This invention explores ways to make Organic Light Emitting Diodes (OLEDs) emit more light and be more efficient. OLEDs create light through particles called singlet excitons. However, only about 25% of these particles produce light directly, while the other 75% do not. This limits the OLED's efficiency. To overcome this, certain mechanisms, like Thermally Activated Delayed Fluorescence (TADF) and Triplet-Triplet Annihilation (TTA), are used to convert non-light-emitting particles into light-emitting ones. The focus here is on improving a specific type of OLED made from polymers, called Polymeric LEDs (PLEDs). By designing these PLEDs to better manage and convert excitons, we can significantly boost their light output and efficiency.
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- Energy Efficiency: PLEDs are more energy-efficient than traditional lighting technologies like incandescent bulbs and even fluorescent lamps. The high EQE (17-18%) of the prototype means it can produce the same amount of light with less electricity consumption, potentially reducing energy bills for consumers and lowering overall energy demand.
- PLEDs do not contain mercury or other hazardous materials found in traditional fluorescent lamps, making them environmentally friendly over their lifecycle.
- Concept demonstrated can be used for molecular engineering as well.
- Utilizing Thermally Activated Delayed Fluorescence (TADF) and Triplet-Triplet Annihilation (TTA) mechanisms, the OLED improves singlet exciton yield. This leads to increased radiative recombination, thereby boosting Electroluminescence (EL) and Photoluminescence (PL).
- The combination of a zinc oxide (ZnO) electron injection layer and a barium hydroxide (Ba(OH)2) hole blocking layer forms an efficient cathode terminal. This setup, along with MoO3/Au as the Ohmic hole injection contact, ensures effective charge carrier injection and transport.
- The OLED generates singlet and triplet excitons in a controlled ratio of 1:3 at the cathode terminal. These excitons decay exponentially towards the anode, enhancing the overall efficiency of the device.
- The molecular design includes predetermined steric hindrance, causing minimization of orbital overlap which helps to prevent singlet-triplet interactions and annihilation. This design strategy increases the excited state lifetime of triplet excitons, allowing them to convert into singlet excitons more efficiently at room temperature.
- EQE (Enhanced Quantum Efficiency) is measured across different current densities, showing a peak EQE that exceeds the theoretical spin statistical limit. The analysis indicates that minimizing the spatial overlap of donor and acceptor orbitals and reducing the singlet exciton lifetime can mitigate STA, thereby improving EQE.
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The prototype has achieved an external quantum efficiency (EQE) of 17-18% and a luminance efficiency of approximately 30 cd/A. The concept has been successfully demonstrated using a single pixel emitting green light. However, it can be scaled up for full displays utilizing backplane thin-film transistors (TFTs) and other colours.
Display and Lighting Devices, Electronics
Display and lighting devices