TL;DR: below is described how an IPS screen is built. Few screen parts could make an impact on one of the problems, discussed here, based on limited evidence. These parts are:
- front polarizer
- LCD matrix itself, presumably glass substrate with transistors
- BEF and similar brightness enhancing layers for a backlight
This post will be updated when I find mistakes or when more data appears.
IPS screen parts (and a little bit about OLED)
What is inside an IPS screen
Click here to see llustration
This is how an IPS screen works. The light from a backlight passes through a rear polarizer, which allows light to pass through only in a certain “plane”. The light then hits the liquid crystals. Passing through them, the light can change its "plane". At the exit, the light comes out through the front polarizer, and it also transmits light with a certain "plane". Liquid crystals can stop the light or redirect light from the lower polarizer so it can pass through the upper polarizer.
(By "plane" I mean a simplified reference to polarization, you can learn more about polarization here
In IPS matrices, front and rear polarizers are placed in the same direction, and the crystals transmit light through without twisting.
In TN matrices, the front polarizer is placed with an angle of 90 degrees to the lower one, and the crystals twist the polarization of the light to pass it through.
In front of the liquid crystals, there is a color filter to make colored pixels from the light, and behind the liquid crystals, there are transistors with electrodes for the liquid crystals to work.
Thus, the core of an IPS screen is a glued block of these layers: front polarizer - glass substrate with color filter - liquid crystals between the glasses - glass substrate with transistors and electrodes - rear polarizer. This is a required part of the screen.
Behind this block, a backlight is situated (for very old CCFL screens, lamps, for new LEDs) and a block of backlight layers. Backlight layers are needed so that the tiny light source (a small led strip or CCFL lamp) evenly floods the entire large screen. They direct and evenly scatter the light. Backlight is also an obligatory part of the screen.
But there is space for improvements! Manufacturers try to utilize the light from a backlight in the fullest possible way: so that not a single photon is wasted and can eventually fly into the user's eye.
First, for this, all the layers are made to mirror any light forward onto the LCD matrix, and not absorb.
Secondly, a bunch of different layers is used specifically in order to use light very efficiently, increasing screen brightness and increasing energy efficiency. The largest manufacturer of these layers (3M) calls them brightness enhancement films. This is an optional part of the screen. A manufacturer can choose not to use them at all, or use them in a wide variety of configurations.
Thirdly, anti-reflective coatings are used inside the screen, so that external light does not interfere with seeing the image.
All modern flat LCD screens of laptops, monitors, telephones are arranged in the same way, with the exception of tiny differences in the matrix (for example, electrodes can be on both sides of liquid crystals).
Where to learn more about layers:
Nice presentation about LCD layers that explains their qualities
Where to learn more about how an LCD works:
Detailed article about polarizaton
Article about IPS and TN in simple language
Article about the main difference between TN, IPS and VA
Video that schematically shows how TN liquid crystals 'rotate' light
Brightness enhancement films
They have been used for a long time. By itself, the presence of any layer within the screen does not guarantee that it will be problematic.
The main manufacturer of films is 3M, but they are also produced by a long list of manufacturers.
Below are both layer names and their respective marketing names from 3M.
Each of the listed films has a number of versions / modifications / parameters: for example, among DBEF films there is a specific film called DBEF-D550.
Prism film. Its task is to direct all the light forward into the eyes, and not let it scatter to the sides. Anything that can be scattered to the sides will be reflected back down. 3M sells it under the name Brightness Enhancement Film (BEF). Often used in combination of two BEF at 90 degrees to each other.
Multi-Functional Prism Sheet. Combines a film-prism and a diffuser.
Reflective polarizer. Its task is to transmit forward only polarized light and reflect unpolarized light back. The rear polarizer cannot do this; it absorbs unpolarized light uneconomically. A reflective polarizer allows unpolarized light to be returned back and reflected from the lower layers of the illumination endlessly until it all comes out polarized upwards. Sold under the name Dual Brightness Enhancement Film (DBEF). Located next to the rear polarizer. It must be above all BEFs if used in combination with them.
It can increase the brightness by 50-60% for the same amount of light from the backlight.
Brightness Enhancement Film Reflective Polarizer (BEFRP) is a combination of a reflective polarizer and a brightness-enhancing film in one film. BEFRP is often used in combination with BEF.
Collimating Multi-layer Optical Film (CMOF) is a multifunctional multilayer film, a combination of a collimating film and a reflective polarizer.
This list may not be complete - films can be molded together, enhanced, and merged.
Many films are made like a Fresnel lens - a flat lens that refracts light purely due to its texture.
