This is Science: Elastic Quantum Dot Display

    In microelectronics, there has been a noticeable bias or, if you like, a trend towards various flexible solutions that do not require substrates made of glass or silicon (for example, flexible electronics based on polysilicon ). So displays were no exception , even such exotic ones as quantum dot displays.

    So, what is this wonderful object such a quantum dot? If we take a piece of a semiconductor (silicon or cadmium sulfide, for example) and begin to crush it in the dark under a purple lamp, then at some point we will see luminescence. In this case, the smaller the particle size of the semiconductor or quantum dot, the shorter the luminescence wavelength we can observe (shift to the blue region of the spectrum). This phenomenon is explained by an increase in the band gap of the semiconductor with a decrease in the size of the nanoparticle. A similar phenomenon will be observed if we connect a quantum dot to the battery, and it is called electroluminescence . The backlight of your watch most likely works on this effect.

    The forbidden zone of a semiconductor or the diameter of a nanoparticle and the color of the solution of the core-shell nanoparticles, as well as the spectrum of materials for making quantum dots with desired optical properties. A source

    Thus, in order to get red, green or blue colors, we do not need to develop new materials and technologies for their application, as, for example, it was with OLED displays. Instead, we can synthesize 3 different solutions and simply mix them to get a given color or use individually to create display pixels. Accordingly, scientists from the very opening of quantum dots at the dawn of the 90s began to think about using them in displays, especially after the successful implementation of LCD matrices.

    However, it was not so simple to carry out the plan, and right up to the start of the zero real prototype of working pixels or the whole display simply did not exist. Just a couple of years ago in 2011, Samsung, interested in new types of displays, conducted a series of surveys, which allowed us to create a full QLED ( quantum dots light emitting diode ) display.

    In a recent paper published in the journal ACSNano , a group of scientists from Singapore and Turkey presented the concept of a very flexible quantum dot display, which - who knows - maybe in a couple of years will be announced with the new Samsung 7, for example.

    The main problems in creating such displays: a limited range of suitable materials and poor mechanical resistance to bending and twisting. However, using polyimide Kapton , it allows us to solve part of the problems, to optimize the process and get the output is quite large (square millimeters) QLED the brightness of 20,000 cd / m 2 , which is by far a record in the field of flexible diodes with quantum dots.

    (a) Scheme of the developed QLED (layers from top to bottom: Kapton polymer film / Al / ZnO nanoparticles / CdSe-CdS-ZnS quantum dots / TCTA / MoO 3 / Ag polymer ), (b) AFM image of the obtained film, (c) electronic level diagram and (d) working QLED

    The mechanical properties of the resulting device are so good that it can be used as a sticker, gluing and peeling several times, as well as bending in various directions (the brightness in relative units does not decrease significantly, no more than 5%). With respect to optical characteristics, the diodes made withstood the test, demonstrating a maximum brightness of 20,000 cd / m 2 at an external quantum efficiency of 4%.

    (a) Normalized electroluminescence spectra for the fabricated diodes, (b) the coverage of the RGB spectrum in CIE coordinates (for comparison, similar coverage for the HDTV standard is given), (c) the brightness and (d) the external quantum output of the diodes

    And in conclusion, I will give an example of the operation diodes in real, so to speak, field conditions:

    Demonstration of QLED on flat (ad) and curved surfaces (ef)

    Original article in ACSNano (DOI: 10.1021 / nn502588k)

    PS: LeoMat suggested that Apple filed 3 patents for QLED displays at the very end of 2013.

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