Origin of Enhanced Hole Injection in Inverted Organic Devices with Electron Accepting Interlayer

Abstract

Conventional organic light emitting devices have a bottom buffer interlayer placed underneath the hole transporting layer (HTL) to improve hole injection from the indium tin oxide (ITO) electrode. In this work, a substantial enhancement in hole injection efficiency is demonstrated when an electron accepting interlayer is evaporated on top of the HTL in an inverted device along with a top hole injection anode compared with the conventional device with a bottom hole injection anode. Current–voltage and space‐charge‐limited dark injection (DI‐SCLC) measurements were used to characterize the conventional and inverted N,N′‐diphenyl‐N,N′‐bis(1‐naphthyl)(1,1′biphenyl)‐4,4′diamine (NPB) hole‐only devices with either molybdenum trioxide (MoO3) or 1,4,5,8,9,11‐hexaazatriphenylene hexacarbonitrile (HAT‐CN) as the interlayer. Both normal and inverted devices with HAT‐CN showed significantly higher injection efficiencies compared to similar devices with MoO3, with the inverted device with HAT‐CN as the interlayer showing a hole injection efficiency close to 100%. The results from doping NPB with MoO3 or HAT‐CN confirmed that the injection efficiency enhancements in the inverted devices were due to the enhanced charge transfer at the electron acceptor/NPB interface.

Dual roles of MoO3-doped pentacene thin films as hole-extraction and multicharge-separation functions in pentacene/C60 heterojunction organic solar cells

“…[19][20][21][22] In particular, transition metal oxides (i.e., MoO 3 ) doped organic semiconductor demonstrated special merits on improving device performance and stability. [23][24][25][26][27][28] In this letter, we report the improved performance including V oc and short-circuit current density (J sc ) simultaneously, in a pentacene/C 60 heterojunction OSC by using thin MoO 3 -pentacene film as the anode interfacial layer and the MCS layer, respectively. Compared with non-doped device, PCE is improved from 0.97% to 2.29%.…”

N1,N1,N3,N3-tetra([1,1′-biphenyl]-4-yl)-N5,N5-diphenylbenzene-1,3,5-triamine: Synthesis, optical properties and application in OLED devices as efficient hole transporting material

“…No light emission was detected from the hole-only devices during the measurement, implying that the electron was not injected and recombined with the hole. From the SCLC measurements, the zero field mobility of NPB was determined to be 2.15 Â 10 À4 cm 2 V À1 s À1 , which is consistent with values from literature [37,38]. The mobility of TDAB-BP (2.09 Â 10 À3 cm 2 V À1 s À1 in Table 1) is nearly one order of magnitude higher than that of NPB, which could be an alternative material to NPB and contribute to the better performance of OLEDs.…”

Efficient small molecule-based bulk heterojunction photovoltaic cells with reduced exciton quenching in fullerene

“…FF and V oc values in BHJ cells with MoO 3 or PEDOT: PSS buffers are close therefore the BHJ cell with PEDOT: PSS buffer gives an improved PCE of 6.26%. HAT-CN is an n-type organic semiconductor, but it can be used as the hole-extraction layer in organic light emitting devices [18][19][20]. Two-compound anode buffer layers, 5 nm MoO 3 /5 nm HAT-CN and PEDOT: PSS/5 nm HAT-CN, are also employed in DBP: C 70 BHJ cells for comparison.…”