Thermally-induced degradation is widely recognized as a performance-limiting obstacle to the development of organic light-emitting-diodes (OLEDs) with longer lifetime and higher brightness, two essential requirements for continued commercial development. The work proposed here will tests a new means of re-engineering OLEDs for improved thermal performance based on the implementation of a direct, high resolution thermal imaging technique capable of measuring temperature profiles with a fine spatial and thermal resolution across the light-emitting surface of OLEDs.
Broader impact:
We envision a long-term overall goal of engineering organic and quantum dot photonic devices for improved performance. This proposal will significantly enhance the infrastructure for research and education at Mt Holyoke College, by creating a novel facility for the fabrication of organic and nanoscale optoelectronic devices.
The project has developed a new imaging technique that will greatly expand researchers’ ability to understand the inner workings of the next generation of solar cells, light emitting diodes and flexible transistors. The imaging technique is capable of non-destructively observing heating inside an operating solar cell or light emitting diode, allowing researchers to pin point the occurrence of trouble spots, poor film quality or degradation, which will show up as anomalously hot or cold regions inside the device. Because the measurements are accomplished using visible light, high resolution imaging is possible, and encapsulation layers, glass or other films will not affect the measurement’s accuracy. These capabilities amount to a more powerful engineering and scientific tool for the measurement of heating in optoelectronic devices than any other technique currently in use. This project will help bring organic light emitting diode (OLED) technologies to market faster by improving our ability to understand the processes that limit the lifetime of OLEDs. OLED lighting and OLED displays have the capability to reduce power consumption while improving color rendering, as compared to current technology. Lighting accounts for a large portion of electricity use in buildings and homes, and therefore a relatively small improvement in efficiency can translate to huge energy savings worldwide. OLED lighting could offer improved color at a lower cost than traditional fluorescence and LED lighting, likely encouraging more people to transition away from inefficient incandescent lighting. OLED displays offer exceptional color quality and faster response times, a powerful incentive for consumers to switch to this more efficient technology. This project has contributed to the establishment of an organic device fabrication facility at Mount Holyoke College; to the best of our knowledge this is the first of its kind at a small liberal arts college, providing a unique opportunity for Mount Holyoke’s women undergraduates to develop hands on device design and fabrication skills. The physical resources of the college have been further enhanced by the development of a thermoreflectance microscopy lab for high resolution 3D thermal imaging. This project has provided opportunities for women and minority undergraduates to participate in cutting edge experimental research. Of the more than 20 students, three postdoctoral scholars and one graduate student who have participated in this research project this reporting period, all but three are women. Beyond the field of organic optoelectronic devices, we have demonstrated a new capability to image charge carries in organic transistors, and this capability is likely to be transferable to solar cells and LEDs as well. Tracking carrier concentration as a function of voltage under typical operating conditions is likely to have a direct impact on our understanding of the fundamental operation of these devices. It is also possible that electric field measurements can be performed at a much higher resolution and with greater differentiation between layers than standard electroabsorption techniques.
