Fluorene copolymer bilayers for emission colour tuning in inverted hybrid light emitting diodes

Abstract

© The Royal Society of Chemistry 2015.We present a robust, entirely solution-based processing route for the deposition of planar F8BT/TFB poly(9,9-dioctylfluorene-alt-benzothiadiazole)/poly(9,9-dioctylfluorene-alt-N-(4-butylphenyl)-diphenylamine) emissive/hole transport bilayers for emission colour tuning in inverted organic-inorganic hybrid light emitting diodes (HyLEDs). Our method allows the facile exploration of TFB thickness for the first time within inverted devices; here we describe the influence of TFB thickness on the device performance. In particular, we demonstrate significant variations in device electroluminescence with highly controlled tunability between green and orange (550 to 610 nm) emission; correlating directly with the thickness of the TFB layer. These changes are in parallel with a 20-fold increase in current efficiency with respect to F8BT-only devices, with our bilayer devices exhibiting luminance values exceeding 11 000 cd m^-2. Additionally, through reflectance and angle-dependent electroluminescence measurements we explore the presence of microcavity effects and their impact on device behaviour. We introduce TFB not only as a charge blocking/transporting layer but also as an optical emission-tuning layer

Charge‐Carrier Density Independent Mobility in Amorphous Fluorene‐Triarylamine Copolymers

“…Despite a relatively long scan time, the diffractogram showed no diffraction peaks, the spectrum being dominated by the background due to the glass substrate (we note that F8BT fi lms show clear diffraction peaks under the same experimental conditions with the same apparatus (see the Supporting Information of ref. [ 33 ] )). This is consistent with XRD results for TFB and other fl uorene-triarylamine copolymers, which show no evidence of any crystalline phase.…”

“…Fluorene-triarylamine copolymers are specifi cally designed to be amorphous, with high glass transition temperatures, for use as interlayer and hole transport layer materials in polymer light emitting diodes. [31][32][33][34][35][36][37] They have also been used, along with the homopolymer poly(triarylamine), as p-type semiconductors in OFETs, allowing highly uniform charge transport over large-area substrates, an important requirement for applications such as display backplanes. [ 38 ] Their charge transport has been extensively studied in bulk diodes using the time-of-fl ight (TOF) and transient SCLC dark injection (DI) techniques, [39][40][41][42] and modeled in the low chargecarrier density regime using the GDM, correlated GDM, and polaronic correlated GDM.…”

Highly Efficient Inverted Circularly Polarized Organic Light-Emitting Diodes

“…20 The shape of the electroluminescence (EL) spectrum can be impacted by the interlayer thickness in bilayer PLEDs due to the associated change in reflectance, overall device optics and position of the recombination zone (RZ). 34 To minimize these changes, we investigated the device performance of CP-PLEDs with 5 -40 nm TCTA HTL (ZnO/PEIE/F8BT+10%[M] (180 nm)/TCTA (of variable thickness)/MoO x /Au; Figure S5). The thickness range was chosen in order to maintain the EL shape of devices and simplify the device optics involved in CP-PLED.…”

Organic-inorganic hybrid composites as an electron injection layer in highly efficient inverted green-emitting polymer LEDs

“…The 9wt% CPE:ZnO NP EIL has a smooth, dense morphology with good coverage, facilitating homogeneous electron injection and hole blocking, both of which are desirable for device performance. [25,27] Secondly, the inclusion of the CPE in composite EILs leads to a desirable shift in workfunction.…”