D students in the lab
2. Constructed electrophoretic cell and a (red colored) organic film deposited
4. Looking at the Nano World: Atom Force Microscopy (AFM) image of the films prepared, scanned area of 50x50 micrometers. Do not worry! The "himalayan hills" you saw are of less than 40 nanometers height, i. e. the height was magnified about one million times by AFM before posting here
The ongoing project summary
The project combines and focuses fifteen years experience of the researcher (Assoc. Prof. I. Zhivkov) in the physics of the organic materials with the good traditions in organic and physical chemistry of the host institution (Faculty of Chemistry, Brno University of Technology) in a way to develop, accumulate and transfer a multidisciplinary knowledge, training scientists and educate students. The main scientific project objectives are the improvement and development of the methods for organic thin film deposition and investigation to get application level of the molecular devices. The project responds the growing socio‐economic demands of development new cheap and ecological sources of energy and less energy consumers as organic solar cells and organic light emitting devices.
Project activities
Analysis of the parameters of the proposed deposition devices was performed, device block diagrams were developed and device for electrophoretic deposition was accomplished and tested. Electrophoretic cell with unmovable electrodes was developed and tested; another type of cell with movable electrodes based on previous researchers’ activity was adopted. Poly[2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylenevinylene] (MDMO‐PPV), PPV with high glass transition temperature (Tg‐PPV) and Diketopyrrolopyrroles (DPPs) materials were chosen, supporting deposition techniques as spin coating were established and deposited with both methods films were compared. A set of verification and characterization techniques for testing of the precursor solutions and suspensions and the deposited thin layers as optical spectroscopy and fluorimentry, dynamic light scattering, optical aberration method, AFM and electrical measurements were established.
Project results
It was found that parameters of the precipitation process during a suspension formation could be estimated by measurement of the peak broadening and shifting in the optical absorption and fluorescence spectra, respectively. The results were supported and refined by DLS measurement, where the suspension particle size was estimated as ca. 90 nm. The evolution of the particle size after a growing of thin films from the suspension prepared was investigated by AFM. A decreasing of the particle size in the film was observed due probably to the partial dissolving of the film from thepresented toluene in the suspension. Comparative AFM surface morphology study of electrophoretically deposited and spin coated techniques shows that the spin coated films exhibit more smooth and uniform surface. Current‐voltage measurements on ITO|MDMO‐PPV|Al structures with spin coated MDMO‐PPV films did not correlate the finest film structure and morphology with better electrical characteristics. It was found that structures with spin coated films behave more likely as photoresistors, while structures with MDMO‐PPV EPD deposited films act as solar cells. The electrical measurements performed are the first stage of investigations to get application level of the molecular devices.
Project outputs
The results obtained in the framework of the project were presented on 7 conferences (4 posters and
3 lectures), one paper was published, another paper was sent for a publication, a preparation of two
papers is in progress. The intention, activities and results are presented on created a web site of the
project http://www.facebook.com/media/set/?set=a.177088605709667.45360.177077222377472&type=1#!/pages/SoM
oPro‐SIGA‐885‐O‐P‐T‐I‐M‐O‐L‐E‐L‐project/177077222377472
A new Ph. D. position was opened and Ph. D. student was accepted under supervision of the person in charge and consultation from the researcher. Connections between the host institution and three scientific organizations from Czech Republic, some of them from South Moravian Region, and two scientific organizations from researchers’ country of residence were established. At least seven scientists were included in the measurements and training the researcher. From the other side the researcher contributes the education and training of about eight Ph. D. students and students. Two bilateral agreements for “Erasmus” student exchange were signed and three “Erasmus” students were accepted in the host institution. One Ph. D. student from the host institution visits the researchers’ country of residence. The researcher contributes for a transfer of knowledge for the electrophoretic deposition based on review of Japanese literature sources and activity towards Europe.
The ongoing project summary II
The project combines and focuses fifteen years experience of the researcher (Assoc. Prof. I. Zhvikov) in the physics of the organic materials with the good traditions in the organic and physical chemistry of the host institution (Faculty of Chemistry, VUTB) in a way to develop, accumulate and transfer a multidisciplinary knowledge, training scientists and educate students (Fig. 1). The main scientific project objectives are the improvement and development of the methods for organic thin film deposition and investigation to get application level of the molecular devices. The project responds the growing socio‐economic demands of development new cheap and ecological sources of energy and less energy consumers as organic solar cells and organic light emitting devices.
