Perovskite Light‐Emitting Diodes with Improved Outcoupling Using a High‐Index Contrast Nanoarray

Abstract

Metal halide perovskite light-emitting diodes (PeLEDs) have gained significant interest for next-generation optoelectronic devices, since PeLEDs exhibit narrow emission bandwidth that allows for vivid and clear images based on their high color purity. [1][2][3][4][5][6] The emission color of PeLEDs is tunable in the visible and near-infrared (NIR) spectral regions and they offer low operating and turn-on voltages, along with promising efficiency values. [3,4,[7][8][9] In addition, thin films have shown nearunity photoluminescence quantum yield (PLQY) and population inversion at room temperature, [10][11][12][13][14] potentially allowing for electrically pumped lasers with various emission colors.There has recently been rapid growth in the external quantum efficiency (EQE) of PeLEDs, to values of over 20%, [9,[15][16][17][18][19][20][21][22][23][24][25][26][27] since early reports of PeLEDs in 2014 with efficiency below 0.25%. [28] Numerous strategies to improve the EQE of PeLEDs are being actively pursued in order to bring their performance in line with other, more established, LED technologies. [8] However, a disparity of refractive index (n) between organic transport layers (typically in the range of 1.6-1.8) and the perovskite emissive layer (≈2.3 near the emission wavelength) holds back performance. [29][30][31][32] Due to the high n of the perovskite layer, the maximum EQE of PeLEDs is limited by outcoupling efficiency and restricted to ≈20%, with the remainder of light being trapped within the thin film and substrate materials, as well as parasitic absorption. [31,32] Therefore, it is necessary to investigate alternative device architectures that are able to enhance outcoupling efficiency and realize direct benefits to EQE.In this study, we demonstrate EQE of 14.6% in methylammonium lead iodide (MAPbI 3 ) based red/NIR LEDs using a randomly distributed nanohole array (NHA) embedded in a SiN layer between the indium tin oxide (ITO) anode and glass substrate. The SiN layer with a high n of 2.02 at the peak emission wavelength possesses a high-index contrast with the voids of the NHA with n of 1.0. This layer effectively compensates for the high n of the perovskite emissive layer and aids outcoupling of waveguided and substrate modes. As a result, PeLEDs with NHAs show 1.64 times higher light extraction than PeLEDs without NHAs. Figure 1a displays the device structure of PeLEDs with and without NHAs, as well as the molecular structures of transport Organic-inorganic hybrid perovskite light-emitting diodes (PeLEDs) are promising for next-generation optoelectronic devices due to their potential to achieve high color purity, efficiency, and brightness. Although the external quantum efficiency (EQE) of PeLEDs has recently surpassed 20%, various strategies are being pursued to increase EQE further and reduce the EQE gap compared to other LED technologies. A key point to further boost EQE of PeLEDs is linked to the high refractive index of the perovskite emissive layer, leading to optical losses of more than 70% of ...

High‐Efficiency Perovskite Light‐Emitting Diodes with Synergetic Outcoupling Enhancement

“…The transmittance haze corresponds to the percentage of light diffusely scattered compared to the total light transmitted, and an increase in haze represents the stronger light scattering in the patterned ZnO and ZnO/PEDOT:PSS layers. It is thus expected that the presence of patterned ZnO and ZnO/PEDOT:PSS layers can redirect the light transmission, leading to the considerable opportunity for outcoupling enhancement of waveguided light in MEN‐patterned PeLEDs . In addition, Figure shows clearly that the haze value for the patterned ZnO/PEDOT:PSS in the whole visible wavelength region is lower than that for only patterned ZnO.…”

Light extraction from quantum dot light emitting diodes by multiscale nanostructures

“…This is due to the large difference of the refractive index between the glass substrate and the air medium. 32,33 Compared with the controlled device, a large amount of the internally conned light will be effectively extracted from the glass substrate due to the attaching of multiscale PDMS nanostructures. Fig.…”

Influence of indium-tin-oxide and emitting-layer thicknesses on light outcoupling of perovskite light-emitting diodes

“…As a result, external quantum efficiency (EQE) as high as 20% has been achieved in PeLEDs in contrast to the first PeLED in 2014, which had less than 1% efficiency [3, 17–19]. However, the overall EQE of PeLEDs is still low since more than 70% of the photons generated are dissipated within the device [20–22]. The reason is strongly linked to the mismatch of the refractive index ( n ), between the perovskite emitting layer (EML, typically in the range of 2.0–2.3) and the other transporting layers (typically 1.6–1.8) in the multi-layered device.…”

“…This discrepancy induces internal light reflections at the interface of the layers that restrict the outcoupling of PeLEDs. Therefore, improving the light outcoupling is an essential challenge to overcome [18, 19, 22–25].…”

“…Using the internal structure of the EML, Cao et al reduced the waveguide optical losses and achieved a maximum EQE as high as 20% for the first time [19]. Another strategy is to extract photons from the substrate by using additional structures inside it [22, 24]. Desirable nanostructures with a proper difference in n can effectively help a large portion of confined photons to be outcoupled to the air, resulting in considerable improvements in EQE.…”