In addition, the organic light-emitting diode display screen can be made lighter and thinner, with a larger viewing angle, and can significantly save electricity. However, although the OLED with better technology will replace LCD such as TFT in the future, the OLED display technology still has some shortcomings, such as short life and difficult to enlarge the screen.
Each pixel of TFT liquid crystal has a semiconductor switch, and each pixel can be directly controlled by point pulse, so each node is relatively independent and can be continuously controlled, which not only improves the response speed of the display screen, but also accurately controls the display color level, so the color of TFT liquid crystal is more realistic.
TFT liquid crystal display is characterized by good brightness, high contrast, strong layering and bright colors, but it also has the disadvantages of high power consumption and high cost.
Compared with TFT screen and OLED screen, which is better?
TFT is just a kind of LCD. Organic light-emitting diodes are not mature enough to replace LCD, but they have many advantages and will probably replace LCD in the future. ?
Organic light emitting diode, that is, organic light emitting diode (OLED), is also called organic electroluminescent display (OELD). Since 2003, this display device has been widely used in MP3 players because of its light weight and power saving. However, for DC and mobile phones, which are both digital products, only engineering samples with OLED screens have been shown in some exhibitions before, and they have not yet entered the practical application stage. However, organic light-emitting diode (OLED) screen has many incomparable advantages over LCD, so it has always been favored by people in the industry.
Organic light emitting diode display technology is different from the traditional liquid crystal display mode. It does not need backlight, and uses very thin organic material coating and glass substrate. These organic materials will emit light when current passes through them. In addition, the organic light-emitting diode display screen can be made lighter and thinner, with a larger viewing angle, and can significantly save electricity. ?
At present, among the two major technical systems of organic light-emitting diodes, the low-molecular-weight organic light-emitting diode technology is mastered by Japan, and the so-called OEL of polymer PLEDLG mobile phone is this system, and the technology and patents are mastered by British technology company CDT. Compared with PLED products, colorization is still difficult. Low molecular OLEDs are easier to be colored. Not long ago, Samsung released 65,530 color OLEDs for mobile phones. ?
However, although the OLED with better technology will replace LCD such as TFT in the future, the OLED display technology still has some shortcomings, such as short life and difficult to enlarge the screen. At present, Samsung mainly uses OLEDs, such as the newly listed SCH-X339, which uses 256-color OLEDs. As for OEL, LG is mainly used in its CU8 180 8280, which we have all seen.
In order to explain the structure of organic light-emitting diodes, each organic light-emitting diode unit can be compared to a hamburger, and the luminescent material is a vegetable sandwiched in the middle. The display unit of each organic light emitting diode can generate three different colors of light under control. Like LCD, organic light emitting diodes can also be divided into active and passive types. In passive mode, cells selected by row and column addresses are lit. In active mode, there is a thin film transistor (TFT) behind the organic light-emitting diode unit, and the light-emitting unit is lit by the TFT. Active organic light-emitting diodes save electricity, but passive organic light-emitting diodes have better display performance.
The basic structure of organic light-emitting diodes is that a thin and transparent layer of indium tin oxide (ITO) with semiconductor characteristics is connected to the positive electrode of power supply, and another layer of metal cathode is wrapped into a sandwich structure. The whole structural layer includes hole transport layer (HTL), light-emitting layer (EL) and electron transport layer (ETL). When the power supply is supplied to a suitable voltage, the positive holes and negative charges in the light-emitting layer will combine to generate light, and three primary colors of red, green and blue RGB will be generated according to different formulas to form basic colors. Organic light-emitting diodes are characterized by their own light emission, unlike TFT LCD, so they have high visibility and brightness, followed by low voltage demand, high energy-saving efficiency, fast response, light weight, thin thickness, simple structure and low cost. It is considered as one of the most promising products in 2 1 century.
The light emitting principle of organic light emitting diodes is similar to that of inorganic light emitting diodes. When the element is subjected to direct current (DC; DC), and the applied voltage energy injects driving electrons and holes into the device from the cathode and anode respectively. When they meet and combine in conduction, so-called electron-hole trapping is formed. When a chemical molecule is excited by external energy, if the electron spin is paired with the ground state electron, it is a singlet state, and the light released by it is the so-called fluorescence; On the other hand, if the spins of excited electrons and ground electrons are unpaired and parallel, it is called triplet state, and the light released by it is called phosphorescence.
When the state of an electron returns from the excited high energy level to the steady low energy level, its energy will be released in the form of luminescence or heat dissipation, and some photons can be used as display functions; However, triplet phosphorescence cannot be observed in organic fluorescent materials at room temperature, so the theoretical limit of luminous efficiency of PM- organic light-emitting diode devices is only 25%.
The light-emitting principle of PM- organic light-emitting diodes is to convert the released energy into photons by using the energy level difference of materials, so we can choose suitable materials as the light-emitting layer or dope dyes in the light-emitting layer to obtain the light-emitting color we need. In addition, the binding reaction between electrons and holes is usually within tens of nanoseconds (ns), so the response speed of PM- OLED is very fast.
Typical structure of PM-OLEM. A typical PM- organic light emitting diode consists of a glass substrate ITO (indium tin oxide; ; Indium tin oxide) anode, emitting material layer and cathode, etc. In which a thin and transparent ITO anode and a metal cathode sandwich an organic light-emitting layer, and when holes injected into the anode by voltage are combined with electrons from the cathode, the organic material is excited to emit light.
At present, the multi-layer PM- organic light-emitting diode structure with good luminous efficiency and wide application needs to make hole injection layer (hole injection layer; HIL), hole transport layer (hole transport layer; HTL), electron transport layer (electron transport layer; ETL) and an electron injection layer (electron injection layer; EIL), and it is necessary to set an insulating layer between each transport layer and the electrode, so the processing difficulty of thermal evaporation is relatively high and the manufacturing process becomes complicated.
Because organic materials and metals are quite sensitive to oxygen and water vapor, they need to be packaged and protected after production. Although PM- OLED needs to be composed of several layers of organic thin films, the thickness of organic thin films is only about 1 0,000 ~1500 A (0. 10 ~ 0. 15 um), and the total thickness of the whole display panel after packaging and adding desiccant is less than 200.