The Current Outlook for Perovskite Light Emitting Diodes
Perovskites are an alternative material platform to silicon with tunable optoelectronic properties.
Perovskites enable unique LED architectures that are not available on planar silicon, such as thin-film LEDs and flexible LEDs.
Integration of perovskite light emitting diodes into traditional electronics occurs at the board level and does not require special circuitry.
Perovskite light emitting diodes may take this form factor one day
After looking at the progress around silicon as a material platform for solar cells, LEDs, and other standard semiconductors, it’s hard to imagine an alternative for optoelectronics. Components like photodiodes and LEDs have been built from a small range of alternative semiconductors, but there are other exotic materials that hold promise for use in optoelectronic components. Examples include metal oxides, polymers, photonic crystals, and perovskites.
Among these alternatives, perovskites have received significant attention and are on the cusp of commercialization. Three major areas where perovskites are used in developing new optoelectronics are in light emitting diodes, photodetectors, and solar cells. Among these areas, perovskite light emitting diodes are unique, as they fill a gap in the capabilities of silicon, namely that silicon’s indirect bandgap has made it challenging to build an LED operating with any useful efficiency.
Thanks to significant progress in perovskite material research, product designers have access to a solution-processable material platform for tunable thin-film LEDs. Keep reading to learn more about perovskite light emitting diodes and how to integrate them into your optoelectronics systems.
Materials for Perovskite Light Emitting Diodes
Perovskites are a class of optoelectronic materials that have the general chemical formula ABX3, where A and B are distinct cations, and X is an anion. In addition, these materials have a specific crystal structure that matches the structure of perovskite minerals, where BX6 octahedra are surrounded by a cubic, tetragonal, or orthorhombic lattice of A atoms in a single unit cell. The general chemical structure of perovskites has enabled a range of material combinations involving metals, organic compounds, and inorganic compounds.
The structure of these materials can be quite complex, particularly those used for perovskite light emitting diodes. However, tunability of the structure is necessary to produce a material with the desired optoelectronic properties. Some of the major perovskite material platforms for LEDs include:
Oxide-based: Perovskite minerals are oxide-based compounds that contain two metal cations bonded to oxygen atoms in the standard ABX3 chemical formula. These materials are ferroelectric and are less often used for optoelectronic or photovoltaic applications.
Metal halides: These materials see wide usage in optoelectronic devices. In the chemical formula for these perovskites, X is a halide and B is a small metal cation.
Organic-inorganic: These compounds are typically metal halide compounds with an additional organic cation.
Among these three platforms, metal halides have seen significant progress in recent years, and they bear the most promise for broad commercialization. All these material platforms are solution-processable, so some basic chemical processes can be used to modify the important material properties in perovskite devices.
LEDs vs. Solar Cells and Photodetectors
The major difference between the material stack used in LEDs vs. solar cells and photodetectors is primarily in the role of the perovskite layer. In a solar cell or photodetector, the perovskite is normally used as an absorber, and the absorber layer is sandwiched between p-type and n-type materials to provide hole and electron transport, respectively. An external readout circuit and applied bias are used to set the device into the photoconductive mode (photodetector, linear response) or photovoltaic mode (solar cell, nonlinear response). A typical circuit connection for a solar cell or photodetector is shown below.
An example structure for a perovskite photodiode
In a perovskite LED, the device structure is similar to what is used in an OLED. These devices use a perovskite thin film as a recombination layer. Electrons and holes are injected into the perovskite layer under an applied bias, where they undergo radiative recombination and emit a photon. The structure and driver circuit connection for a perovskite light emitting diode is shown below.
An example structure for a perovskite light emitting diode
From this example, we can see that the structures are very simple, involving a perovskite thin film sandwiched between transport layers for carrier injection (for LEDs) or extraction (for photodetectors). The difference comes in the type and arrangement of transport layers used in the structure and their relative bandgaps.
Continuing Innovation in Perovskite Light Emitting Diodes
Continued progress in perovskite light emitting diodes and other optoelectronic devices should be focused in several areas:
Device reliability and stability: Perovskites generally degrade over time, particularly organic-inorganic perovskites, as they are sensitive to the external environment. Innovations in packaging technology may solve these problems.
Increased efficiency: This has remained a challenge since perovskites were first adapted for use in solar cells. Over the last 5 years, external quantum efficiencies have increased from 3% to over 20%, as was recently reported in Nature Reviews: Materials. This is partially a fabrication problem, as perovskite thin films must be defect-free to ensure high efficiency.
Greater understanding of tunability: This area has seen significant investigation in recent years and has been aided by density functional theory (DFT) simulations in general-purpose field solvers.
In addition, integration of perovskite light emitting diodes into traditional electronics is necessary for broad commercialization. Fortunately, this does not require special circuitry to achieve. Instead, integration is a board design problem that will be solved with the best ECAD software and PCB layout tools. For thermal considerations in high-power perovskite light emitting diodes, systems designers need a 3D field solver suite for CFD simulations to examine heat flow in the system.
If you want to integrate unique devices like perovskite light emitting diodes into your electronics, you’ll need PCB design and analysis software to build these systems and evaluate their functionality. Cadence provides powerful software that helps automate many important tasks in systems analysis, including a suite of pre-layout and post-layout simulation features to evaluate your system.
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