Display technology: from LCD to QLED

Display technology: from LCD to QLED The purpose of this thesis is to show the characteristics and validity of LCD Technology by reconstructing the diachronic process that brought the production systems from primitive and cathodic TV to the latest Led Technology, passing from the “traditional” LCD market. The work is divided into three chapters, respectively, of LCD technology, OLED technology, and QLED technology. The starting point was 1907 when Boris Rosing, a lecturer at the technical institute in St. Petersburg, demonstrated a primitive TV system that employed the cathode ray tube, or CRT (Cathode Ray Tube) accompanied by electromagnetic deflection. The main problem for the cathode ray tube was to obtain a “vacuum” pushed inside the tube itself. The technology capable of creating this vacuum in the tube had not yet reached good levels and, at the same time, the closure and sealing systems of the kinescope were not exceptional. Even these technical issues, starting from 1950’s the picture tubes improved considerably. While liquid crystal was discovered already in 1888 by an Austrian botanist, Frederich Rheinizer, the use for advanced technologies began only later when it was soon recognized for its countless qualities. In the mid-1960s, scientists discovered that liquid crystals stimulated by external electrical charges were able to change the properties of the light that passed through the crystals. The first prototypes appeared in the late 1960 were still too unstable for mass production at least when a British researcher presented biphenyl, a truly stable liquid crystal material. The main part of the thesis is about precisely the use of nanocrystals in the lighting system represent an important renewal of LCD Technology, which soon will have to fight the advance of LED, the display system that promises to worthily replace the now defunct plasma. Today’s LCD displays, especially those for TVs, have a very high brightness, which if on the one hand makes them clearly visible even in strong light, on the other hand it can even be annoying for viewing in a dark or semi-dark environment. LCD panels dominate the mass market for electronic products, but they still have limitations that have dragged on since their birth: high black level, low contrast, sub optimal color rendering. Over time, LED backlighting technology has been developed, a recent technique allows the so-called “local dimming”, a function that acts dynamically on the various portions of the backlight, optimizing them based on each single frame being reproduced, thus significantly improving the contrast. Since then, for marketing reasons, the correct term “LCD screen with LED backlight” has sometimes been abbreviated to “LED screen” but it is improper because the LEDs present have the sole purpose of backlighting. The last chapters are about QD-led or Qled. The idea of using quantum dots as direct sources of light emerged in the 90s of the last century, when researchers highlighted the efficiency of nanocrystals in the process of converting electricity to light. The structure of a QD-led panel is like that of an Oled one, with the quantum dots divided into cells and enclosed between two conductive layers, which carry the electrical charges. The electrons and holes recombine within the nanocrystals, forming excitons that in turn cause the emission of photons with wavelengths proportional to the size of the quantum dots