title: High Current Injection into Dynamic p-n Homojunction in Polymer Light-Emitting Electrochemical Cells.
abstract: Ions and electrons in blends of polymer-electrolyte can work in ensemble to operate light-emitting electrochemical cells (LECs), in which the unique features of in situ formed p-n homojunctions offer efficient charge injection and transport. However, electrochemical features give rise to significant stability and speed issues due to limited electrochemical stability and low ion mobility, resulting in low brightness and a slow response of LECs. Here, these issues are overcome by the separate control of ionic and electronic charges, using a simple driving pulse superimposed on a small base voltage; ions with slow response are rearranged by a constant base voltage, while a high-voltage pulse, superimposed upon the base, injects electrons/holes which have fast response, with minimal effect on the ions. This scheme successfully injects an extremely high current density of > 2 kA cm-2with a balanced electron/hole ratio, at a high-speed response time of ≈ 50 ns; both properties demonstrate advantages of LECs in making polymers brighter. An in situ electron spin resonance measurement on the LECs further revealed that this impressive performance is due to the highly doped polymers, whose spin density reached 7 × 1019spins cm-3, and an ordered polymer structure in the active layer blend.
authors.affiliation: Department of Applied Physics, Nagoya University, Chikusa, Nagoya, 464-8603, Japan.
authors.forename: Tomo
authors.initials: T
authors.lastname: Sakanoue
authors.affiliation: Department of Applied Physics, Waseda University, Tokyo, 169-8555, Japan.
authors.forename: Jinpeng
authors.initials: J
authors.lastname: Li
authors.affiliation: Department of Applied Physics, Nagoya University, Chikusa, Nagoya, 464-8603, Japan.
authors.forename: Hisaaki
authors.initials: H
authors.lastname: Tanaka
authors.affiliation: Department of Applied Physics, Waseda University, Tokyo, 169-8555, Japan.
authors.forename: Ryota
authors.initials: R
authors.lastname: Ito
authors.affiliation: Central Research Institute of Electric Power Industries (CRIEPI), 2-6-1, Nagasaka, Yokosuka, 240-0196, Japan.
authors.forename: Shimpei
authors.initials: S
authors.lastname: Ono
authors.affiliation: Department of Applied Physics, Nagoya University, Chikusa, Nagoya, 464-8603, Japan.
authors.forename: Shin-Ichi
authors.initials: SI
authors.lastname: Kuroda
authors.affiliation: Department of Applied Physics, Nagoya University, Chikusa, Nagoya, 464-8603, Japan.
authors.forename: Taishi
authors.initials: T
authors.lastname: Takenobu
keywords: ionic liquids; light-emitting electrochemical cells; organic laser diodes; semiconducting polymers