An effective method for depositing highly transparent and conductive ultrathin silver (Ag) electrodes using minimal oxidation is reported. The minimal oxidation of Ag layers significantly improves the intrinsic optical and structural properties of Ag without any degradation of its electrical conductivity. Oxygen‐doped Ag (AgOx) layers of thicknesses as low as 6 nm exhibit completely 2D and continuous morphologies on ZnO films, smaller optical reflections and absorbances, and smaller sheet resistances compared with those of discontinuous and granular‐type Ag layers of the same thickness. A ZnO/AgOx/ZnO (ZAOZ) electrode using an AgOx (O/Ag = 3.4 at%) layer deposited on polyethylene terephthalate substrates at room temperature shows an average transmittance of 91%, with a maximum transmittance of 95%, over spectral range 400−1000 nm and a sheet resistance of 20 Ω sq−1. The average transmittance value is increased by about 18% on replacing a conventional ZnO/Ag/ZnO (ZAZ) electrode with the ZAOZ electrode. The ZAOZ electrode is a promising bottom transparent conducting electrode for highly flexible inverted organic solar cells (IOSCs), and it achieves a power conversion efficiency (PCE) of 6.34%, whereas an IOSC using the ZAZ electrode exhibits a much lower PCE of 5.65%.

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Advances in flexible optoelectronic devices have led to an increasing need for developing highly efficient, low-cost, flexible transparent conducting electrodes. Copper-based electrodes have been unattainable due to the relatively low optical transmission and poor oxidation resistance of copper. Here, we report the synthesis of a completely continuous, smooth copper ultra-thin film via limited copper oxidation with a trace amount of oxygen. The weakly oxidized copper thin film sandwiched between zinc oxide films exhibits good optoelectrical performance (an average transmittance of 83% over the visible spectral range of 400–800 nm and a sheet resistance of 9 Ω sq−1) and strong oxidation resistance. These values surpass those previously reported for copper-based electrodes; further, the record power conversion efficiency of 7.5% makes it clear that the use of an oxidized copper-based transparent electrode on a polymer substrate can provide an effective solution for the fabrication of flexible organic solar cells.

We demonstrate a high-performance flexible organic light-emitting diode ͑OLED͒ employing amorphous indium zinc oxide ͑IZO͒ anode. The amorphous IZO on flexible polycarbonate ͑PC͒ substrate shows similar electrical conductivity and optical transmittance with commercial ͑ITO͒ glass, even though it was prepared at Ͻ50°C. Moreover, it exhibits little resistance change during 5000 bending cycles, demonstrating good mechanical robustness. A green phosphorescent OLED fabricated on amorphous IZO on flexible PC shows maximum external quantum efficiency of ext = 13.7% and power efficiency of p = 32.7 lm/W, which are higher than a device fabricated on a commercial ITO on glass ͑ ext = 12.4% and p = 30.1 lm/W͒ and ITO on flexible PC ͑ ext = 8.5% and p =14.1 lm/W͒. The mechanical robustness and low-temperature deposition of IZO combined with high OLED performance clearly manifest that the amorphous IZO is a promising anode material for flexible displays. There has been increasing activity for flexible organic lightemitting diodes ͑OLEDs͒ over the past few years, and it has focused on developing indium tin oxide ͑ITO͒-coated polymer substrates, such as polyethylene terephthalate ͑PET͒, 1-5 polycarbonate ͑PC͒,polyimide, 8 polyethersulfone ͑PES͒, 9 polyethylene naphthalate ͑PEN͒, 9 and polycyclic olefin ͑PCO͒. 9 However, ITO electrode comes with its own set of problems such as chemical instability in a reduced ambient, poor transparency in the blue region, release of oxygen and indium into the organic layer, imperfect work function alignment with typical hole-transport layers, and easy deterioration of ITO targets. 5 In addition, the optimum properties of ITO film can only be obtained from fully crystallized film deposited at high temperature ͑ϳ300°C͒ or annealed in air or oxygen ambient. 10 With the increasing interest in the development of flexible OLEDs, there is great need for a more mechanically robust and transparent electrode because the resistance of crystallized ITO films on flexible substrate increases with increasing mechanical stain. The increase in resistance is related to the number of cracks generated in the electrode, which depends on applied strain and film thickness. 1,3 For this reason, new transparent conducting materials have been explored to replace ITO for flexible OLED anodes. To achieve better performance of flexible OLEDs, Zn-based transparent conducting oxide ͑TCO͒ films, such as ZnSn 2 O 4 , ZnSnO 3 , Zn 2 In 2 O 5 , and Al͑Ga͒-doped ZnO, have been applied as the anode.11-16 Among various Zn-based transparent conducting oxides, the Zn-doped In 2 O 3 ͑IZO͒ films recently have been recognized as promising TCO materials for OLEDs due to its good conductivity, high transparency, excellent surface smoothness, high etching rate, and low deposition temperature. [13][14][15][16] In particular, it has been confirmed that electrical and optical properties of amorphous IZO ͑a-IZO͒ films can be optimized at Ͻ50°C without a postannealing process. Therefore it is considered that a-IZO anode films can be applied to...

We report that significantly more transparent yet comparably conductive AgOx films, when compared to Ag films, are synthesized by the inclusion of a remarkably small amount of oxygen (i.e., 2 or 3 atom %) in thin Ag films. An 8 nm thick AgOx (O/Ag=2.4 atom %) film embedded between 30 nm thick ITO films (ITO/AgOx/ITO) achieves a transmittance improvement of 30% when compared to a conventional ITO/Ag/ITO electrode with the same configuration by retaining the sheet resistance in the range of 10-20 Ω sq(-1). The high transmittance provides an excellent opportunity to improve the power-conversion efficiency of organic solar cells (OSCs) by successfully matching the transmittance spectral range of the electrode to the optimal absorption region of low band gap photoactive polymers, which is highly limited in OSCs utilizing conventional ITO/Ag/ITO electrodes. An improvement of the power-conversion efficiency from 4.72 to 5.88% is achieved from highly flexible organic solar cells (OSCs) fabricated on poly(ethylene terephthalate) polymer substrates by replacing the conventional ITO/Ag/ITO electrode with the ITO/AgOx/ITO electrode. This novel transparent electrode can facilitate a cost-effective, high-throughput, room-temperature fabrication solution for producing large-area flexible OSCs on heat-sensitive polymer substrates with excellent power-conversion efficiencies.