Efficient and Spectrally Stable Blue Perovskite Light‐Emitting Diodes Employing a Cationic π‐Conjugated Polymer

Abstract

Metal halide perovskite semiconductors have demonstrated remarkable potentials in solution‐processed blue light‐emitting diodes (LEDs). However, the unsatisfied efficiency and spectral stability responsible for trap‐mediated non‐radiative losses and halide phase segregation remain the primary unsolved challenges for blue perovskite LEDs. In this study, it is reported that a fluorene‐based π‐conjugated cationic polymer can be blended with the perovskite semiconductor to control film formation and optoelectronic properties. As a result, sky‐blue and true‐blue perovskite LEDs with Commission Internationale de l'Eclairage coordinates of (0.08, 0.22) and (0.12, 0.13) at the record external quantum efficiencies of 11.2% and 8.0% were achieved. In addition, the mixed halide perovskites with the conjugated cationic polymer exhibit excellent spectral stability under external bias. This result illustrates that π‐conjugated cationic polymers have a great potential to realize efficient blue mixed‐halide perovskite LEDs with stable electroluminescence.

Multifunctional π‐Conjugated Additives for Halide Perovskite

“…observed molecules gathering areas and reduction of built‐in potential at GBs in amplitude image of electrostatic force microscopy (EFM) ( Figure 3 a,b ) when adding a p‐type π ‐conjugated polymer poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl) thiophen‐2‐yl)‐benzo[1,2‐ b :4,5‐ b ′] dithiophene))‐alt‐(5,5‐(1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethylhexyl) benzo[1′,2′‐ c :4′,5′‐ c′ ] dithiophene‐4,8‐dione))] (PBDB‐T) in antisolvent. [ 27 ] The gathering of additives around perovskite GBs was similarly observed on other conjugated molecules such as fluorinated polymer PDTBDT‐FBT (Figure 3c ), poly[(9,9‐bis(3 0‐(( N , N ‐dimethyl)‐ N ‐ethyl‐ammonium)‐propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)]di‐iodide (PFN‐I), [ 28 , 40 ] poly [(9,9‐bis(3′‐(( N , N ‐dimethyl)‐ N ‐ethylammonium)‐propyl)‐2,7‐fluorene)‐ alt ‐2,7‐(9,9‐dioctylfluorene)] dibromide (PFNBr), [ 80 ] triphenylphosphine oxides (TPPO), etc. [ 81 ] Moreover, it is found that the PeLEDs employing molecules with more phenyl groups show higher performance.…”

“…[ 122 ] Recently, PFN‐Br is reported as the ligand of blue‐emitting perovskite to benefit the hole injection and carrier transport from the GBs to the inorganic layer [PbBr 6 ] 4− of quasi‐2D perovskite. [ 80 ] In perovskite QDs, to replace the long alkyl chain ligands of oleylamine and oleic acid, conjugated molecules such as PEA, [ 123 ] 3‐phenyl‐2‐propen‐1‐amine, [ 98 ] 3,3‐diphenylpropylamine (DPPA), [ 124 ] and dodecylbenzene sulfonic acid (DBSA) [ 101 ] are employed to bond with the residual uncoordinated sites and facilitate in situ exchange on the QDs surface. Moreover, the conjugation of ligands can be enhanced to help with the formation of more effective charge carrier transport channels by the incorporation of electron‐withdrawing (‐COOH, ‐F) and electron‐donating groups (‐NH 2 ).…”

3D and 2D Metal Halide Perovskites for Blue Light-Emitting Diodes

“…Mixed-halide perovskites can be obtained via simpler synthesis routes, such as simple precursor mixing or anion exchange methods, compared with other types of blue-emissive perovskites reviewed in this paper [37,39,42]. However, one intrinsic limitation of mixedhalide perovskites is phase segregation through halide ion migration during device operation or light illumination [43][44][45][46]. The intrinsic operational instability originating mainly from halide ion migration can limit practical LED application in next-generation displays; therefore, overcoming stability issues of mixed-halide perovskites applied in blue emitters is an important challenge for researchers to resolve.…”

Phosphonate/Phosphine Oxide Dyad Additive for Efficient Perovskite Light‐Emitting Diodes

“…Metal–halide perovskite light‐emitting diodes (PeLEDs) are considered as next generation optoelectronic devices owing to their high efficiency, low cost and facile tunable optoelectronic properties [1–6] . Introduction of additives is an important strategy to improve the device efficiency of PeLEDs, and they can be divided into ionic and neutral ones [7–11] . Among neutral additives, small molecules containing ‐NH 2 , C−O−C, C=O, P=O functional groups have been studied [12–19] .…”