These new materials have the potential to revolutionize advanced LED technology, including for outdoor displays, automotive lighting, wearable displays, LEDs and in home lighting. They could also serve as the basis for new blue-based LEDs.
The semiconductor, which is produced by splitting halide perovskite crystals, provides a promising means to make LED products. Current LED technologies are based on semiconductors of different materials. The best known LED is the Cree XP-G2. This light emitter has the maximum color gamut (color range) available in a light emitter (100 or 600 nm), but is limited by its output power (brightness) as well as its energy footprint. The most popular LEDs today use mercury plated phosphors to produce luminescence (light production). These light emitting diodes (LED) are not blue in color. They just turn blue based on the light they emit. Other blue-based LEDs are not available. One limitation of these light emitting diodes is their output power. While they could be used to illuminate or change lighting conditions in a home, these diodes simply cannot directly provide sufficient power to overcome the power demands of an LED bulb.
The UC Berkeley team has developed a new type of LED called halide perovskite that is produced via the direct coupling of two halide atoms in a boron fluoride (Bf) compound. Bf, a semiconductor, is an extremely common compound in many semiconductor materials. The process to produce halide perovskite is as simple as replacing one of the halides with boron. Halide or boron crystals in a compound are the best performing materials. Boron fluoride is readily available and cheap, which makes it an attractive source for synthesis. One of the main drawbacks of perovskite-based light emitting diode is the short lifetime of the material, but the UC Berkeley researchers have developed an elegant way around the issue by exploiting two unique characteristics of halide perovskite.
First, the team used the boron fluoride (Bf) compound to bind to a halide atom (in this case halide perovskite, also known as bismuth borate) in halide perovskite. In this way, the light emitting source could be coupled with the halide perovskite. Since both the emission and output power of halide perovskite is very low, the output power of the LED can be made significantly larger with very low cost. The material is also extremely sensitive to how far it is embedded in material, and other materials can interfere with its emitted light.
The use of boron fluoride (Bf) compounds in LEDs is becoming popular again, because of its unique properties. For example, because bismuth borate is the best light emitting material in the world (as long as you use high purity halide perovskite, which is expensive to make and is usually produced in extremely high purity boron fluoride), boron fluoride appears to be the perfect compound for LEDs (it absorbs blue light easily, and provides the best performance for light emitters of all colors). These properties (among many) make it an ideal candidate for LED applications.
The second unique property of halide perovskite is that it can be made either at room temperature or at 10 degrees C. The UC Berkeley team found that their new halide perovskite could produce a temperature effect at room temperature if they used the bismuth perovskite (Bf) compound as the source of boron. If the boron fluoride were used, the output power of the material would also be affected when it was heated as it would make the material produce less luminescence. This heat dependent process was a new feature of this new material, and was not previously possible.
The production of halide perovskite offers many important advantages, and it will be interesting to see if Halide Perovskite can be employed in products and in many different applications.