The purity of OLED materials is one of the most important factors affecting the performance of organic light-emitting diode (OLED) devices. This not only has a direct impact on OLED performance, but also on its reliability and stability - and therefore the lifetime of the devices. In fact, the purity of an OLED material directly impacts device charge (electron and hole) transport capacity. It plays a crucial role in ensuring that an organic electronic device performs satisfactorily.
Wöhrle et al. investigated the impact of material purity on photovoltaic performance . They showed that non-sublimated materials resulted in a rougher surface on the thin film, causing pinholes to emerge. This resulted in short circuits that deteriorated the device performance. Salzman also proved that the PCE of copper phthalocyanine (CuPc)-based OPV devices could be enhanced more than five-fold when the donor material was efficiently purified . It was further pointed out that the lower-purity thin film also exhibited low carrier-mobility, leading to a small fill factor (FF).
Liu has also demonstrated that the power conversion efficiency was improved from 2.7% to 4.3% by the sublimation of SubPc. Atomic-force microscopic images showed that the crystallinity was improved with sublimed SubPc, leading to significantly enhanced hole-mobility of SubPc in orders of magnitude, as estimated by the space-charge limited current .
Sublimation is a technique used to obtain ultra pure-grade chemicals by removing trace metals, inorganic and volatile impurities. Sublimation happens under certain pressure for chemicals to only go through two physical stages: from a solid state to vapour (gas), and when the vapour condenses to a solid state on a cool surface (referred to as cold finger deposition). The most typical examples of sublimation are iodine and dry ice. Sometimes multiple sublimation is needed for even higher levels of purity.
With our collection of high-purity sublimed materials, you can have confidence in your experiment results, boost the lifetime and the stability of your built devices - and most importantly, the purity of the colour display and your device performance.
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- Investigations of n/p-junction photovoltaic cells of perylenetetracarboxylic acid diimides and phthalocyanines, D. Wöhrle et al., J. Mater. Chem., 5, 1819-1829 (1995), DOI: 10.1039/JM9950501819.
- The effects of copper phthalocyanine purity on organic solar cell performance, R. F. Salzman et al., Org. Electronics, 6, 242-246 (2005), doi:10.1016/j.orgel.2005.09.001.
Efficient Organic Photovoltaic Device Using a Sublimated Subphthalocyanine as an Electron Donor, S. Liu et al., ECS Solid State Lett., 1 (5), 70-72 (2012), doi: 10.1149/2.002205ssl.
Interesting fact: Sublimation happens to the snow on the top face of Mt. Everest due to low temperatures, strong winds, intense sunlight and very low air pressure -- a perfect recipe for sublimation to occur!