Efficient Spin-Light-Emitting Diodes With Tunable Red to Near-Infrared Emission at Room Temperature

Abstract

Spin light-emitting diodes (spin-LEDs) are important for spin-based electronic circuits as they convert the carrier spin information to optical polarization. Recently, chiral-induced spin selectivity (CISS) has emerged as a new paradigm to enable spin-LED as it does not require any magnetic components and operates at room temperature. However, CISS-enabled spin-LED with tunable wavelengths ranging from red to near-infrared (NIR) has yet to be demonstrated. Here, chiral quasi-2D perovskites are developed to fabricate efficient spin-LEDs with tunable wavelengths from red to NIR region by tuning the halide composition. The optimized chiral perovskite films exhibit efficient circularly polarized luminescence from 675 to 788 nm, with a photoluminescence quantum yield (PLQY) exceeding 86% and a dissymmetry factor (g_lum) ranging from 8.5 × 10^-3 to 2.6 × 10^-2. More importantly, direct circularly polarized electroluminescence (CPEL) is achieved at room temperature in spin-LEDs. This work demonstrated efficient red and NIR spin-LEDs with the highest external quantum efficiency (EQE) reaching 12.4% and the electroluminescence (EL) dissymmetry factors (g_EL) ranging from 3.7 × 10^-3 to 1.48 × 10^-2 at room temperature. The composition-dependent CPEL performance is further attributed to the prolonged spin lifetime as revealed by ultrafast transient absorption spectroscopy.

Keywords: chiral perovskite; circularly polarized electroluminescence; red and NIR‐LED; spin funneling; spin‐LED.

Figure 1

The characteristics of R‐NEA₂(FA_0.8MA_0.2)₂Pb₃Br_{(10‐ x )}I _x (x = 6, 7, 7.5, 8, 8.5, 9, 9.5) perovskite films. a) Electrostatic potentials of the EDTMP passivant. b) Schematic illustration of quasi‐2D perovskites. c) Absorption spectra. d) PL spectra. e) PXRD patterns and standard XRD cards of MAPbBr₃, MAPbI₃, FAPbBr₃ and FAPbI₃ perovskites. f) PLQY.

Figure 2

CD spectra a) and g _CD spectra b) of R/S‐NEA₂(FA_0.8MA_0.2)₂Pb₃Br_0.5I_9.5 films. CPL spectra of R/S‐NEA₂(FA_0.8MA_0.2)₂Pb₃Br_{(10‐ x )}I _x films, x = 7 c); x = 8 e); x = 9.5 g) and g _lum of R/S‐NEA₂(FA_0.8MA_0.2)₂Pb₃Br_{(10‐ x )}I _x films, x = 7 d); x = 8 f); x = 9.5 h).

Figure 3

a) Transient absorption (TA) spectrum color maps of R‐NEA₂(FA_0.8MA_0.2)₂Pb₃Br₂I₈ thin film. b) TA spectra at different decay times. c) Decay kinetics at different wavelengths. Transient kinetics (3D resonant pump conditions) for the same‐circularly (SC) and counter‐circularly (CC) polarized pumps and probes of R‐NEA₂(FA_0.8MA_0.2)₂Pb₃Br_{(10‐ x )}I _x , x = 6 d), x = 8 e), x = 9.5 f). Transient kinetics (pump at 3.1 eV) for the same‐circularly (SC) and counter‐circularly (CC) polarized pumps and probes of R‐NEA₂(FA_0.8MA_0.2)₂Pb₃Br_{(10‐ x )}I _x , x = 6 g), x = 8 h), x = 9.5 i). j) Schematic diagram of energy and spin funneling process that transfers spin‐polarized excitons from 2D to 3D phase in different chiral perovskite films.

Figure 4

The device structure and EL performance of spin‐LEDs using S‐NEA₂(FA_0.8MA_0.2)₂Pb₃Br_{(10‐ x )}I _x (x = 6, 7, 7.5, 8, 8.5, 9, 9.5) perovskites. a) Device structure. b) Schematic diagram of the energy levels of spin‐LEDs. c) EL spectra at 6 V. d) Current density‐voltage characteristics. e) EQE‐current density characteristics. (Insert is the photograph of the x = 8 device operating at 6 V). f) Luminance‐voltage characteristics of red devices (x = 6, 7, 7.5) and radiance‐voltage characteristics of NIR devices (x = 8, 8.5, 9, 9.5). CPEL spectra of spin‐LEDs based on R/S‐NEA₂(FA_0.8MA_0.2)₂Pb₃Br_{(10‐ x )}I _x perovskites, x = 7 g), x = 8 h), x = 9.5 i) and g_EL of spin‐LEDs based on R/S‐NEA₂(FA_0.8MA_0.2)₂Pb₃Br_{(10‐ x )}I _x perovskites, x = 7 j), x = 8 k), x = 9.5 l).