Handset displays come in two varieties: LCD and OLED. The former is a great deal more common and remains far easier to produce. In fact, the only brand to delve extensively into OLED technology is Samsung, and even they only feature it on select models. That said, OLED is arguably the wave of the future. Below, we'll look at these two major variants, how they work, and what sets them apart:
LCD: The LCD (or Liquid Crystal Display) designation covers a broad spectrum of technologies, ranging from the ho-hum monochrome displays found on old digital clocks, to the hypnotizing fantasias of color and light utilized on certain HDTVs. Of course, those found in handsets err toward the latter—in fact, they’re some of the most sophisticated you’ll find anywhere—but the key mechanical principles are the same across all LCDs.
LCD displays do literally utilize Liquid Crystals, as far-fetched as that may sound. What, exactly, is a liquid crystal, if not something left in the wake of a unicorn? Liquid crystals exist in the strange space between solids and liquids: like solids, their molecules are more or less stable in direction; but like liquids, they can change relative position. They’re also easily affected by electrical current.
LCD display are made by sandwiching liquid crystals between polarized sheets of glass, electrodes, and other elements, and passing light and electricity through those various layers. Suffice it to say that the liquid crystals then respond and reorient, and in turn redirect the light.
TFT (Thin Film Transistor): You may very well have encountered the TFT acronym in your perusal of LCD display-sporting handsets. Fear not: all complex LCDs—meaning, not the kind featured in alarm clocks and cheap calculators—feature a Thin Film Transistor. For those wondering how a screen knows which pixels to illuminate, you’ve stumbled upon (part of) the answer: TFTs effectively serve to direct commands to a screen’s many pixels. Rather than addressing each pixel individually, the grid is divided into rows and columns. Rows are turned on and off individually, and charges are sent down a designated column. So only the correct area—the active row in the charged column—receives a charge and emits light. The precise degree of charge determines the extent to which electrons in the liquid crystal are turned, and thus the relative brightness of the pixel.
TFTs are also utilized in OLED screens, but are instead indicated by AM (as in AMOLED), short for Active Matrix.
IPS (In-Plane Switching): Virtually all complex LCD displays are IPS-LCDs. IPS stands for In-Plane Switching, an advancement developed to counter problems with response speed and viewing angles in earlier LCDs. Essentially, IPS keeps liquid crystals in a plane parallel with the LCD panel (hence the name ‘in-plane’), so the image is minimally compromised by changes in perspective.
OLED (Organic Light-Emitting Diodes): OLEDs arguably surpass LCDs in a number of important aspects, and may very well represent the future of mobile display technology. Indeed, theoretical applications—including massive, ultra-thin HD displays that can be rolled up and stowed in a drawer, screens built into clothing, and heads-up displays in cars—are the stuff of future-fantasies from years past.
Like LCDs, OLEDs are constructed by layering various panels and substrates—but that’s about where the similarities end. Bear with us here, because this next part is hard to simplify: OLEDs utilize two organic substrates that, depending on the exact compounds used (polyaniline and polyfluorene are common inclusions), conduct and emit light. Below the organic polymers is a cathode (which contributes electrons when hit with a current), and atop it is an anode (which removes electrons). At the very top is, of course, the glass substrate—which, in the case of the smartphone, is a digitizer. Effectively, the shuffling of electrons in the emissive organic layer creates “holes” that are then re-filled by new electrons, which release their energy in the form of light. Any questions? (We certainly hope not.)
What makes OLEDs special? Well, for one thing, they’re extremely flexible in shape. Theoretically, an OLED television could one day be rolled up and tucked in backpack or drawer. They also don’t require backlighting, like a traditional LCD would, which means, generally, that they use less power. Similarly, the absence of backlighting means that black pixels simply aren’t lit, so they’re truly black. This translates to enhanced contrast—a particularly appreciable improvement in the context of reading on a small device. Broadly speaking, OLEDs are capable of wider viewing angles, faster screen refreshing, and more accurate color reproduction. And because OLEDs are a relatively young form of technology (LCDs have been around in basic form since the 1970s), there is, theoretically, a great deal more room for advancement within the platform.