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Organic light emitting diodes (OLEDs) have been attracting attention because of their advantages in emission with a wide visible region for application in fiat-panel display at low voltage and lighting[1].OLED is current injection device and the improvement of electron injection is essential for efficient and stable OLED.An efficient electron injection could be achieved by using low work function metal[2].These methods require special care and equipment for handling reactive metals and thus are less convenient for fabrication.Another commonly used is to insert an ultrathin layer as an electron-injection layer (ELL) between a metal cathode and electron transport layer (ETL).A variety of inorganic salts have been used as the buffer layers, including sodium salts or alkali metal fluorides, actually that Cs2CO3 was the best [3].