Light‐Emitting Electrochemical Cells with Polymer‐Blended InP/ZnSeS Quantum Dot Active Layer

Abstract

A light‐emitting electrochemical cell (LEC) is an innovative device with a simple structure wherein a mixture of a luminophore and an electrolyte is sandwiched between electrodes. Here, LECs are presented which contain an active layer composed of green‐emitting InP/ZnSeS quantum dots (QDs) blended with polyvinyl carbozole p‐type polymer semiconductors and 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid (IL). The blending of QDs with polymer semiconductors increases the density of holes reaching the QDs; this, in turn, leads to luminescence from QDs, which is unachievable without the presence of polyvinyl carbazole semiconductor. Moreover, the deposition of a zinc oxide nanoparticle layer onto the QD–polymer–IL active layer increases the density of electrons reaching the QDs. The composition of these materials is varied systematically for balancing the injection rates of electron versus hole into the QDs. A luminance of ≈632 cd m−2 and an efficiency of >1.3 cd A−1 are achieved.

High‐Performance Narrowband Light‐Emitting Electrochemical Cells Enabled by Intrinsically Ionic Multi‐Resonance Thermally Activated Delayed Fluorescence Emitters

“…In doped films, they show narrowband green-blue TADF emission with high photoluminescent efficiencies (Φ PL ) at ≈90%. LECs using an ionic exciplex host and the ionic MR-TADF guest emitters show narrowband green-blue EL with high EQEs up to 10.0% at 6.0 V. With ionic TADF small-molecule hosts, the LECs deliver high EQEs up to 13.0% at 4.0 V, which to the best of our knowledge is the highest among all narrowband LECs (including those based on quantum dots [41][42][43][44][45] or perovskites [42,[46][47][48][49][50][51][52][53][54] ) reported so far. Moreover, the LECs show peak brightness/EQE/half lifetime at 917 cd m −2 /6.3%/5.3 h or 780 cd m −2 /5.6%/62.2 h at 50 A m −2 .…”

“…Figure S15 (Supporting Information) shows the current efficiency versus brightness curves for the LECs driven at 5.0 V. The peak efficiencies reached at 99 and 137 cd m −2 for LEC-4 and LEC-5, respectively. Under a lower driving voltage of 4.0 V, LEC-4 afforded an even higher peak EQE of 13.0% at 41 cd m −2 (Figure S16, Supporting Information; Table 3), which is the highest among all narrowband LECs (including those based on quantum dots [41][42][43][44][45] or perovskites [42,[46][47][48][49][50][51][52][53][54] ) reported so far. Figure S17 (Supporting Information) shows the current-density and brightness versus voltage curves and the EQE versus brightness curves for the LECs under voltage-sweeping driving.…”

“…Narrowband LECs based on quantum dots or perovskites have been developed for nearly 10 years. [41][42][43][44][45][46][47][48][49][50][51][52][53][54] LECs with a single active layer of quantum dots usually show unsatisfactory efficiencies. [41] Su et al inserted a cationic iridium complex layer as the hole injection/transport layer in red-emitting quantum-dot LECs to improve the device performance, achieving high EQEs up to 9.7% under constant-voltage driving.…”

Perovskite Light‐Emitting Electrochemical Cells Employing Electron Injection/Transport Layers of Ionic Transition Metal Complexes

“…However, significant loss in device efficiency and complicated fabrication processes hinder their application potential. On the other hand, recently reported inorganic LECs based on QDs [25][26][27][28][29] and perovskites [30][31][32][33][34][35][36][37] intrinsically exhibit saturated EL spectra that is suitable for display applications. Compared with QDs, perovskites show wider color tunability (ultraviolet to near-infrared) by simply adjusting the halide composition.…”