Display. Visualization - OLED displays

The first results in organic electroluminescence (EL) date back to the 1960s, with the study of anthracene molecules by Pope et al. [1] . But it wasn't until 1987 that the manufacture of an EL diode based on evaporated organic materials (small molecules) was reported, with a better luminous efficiency than its inorganic equivalent (1.5 lm/W versus 0.5 lm/W [2]). Then, in 1990, Burroughes et al. presented the first results for EL diodes based on polymers deposited from a solution [3] . This made it possible to manufacture displays that could replace or complement the devices available at the time (CRT, LCD, FED, plasma...). Since then, R&D in this area has become very active, generating substantial investment.

The reasons for using organic EL for visualization applications are as follows:

• good luminous efficiency (∼ 1 lm/W for white display with high potential for improvement);

• low control voltage (V _threshold < 3 V, operation < 10 V);

• very low response time (well suited to video display) ;

• emissive technology: power consumption depends on image content;

• grand angle de vue (lambertian show) ;

• low thickness (determined by the thickness of the substrate and the encapsulation method) and the possibility of using flexible substrates;

• potentially low-cost (devices based on simple thin films, low-temperature manufacturing process compatible with large surfaces, elimination of color filters and LCD lightboxes, etc.).

However, there are still a number of technological hurdles that need to be overcome to benefit from these advantages. These include

• lifetime (currently < 10,000 hours) and sensitivity to humidity, oxygen and temperature (need to encapsulate with a glass or metal cover and use/storage below 60 ˚C) ;

• Differential ageing of red, green and blue pixels depending on their use: strong marking likely and color degradation ;

• development of active-matrix addressing (development of suitable, low-cost poly-Si transistor arrays);

• development of adapted industrial production tools.