Flexible and Transparent Electrodes of Cu 2− X Se with Charge Transport via Direct Tunneling Effect

In this paper, it is demonstrated that copper selenide (Cu 2− X Se) films onto polyester sheets may serve as transparent electrodes in inorganic–organic hybrid light emission devices (IOHLED), as possible replacement to indium tin oxide or fluorine‐doped tin oxide. The Cu 2− X Se film synthesized via bath chemical deposition is electrically stable with a sheet resistance of 148 Ω sq −1 and optical bandgap of 2.3 eV. IOHLED are made with poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS) as an organic layer for hole transport and poly[2‐metoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH‐PPV) as electroluminescent semiconductor. The IOHLED emits in the visible range owing to the simultaneous emission from Cu 2− X Se and MEH‐PPV layers. The enhanced performance is explained by analyzing the charge transport mechanisms at the inorganic–organic interface, which for Cu 2− X Se/PEDOT:PSS changes from Fowler‐Nordheim to direct tunneling regardless of the device temperature (90–370 K). The onset voltage is 75% smaller than in the absence of the PEDOT:PSS layer due to a 27 meV decrease in the potential barrier, and the direct tunneling becomes more relevant to device performance than the sheet resistance of the Cu 2− X Se layer. Upon adding transparency, mechanical flexibility, and covering large areas, the ultrathin Cu 2− X Se films on polyester substrates permit new designs for electro‐optical devices with inorganic–organic heterojunctions.