Organic Light-Emitting Diodes || Infrared Organic Photodetectors || Light Up-conversion Devices || Organic Solar Cells
Organic Light-Emitting Diodes

An Organic Light Emitting Diode (OLED) is an LED whose emissive layer comprises of organic materials. These materials are usually either polymers or small molecules. Generally polymers are made into thin films by spin coating and small molecules are evaporated.

The OLED technology is the most mature technology based on organic materials. Full-color displays based on fluorescent and phosphorescent OLEDs and PLEDs are already in commercial production. OLEDs have already found there way in commercial market as cell phone, mp3 players and car stereo displays and it is believed that many more unconventional applications of OLED will be out in the market soon such as flexible, roll-able and bendable displays. OLEDs are particularly suited for these applications because of their better readability in sunlight and their low power consumption. Also OLEDs can be used as backlights in flat-panel displays for light weight and low power advantages.

Apart from display applications, OLEDs also demonstrate great potential for solid state lighting applications such as general space illumination, and large-area light-emitting elements. OLEDs are wide area light sources and they typically emit less light per unit area than their inorganic counterparts, which are usually point-light sources.

In our laboratory, the research efforts are mainly geared towards fabricated high efficiency phosphorescent white emitting OLEDs utilizing novel materials and new device architectures. Our OLED team fabricated world record high efficiency blue phosphorescent device which was highlighted on DOE website as well as several other news websites:

We further use these high efficiency blue phosphorescent OLEDs for fabricating high efficiency white OLED devices. the picture shown below shows the approach we follow in our lab for fabrication of high efficiency white PHOLEDs


Infrared Organic Photodetectors

Organic thin film photodiodes have attracted great interest for use in organic photovoltaic cells and organic photodetectors. Recently, organic photodetectors with high quantum efficiency of over 70% have already been reported. Their compatibility with lightweight, rugged, or flexible plastic substrates opens up many applications that cannot be addressed using other conventional detector technologies. However, organic photodetectors, which were reported up to now, have showed the limited photosensitive spectra of visible range wavelength. Therefore, the realization of organic photodetector with infrared (IR) sensitivity can extend the applications of organic electronics to large area sensing and detection. Our group explores a wide variety of materials and device structures for realizing infrared organic photodetectors.

Light Up-conversion Devices

Light up-conversion devices have attracted a great deal of research interest because of their potential applications in night vision, range finding, and security as well as semiconductor wafer inspections. Early near infrared (NIR) up-conversion devices were mostly based on heterojunction structures of inorganic semiconductors. However, the up-conversion efficiencies of these devices were very low. Recently, NIR-to-visible light up-conversion devices, which integrate an inorganic light-emitting diode (LED) with an inorganic photodetector, have been reported but the maximum external conversion efficiency was about 0.3%. In addition to low efficiencies, inorganic up-conversion devices are expensive to fabricate for large area applications.

In recent years, both high-efficiency OLEDs and high-efficiency organic photodetectors have been demonstrated. All organic up-conversion devices can be realized by integrating an OLED and an organic photodetector into one device. Because of their compatibility with lightweight, ruggedness, and flexible plastic substrates, all organic up-conversion devices open up many applications that cannot be realized using conventional technologies.

Organic Solar Cells

In meeting the challenge of the energy crisis facing the world, harvesting energy from sunlight offers a viable solution. In this context, solar cells based on organic materials are considered a promising alternative to their inorganic counterparts for the generation of affordable, clean, renewable energy. Other than cost-effectiveness, these organic devices have several additional attributes including greater mechanical flexibility, light weight, aesthetically pleasing colors, and the potential for transparent embodiments which open up novel application possibilities. With steady improvement in efficiency this technology is nearing the benchmarks for commercialization. In our lab, we apply a three-pronged approach in the research of organic based solar cells. In collaboration with our partners in chemistry, we employ new polymers and small organic molecules, with untapped functionalities, in fabricating high-performance solar cells. For example, we are studying color-tunable and broadly absorbing donor-acceptor polymer systems as viable photovoltaic polymers. At the same time, we implement new architectural modifications to maximize the performance of these devices. In this area, we are studying the role interfacial modifications on device efficiency. Finally, we study the device physics to investigate the fundamental operation mechanisms and the processes limiting their performance to enable further rational optimization.