Light Out‐Coupling Management in Perovskite LEDs—What Can We Learn from the Past?

Abstract

The research on perovskite light‐emitting diodes (PeLEDs) has experienced an exponential growth in the past six years. The highest external quantum efficiencies (EQEs) have surpassed 20%, 20%, and 10% for red, green, and blue colored LEDs, respectively. Considering the internal quantum efficiency is already approaching unity owing to the high material quality, the limiting factor for further improving the EQE is mainly the poor light out‐coupling efficiencies. Here, by reviewing the progress on the light out‐coupling studies for PeLEDs, organic LEDs (OLEDs), conventional semiconductor LEDs, and other special LEDs, the rational design guidelines are summarized for enhancing PeLED out‐coupling. Briefly, these design guidelines include: 1) introducing nanostructures into the active layer or tuning the thickness of it to couple out the waveguide modes, 2) adding nanostructures between the active layer and transparent electrodes to couple the waveguide modes to substrate modes, 3) adding nanostructures such as nanowires to the glass substrate to couple the substrate mode to air. Essentially, these guidelines indicate that implementing nanophotonic engineering on PeLEDs is a highly promising direction to explore, so as to substantially enhance the device performance.

Strategies Toward Efficient Blue Perovskite Light‐Emitting Diodes

“…In planar LEDs, it is a big challenge to enhance the light out-coupling efficiency due to the various permittivities of dielectric and metal thin film multilayers, which result in near 80% of the light generated by the emitters being trapped inside the device. [129,130] Thus, there is a strong aspiration to improve the device performance by enhancing the light out-coupling efficiency. The construction of periodic micro-nanostructures on the device was accepted as an efficient way to improve the light out-coupling efficiency.…”

Strategies to Improve Luminescence Efficiency and Stability of Blue Perovskite Light‐Emitting Devices

“…[ 87 ] Meng et al demonstrated that the device structure consisting of transparent electrode/high‐index transport layer/perovskite emitter/low‐index transport layer/reflective electrode could raise η out to 12.0%, 17.5%, and 31.2% for blue, green, and red PeLEDs by reducing the optical loss in surface plasmon and waveguide mode. [ 86 ] Therefore, the low η out leaves considerable opportunity for a substantial boost in EQE of blue PeLEDs if the optical loss can be efficiently suppressed, including waveguide mode, [ 86,88–97 ] surface plasmon mode, [ 98–105 ] and substrate mode. [ 101 ]…”

“…Many techniques have been implemented for the light outcoupling enhancement for various LED technologies, including the use of photonic structure at the appropriate device interfaces, refractive‐index coupling layers, microlens arrays, diffraction gratings, and so on. [ 86,88–107 ] Jeon et al used a randomly distributed nanohole array (NHA) embedded in a SiN x layer between ITO and glass substrate to facilitate the outcoupling of the waveguide mode ( Figure a). [ 106 ] High‐efficiency red/near‐infrared PeLEDs with an EQE max of 14.6% were realized (Figure 6b).…”

Giant Enhancement of Radiative Recombination in Perovskite Light-Emitting Diodes with Plasmonic Core-Shell Nanoparticles

“…Apart from material and structure optimization, different approaches are widely explored to improve the quality and performance of PeLEDs, including recent advances in nanophotonics [ 16 , 17 , 18 ]. For example, surface patterning leads to enhanced light outcoupling and photon recycling [ 19 , 20 , 21 , 22 , 23 ] which is beneficial for PeLEDs.…”