Sky-Blue-Emissive Perovskite Light-Emitting Diodes: Crystal Growth and Interfacial Control Using Conjugated Polyelectrolytes as a Hole-Transporting Layer

Chung Hyeon Jang; Amit Kumar Harit; Seungjin Lee; Su Hwan Kim; Ji-Eun Jeong; Jong Hyun Park; Eui Dae Jung; Jung Min Ha; Sang Kyu Kwak; Han Young Woo; Myoung Hoon Song

doi:10.1021/acsnano.0c04968

Sky-Blue-Emissive Perovskite Light-Emitting Diodes: Crystal Growth and Interfacial Control Using Conjugated Polyelectrolytes as a Hole-Transporting Layer

ACS Nano. 2020 Oct 27;14(10):13246-13255. doi: 10.1021/acsnano.0c04968. Epub 2020 Sep 18.

Authors

Affiliations

¹ School of Materials Science and Engineering, Ulsan National Institute of Science and Technology (UNIST), UNIST-gil 50, Ulsan 44919, Republic of Korea.
² Department of Chemistry, Korea University, Seoul 02841, Republic of Korea.
³ Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4, Canada.
⁴ Department of Energy Engineering and School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), UNIST-gil 50, Ulsan 44919, Republic of Korea.

PMID: 32910640
DOI: 10.1021/acsnano.0c04968

Abstract

A series of poly(fluorene-co-phenylene)-based anionic conjugated polyelectrolytes (CPEs) are prepared with varying sizes of counterions (tetramethylammonium, tetraethylammonium, and tetrabutylammonium (TBA⁺)) and studied as a hole-transporting layer (HTL) for sky-blue-emissive perovskite light-emitting diodes (PeLEDs). Ionic CPE HTLs improve the wettability, compatibility, and nucleation of perovskite crystals at interfaces, enabling highly crystalline perovskite crystal growth with enhanced light-emitting properties. By incorporating the CPE HTLs containing bulky TBA⁺ counterions (MPS2-TBA) in place of PEDOT:PSS, the decreased phonon-electron coupling and increased exciton binding energy in perovskites are measured by temperature-dependent photoluminescence (PL) measurements. By increasing the size of counterions in CPE interlayers, the PL intensities and lifetimes of perovskite films increase. Through space-charge-limited current measurements, the lowest trap density is measured in the perovskite film on MPS2-TBA, emphasizing a critical role of larger counterions. Using density functional theory, MPS2-TBA is calculated to show the strongest adsorption affinity toward the interstitial defect of lead ions, explaining its pronounced interfacial defect passivation. The counterion size in CPE interlayers is interpreted as a main factor to determine the adsorption affinity onto perovskite, which determines the interacted area as noncovalent adsorption occurs. Finally, the sky-blue-emissive quasi-2D PeLED with MPS2-TBA shows the highest luminance efficiency (a peak EQE of 2.6% at 489 nm) and significantly improved spectral stability.

Keywords: conjugated polyelectrolytes; crystal growth; defect passivation; hole-transporting layers; sky-blue-emissive perovskite light-emitting diodes.