Final Report Summary - BLEND (Stability of blended organic semiconductors under various environments)
Electronics is a very fast developing field of industry; its impact on many areas of commercial and industrial production has increased tremendously. The main focus, especially in commercial products, has for several years been steered towards smaller size, increased amount of functionality, higher reliability, and lower price. There is a significant and competitive electronics industry in Europe. However, it faces global pressures and in order to succeed it has to be able to produce enhanced products at lower cost. Organic semiconductors are one of the new material systems to having extensive potential for new and innovative products. They offer several advantages over inorganic semiconductors, such as silicon, including lightness, mechanical robustness, and ease of manufacturing, which makes them competitive alternatives for new innovative products such as organic light emitting diodes (OLED), organic field-effect transistors (OFET), organic photovoltaics (OPV), and flexible displays. However, organic semiconductor materials suffer from relatively low stability, which results in severe use restrictions due to reliability issues. Consequently, it is essential that more research activities in the field of organic semiconductors are focused on their stability and how to improve it. In this project the goal has been to find new ways to improve stability of these materials through blending and to create methodologies for testing and studying their stability issues.
The objects of the project have:
• To characterise the properties of organic semiconductors blended with stable commodity insulating polymer materials and to study the stability of such materials.
• To develop testing protocols to determine the stability of the developed blended material systems using systematic environmental testing.
• To calculate acceleration factors for the material systems
The aim of this project has been to provide a deeper insight and new information concerning the stability of organic semiconductor multicomponent systems comprising at least one insulator component. One of the key objectives has been to gain understanding about how these materials behave under different conditions as encountered in the final product. In addition, one of the aims has been to calculate acceleration factors for these materials and to study how different materials systems behave compared to each other.
The first year of the project concentrated on development of processes and measurement techniques for organic semiconducting polymers blended with commodity polymers. The characterisation techniques studied included transmission optical microscopy, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV-Vis), and photoluminescence (PL). Of the studied techniques FTIR, UV-Vis, PL and optical microscopy were found to be suitable for the morphology and stability studies. Additionally, aging techniques for films of semiconductor polymer blends were developed. The work in the project has concentrated on ambient, dark conditions. Especially, the project work concentrated on the effect of humidity as this has been studied very little with neat organic semiconducting materials.
The second year of the project concentrated on the stability studies. Several different combinations of organic semiconductors with insulating polymers were studied. In order to study the morphology of these systems annealing studies with different casting temperatures were conducted with them. This research concentrated especially on polyethylene (PE), Poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl butyric acid methyl esters (PCBM). Such systems may be used in organic photovoltaics. The results of these studies showed the importance of the materials on the morphology. By using different material and annealing combinations the morphology of the films could be greatly modified. The research also showed that PE may cause long-term reliability issues due to the clustering of PCBM. The casting temperature was also found to be critical for the film morphology. This area has not been widely studied and therefore further studies are needed how it affects the behaviour of devices.
To study the long-term stability of the devices several different aging levels were studied. This was needed to calculate the acceleration factors of the materials. Overall, four different aging temperatures were used. The results clearly showed that the rate of degradation increased markedly with the increase of the aging temperature. To calculate the changes caused by the degradation in the materials UV-Vis absorption of the films was used. The UV-Vis absorption of the films decreased during aging and this could be used to calculate acceleration rate for the degradation. These rates were used with Arrhenius equation to calculate activations energies for various material systems. The results showed that the addition of insulating polymer affected the behaviour of the films. However, the stability of the films was not markedly better with insulating polymers and therefore, such systems cannot be used to improve the stability of the devices. However, the results clearly showed that the insulating polymer affected the long-term behaviour of the films which needs to be considered if such systems are used in organic electronics devices.
In addition to the thermal aging, in the project the effect of humidity was studied. Although the effect of humidity in devices with organic semiconductors has been widely studied, the effect of humidity on neat materials has been studied very little. The results of the project showed that the behaviour of semiconducting polymers in humid conditions is very different from dry conditions. When devices with organic semiconducting polymers have been studied, humidity has been found to be a major issue. However, with neat films the humidity did not increase the degradation rate and the humidity actually seemed to protect the materials from degradation. This is an interesting result which needs to be further studied.
The objects of the project have:
• To characterise the properties of organic semiconductors blended with stable commodity insulating polymer materials and to study the stability of such materials.
• To develop testing protocols to determine the stability of the developed blended material systems using systematic environmental testing.
• To calculate acceleration factors for the material systems
The aim of this project has been to provide a deeper insight and new information concerning the stability of organic semiconductor multicomponent systems comprising at least one insulator component. One of the key objectives has been to gain understanding about how these materials behave under different conditions as encountered in the final product. In addition, one of the aims has been to calculate acceleration factors for these materials and to study how different materials systems behave compared to each other.
The first year of the project concentrated on development of processes and measurement techniques for organic semiconducting polymers blended with commodity polymers. The characterisation techniques studied included transmission optical microscopy, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV-Vis), and photoluminescence (PL). Of the studied techniques FTIR, UV-Vis, PL and optical microscopy were found to be suitable for the morphology and stability studies. Additionally, aging techniques for films of semiconductor polymer blends were developed. The work in the project has concentrated on ambient, dark conditions. Especially, the project work concentrated on the effect of humidity as this has been studied very little with neat organic semiconducting materials.
The second year of the project concentrated on the stability studies. Several different combinations of organic semiconductors with insulating polymers were studied. In order to study the morphology of these systems annealing studies with different casting temperatures were conducted with them. This research concentrated especially on polyethylene (PE), Poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl butyric acid methyl esters (PCBM). Such systems may be used in organic photovoltaics. The results of these studies showed the importance of the materials on the morphology. By using different material and annealing combinations the morphology of the films could be greatly modified. The research also showed that PE may cause long-term reliability issues due to the clustering of PCBM. The casting temperature was also found to be critical for the film morphology. This area has not been widely studied and therefore further studies are needed how it affects the behaviour of devices.
To study the long-term stability of the devices several different aging levels were studied. This was needed to calculate the acceleration factors of the materials. Overall, four different aging temperatures were used. The results clearly showed that the rate of degradation increased markedly with the increase of the aging temperature. To calculate the changes caused by the degradation in the materials UV-Vis absorption of the films was used. The UV-Vis absorption of the films decreased during aging and this could be used to calculate acceleration rate for the degradation. These rates were used with Arrhenius equation to calculate activations energies for various material systems. The results showed that the addition of insulating polymer affected the behaviour of the films. However, the stability of the films was not markedly better with insulating polymers and therefore, such systems cannot be used to improve the stability of the devices. However, the results clearly showed that the insulating polymer affected the long-term behaviour of the films which needs to be considered if such systems are used in organic electronics devices.
In addition to the thermal aging, in the project the effect of humidity was studied. Although the effect of humidity in devices with organic semiconductors has been widely studied, the effect of humidity on neat materials has been studied very little. The results of the project showed that the behaviour of semiconducting polymers in humid conditions is very different from dry conditions. When devices with organic semiconducting polymers have been studied, humidity has been found to be a major issue. However, with neat films the humidity did not increase the degradation rate and the humidity actually seemed to protect the materials from degradation. This is an interesting result which needs to be further studied.