Efficient electron transfer between a cathode and an active organic layer is one key to realizing high-performance organic devices, which require electron injection/transport materials with very low work functions. We developed two wide-bandgap amorphous (a-) oxide semiconductors, a-calcium aluminate electride (a-C12A7:e) and a-zinc silicate (a-ZSO). A-ZSO exhibits a low work function of 3.5 eV and high electron mobility of 1 cm 2 /(V · s); furthermore, it also forms an ohmic contact with not only conventional cathode materials but also anode materials. A-C12A7:e has an exceptionally low work function of 3.0 eV and is used to enhance the electron injection property from a-ZSO to an emission layer. The inverted electron-only and organic light-emitting diode (OLED) devices fabricated with these two materials exhibit excellent performance compared with the normal type with LiF/Al. This approach provides a solution to the problem of fabricating oxide thin-film transistor-driven OLEDs with both large size and high stability.inverted OLEDs | electron injection | electron transport | amorphous oxide semiconductor | low work function material E lectronic and photonic devices based on organic semiconductors have attracted much attention due to their intrinsic characteristics that are difficult to achieve in inorganic semiconductors, such as flexibility and the capability of precise molecular design of active organic layers (1-3). However, organic devices suffer from the material properties that organic semiconductors in general have: rather high lowest unoccupied molecular orbital (LUMO) levels and low electron mobilities, such as 10 −6 to 10 −3 cm 2 /(V·s). This leads to inefficiency in electron injection/transport between an electrode and an organic active layer and a large energy loss. In other words, the creation of materials suitable for efficient electron injection layers (EILs) and electron transport layers (ETLs), with very low work functions, reasonable chemical stability, and high electron mobility, should lead to organic devices with improved performance.Organic light-emitting diodes (OLEDs) are regarded as nextgeneration flat-panel displays (4). Although small high-resolution OLED displays are used widely for smart phones/tablets, and large televisions are being commercialized, several issues still remain, such as lifetime, image sticking, power consumption, and production cost (5). The recent high-resolution OLED pixels (6) with reduced aperture ratios [areal ratio of thin-film transistor (TFT) to pixel] raise the importance of the top emissiontype structure for practical use. For large OLEDs, it is unrealistic to use low-temperature polycrystalline silicon (LTPS) TFTs for backplanes. Only oxide TFTs, as represented by a-In-Ga-Zn-O (a-IGZO) (7), are practical candidates for the backplane (8, 9). The current small OLEDs use normal-type structures combined with p-channel LTPS TFTs. However, only n-channel TFTs are possible for oxide TFTs in actual applications. Simple substitution of the p-channel LTPS TFTs wi...