In projection TVs, there is a layer called the fresnel lens, which is visually similar, but used for different purposes and refracts the rays differently from the BEF.
Improvements are going further, and sooner or later we will see new films, for example Quantum Dot Film.
Where to learn more about films:
Big article about films, with configuration samples (written in 2010)
Article that describes the films and also has a list of manufacturers
(PDF) Part of a book Applied Prismatic and Reflective Optics that provides a lot of details about these films
Brief description at 3M website
(PDF) Brief specifications, BEF III
(PDF) Brief specifications, DBEF
(PDF) Brief specifications, DBEF II
(PDF) Brief specifications, different films
Wikipedia article about LCD Screens: Illumination
Where to look at the films:
Video that demonstrates how single BEF and two BEF layers work, using a laser
Video where a person has a layer that looks very much like BEF
Video where iPhone is disassembled and two prism films are seen
A bit about OLED
Amoled and other similar OLED screens do not have so many layers as IPS (or any other liquid crystal screen). OLED screens are made up of tiny LEDs so they don't need a backlight.
Strictly speaking, OLED matrix is not a number of separate tiny diodes, but a combination of layers that, when added on top of each other, form a matrix of tiny diodes.
On top of the OLED matrix, there is a front polarizer, which is used for other purposes than on IPS.
How OLED screens achieve the same "improvement" that hurts the eyes on IPS is not yet clear - but they definitely can do the same effect by some other means.
Video where flexible amoled is disassembled under a microscope
Safety precautions when disassembling an IPS-matrix
Please note that everything below is not a piece of professional advice and just a random post from the Internet. Use your good judgment and be careful.
There are two dangers in the LCD matrix when disassembling.
1. Liquid crystals. They are located between two glasses inside the matrix. The glasses are tightly attached to each other. If you do not break the matrix purposefully, do not bend it until it cracks, then the liquid crystals will stay inside, completely safe. If the matrix is broken (which I did with six screens to get to the transistor layer), the liquid crystals will be visible and will smear. They are not very fluid, most of them will remain on the glass.
For liquid crystals, MAAB is often used. Description of the substance
This is a hazard class 3 substance (skin / eye contact - 2). Those who have used pesticides for home or garden plants can imagine these markings. MAAB is insoluble in water. Not particularly volatile. It's hard to breathe it in. The main thing is not to burn it, then it will evaporate. Do not eat it (do not lick your fingers), do not allow it to get into the eyes. Apart from ingestion, its main danger is to irritate the skin / eyes.
There is so little MAAB in the telephone matrix that it is impossible to get poisoned.
My personal experience: I broke all 6 matrices, and didn't erase liquid crystals right away. I smeared my fingers, nothing happened to the skin. Matrices with crystals were in the room, loosely wrapped, and nothing happened.
Despite the fact that the substance is described as non-volatile, it still evaporates slightly. For a week I felt the traces of a substance through unpleasant bitterness on my lips, it was evaporating from somewhere where I smeared it.
There were no symptoms of poisoning, even the smallest, for the entire time.
I suppose that it is best to get rid of MAAB at the very beginning, carefully erasing it and throwing it away where children / puppies / kittens cannot find it.
Other similar substances could theoretically be used instead of MAAB.
[Display Engineer Response about the Safety of a Broken LCD (Quora)](https://www.quora.com/Is-it-safe-to-take-apart-an-LCD-monitor-to-create-something-I-hear-the-liquid-crystal-inside- can-be-dangerous-so-if-I-wear-gloves-a-mask-and-work-outdoors-will-it-be-safe)
2. Glass substrate. This is not glass like window glass, it easily crumbles into tiny glass dust. They can scratch your fingers, so it is best to wear gloves during disassembly.
Considering points 1 and 2, when disassembling, it is advisable to expel kittens, puppies, children from the premises.
If you have is a desire to disassemble a very ancient screen on CCFL, be extremely careful with the lamps. There is a highly toxic substance (mercury) inside them, so avoid breaking lamps by all means.
Books to read
You can read all these books in Perlego library. It has two weeks free trial.
Books about IPS and LCD:
Introduction to Flat Panel Displays - many technical details about LCD and OLED (but no data on backlight layers)
LED Backlights - has a small chapter about Lens Films and Reflective Polarization Films
Flat Panel Display Manufacturing
Modeling and Optimization of LCD Optical Performance - a highly complicated one
Books about OLED:
OLED Display Fundamentals and Applications
Where to look at the real disassembled screen:
Video - Amazing Layers Of Smartphone Screen || IPS LCD Screen Teardown