Novel approach for hole-blocking in light-emitting electrochemical cells

The light emission from solid-state conjugated polymer light-emitting electrochemical cells (LECs) has been studied when a hole-blocking layer was employed. A multilayer LEC consists of an indium-tin oxide (ITO) electrode, an emissive (EM) layer of poly (1,4-phenylenevi-nylene) (PPV) containing poly(ethylene oxide) (PEO) complexed with lithium trifluoromethanesulfonate, a hole-blocking (HB) layer of PEO complexed with poly (lithium 4-styrenesulfonate) (PSS-Li), and an aluminum (Al) electrode. The light emission intensity and external quantum efficiency of ITO/EM/HB/EM/Al cells were clearly greater than those of ITO/EM/Al cells. These results indicate that holes on the PPV main chain are trapped by immovable PSS anions and that the HB layer is effective for improving light-emitting properties of LECs.