Doping of Tetraalkylammonium Salts in Polyethylenimine Ethoxylated for Efficient Electron Injection Layers in Solution-Processed Organic Light-Emitting Devices

Abstract

For efficient electron injection, a method to control the work functions (WFs) of ZnO electrodes in organic light-emitting devices (OLEDs) is reported in this study. First, ZnO was modified by doping of tetraalkylammonium salts (TRAX) into polyethylenimine ethoxylated (PEIE) for the WF control. Tetrabutylammonium salts (TBAX), where X = chloride, bromide, iodide, acetate, thiocyanate, and tetrafluoroborate anions, were doped into PEIE. A WF of nondoped PEIE-modified ZnO was 3.65 eV, whereas TBAX-doped PEIE-modified ZnO exhibited WFs ranging from 3.52 to 3.00 eV depending on the anion. TBAX salts exhibited different electron-donating capabilities depending on the anion, and the doping of TBAX with a large electron-donating capability exhibited a large WF reduction effect. In addition, tetraethyl- and tetrahexylammonium chlorides were doped into PEIE. PEIE doped with TRACl containing long alkyl chains exhibited a large WF reduction effect due to its low electron-accepting capabilities. In addition, the WF reduction mechanism was considered by the depth direction analysis of the PEIE:TBAX films. Finally, the ZnO/PEIE:TRAX bilayers were applied as electron injection layers in poly­[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] emissive-layer-based OLEDs with an inverted structure. The ZnO/PEIE:TBAX devices with low WFs exhibited low driving voltages.

Tailoring and Modifying an Organic Electron Acceptor toward the Cathode Interlayer for Highly Efficient Organic Solar Cells

“…One is the utilization of CIL‐induced interfacial dipole to cause the shifting of vacuum level so as to facilitate the electron extraction . Many CILs, such as poly(9,9‐bis(3′‐( N , N ‐dimethyl)‐ N ‐ethylammoinium‐propyl‐2,7‐fluorene)‐ alt ‐2,7‐(9,9‐dioctylfluorene))dibromide (PFN‐Br), polyethylenimine ethoxylated (PEIE), and poly(vinylpyrrolidone) (PVP), are developed based on the strategy of interfacial dipole. However, although these CILs have significantly enhanced the OSC efficiencies, they can only work well in ultrathin films due to the low electron mobility; this excludes their applications from the high‐throughput production of printing processing where certain thickness variation is unavoidable .…”

Air-Stable Ultrabright Inverted Organic Light-Emitting Devices with Metal Ion-Chelated Polymer Injection Layer

“…In addition, the maximum efficiencies of device ZnO/PEI are inferior to those of device PEI and device PEI-Zn (see Table S1 and the reason is discussed in the later). As noted above, device PEI-Zn shows much better high-brightness performances compared to device PEI, device ZnO/PEI and previously reported inverted OLEDs [9,10,12,13,[23][24][25][26][27][28][29][30].…”

Low‐Work‐Function PEDOT Formula as a Stable Interlayer and Cathode for Organic Solar Cells

“…In contrast, an obvious peak appeared at 402.3 eV in PEDOT:PSS-TBA, corresponding to the N element in tetraalkylammonium cations. [28] Because of the similar doping level, the PEDOT:PSS and PEDOT:PSS-TBA should have similar optical properties. [29] The absorption of PEDOT:PSS and PEDOT:PSS-TBA in Figure 2F was acquired by counting the transmittance and reflectance (as shown in Figure S5A,S5B, Supporting Information).…”