Project activities
Analysis of the parameters of the proposed deposition devices was performed, device block diagrams were developed and devices for electrophoretic and spray deposition were accomplished and tested.Electrophoretic cell with movable electrodes based on previous researchers’ activity was adopted. A previously constructed by the researcher for a commercial organization spray deposition device was provided to the host organization for educational and scientific purpose. The device was modified and upgraded as a result of the developed concepts for spray deposition. Poly[2‐methoxy‐5‐(3′,7‐dimethyloctyloxy)‐1,4‐phenylenevinylene] (MDMO‐PPV), PPV with high glass transition temperature (Tg‐PPV) and Diketopyrrolopyrroles (DPPs) materials were chosen, supporting deposition techniques as spin coating were established and deposited with different methods films were compared. A set of verification and characterization techniques for testing of the precursor solutions and suspensions and the deposited thin layers as optical spectroscopy and fluorimentry, dynamic light scattering, optical aberration method and AFM were established. Electrical measurements of structures with the organic films prepared were implemented to test the application level of the samples. It was concluded that the film deposited could be included in the future organic devices.
Project results
It was found that parameters of the precipitation process during a suspension formation could be estimated by a measurement of the peak broadening and shifting in the optical absorption and fluorescence spectra, respectively. The results were supported and refined by DLS measurement, where the suspension particle size was estimated as ca. 90 nm. The evolution of the particle size after a growing of thin films from the suspension prepared was investigated by AFM. A decreasing of the particle size in the film was observed due probably to the partial dissolving of the film from the presented toluene in the suspension. Thin films were deposited from solution with different acetonitrile concentration. The film surface roughness and root mean square from 1 to 16 nm and from 1 to 22 nm, respectively are controlled by increasing the acetonitrile amount from 50 to 90 %, which is a step towards and application level usage. Current‐voltage measurements on ITO|MDMO‐PPV|Al structures with spin coated MDMO‐PPV films does not correlate the finest film structure and morphology with better electrical characteristics. It was found that structures with spin coated films behave more likely as photoresistors, while structures with MDMO‐PPV EPD deposited films act as solar cells. A spray deposition setup was provided by the researcher to the host organization and some modifications according to the new concepts were implemented and a new software for computer controlled spray deposition was created. The device test shows stable temperature control with less than ±1ºC noise providing a linear substrate temperature gradient of about 1ºC/mm. Spray deposition of MDMO‐PPV on a glass substrate, kept in the temperature gradient shows that the MDMO‐PPV material trends to crosslinking and a formation of voids between the network fibers. Increasing the temperature reduces the void size and the covered part of the substrate increases. A spectral dependence of the photocurrent, measured without applied voltage on the electrodes results from the photogenerated charge carriers. This is a clear evidence for a potential application of the sprayed films in organic photovoltaic cells. The electrical measurements performed are the first stage of investigations to get application level of the molecular devices.
Project outputs
Spray and electrophoretic techniques for thin organic film deposition were introduced by the researcher in the host organization – staff and students were trained and teached. The results obtained in the framework of the project were presented on 7 conferences (4, posters and 3 lectures), two papers were published, another paper was submitted, a preparation of three papers is in progress. A new Ph. D. position was opened and Ph. D. Student was accepted under supervision of the person in charge and consultation from the researcher. Connections between the host institution and three scientific organizations from Czech Republic, some of them from South Moravian Region, and two scientific organizations from researchers’ country of residence were established. At least seven scientists were included in the measurements and training the researcher. From the other side the researcher contributes the education and training of about eight Ph. D. Students and Students. Two bilateral agreements for “Erasmus” student exchange were signed and three “Erasmus” students were accepted in the host institution. One Ph. D. Student from the host institution visits the researchers’ country of residence. The researcher contributes for a transfer of knowledge for the electrophoretic deposition based on review of Japanese literature sources and activity towards Europe. The activity established and developed during the project will continue. During the project the researcher opened a new activity in the host organization aiming to transfer knowledge and help in the development of computer controlled scientific experiments. After the end of the project researcher is employed at the host organization within the framework of project "Centre for Materials Research at FCH BUT" No. CZ.1.05/2.1.00/01.0012 supported by ERDF.