A device includes a first electrode and a second electrode, an active layer between the first electrode and the second electrode and a plurality of auxiliary layers between the first electrode and the active layer. The auxiliary layers include first and second auxiliary layers, the first auxiliary layer proximate to the active layer, the second auxiliary layer proximate to the second electrode. An energy level of the active layer, an energy level of the first auxiliary layer, an energy level of the second auxiliary layer, and a work function of the first electrode become deeper sequentially or shallower sequentially.