The biggest technical problem for OLEDs was
the limited lifetime of the organic materials. [56] In
particular, blue OLEDs historically have had a lifetime of
around 14,000 hours to half original brightness (five years
at 8 hours a day) when used for flat- panel displays. This
is lower than the typical lifetime of LCD , LED or PDP
technology— each currently rated for about 25, 000 –
40, 000 hours to half brightness, depending on
manufacturer and model. [57][58] However, some
manufacturers' displays aim to increase the lifespan of
OLED displays, pushing their expected life past that of
LCD displays by improving light outcoupling, thus
achieving the same brightness at a lower drive current.
[59][60] In 2007, experimental OLEDs were created which
can sustain 400 cd/m 2 of luminance for over 198, 000
hours for green OLEDs and 62, 000 hours for blue OLEDs.
[61]
Color balance issues: Additionally, as the OLED material
used to produce blue light degrades significantly more
rapidly than the materials that produce other colors, blue
light output will decrease relative to the other colors of
light. This differential color output change will change the
color balance of the display and is much more noticeable
than a decrease in overall luminance. [62] This can be
partially avoided by adjusting colour balance but this may
require advanced control circuits and interaction with the
user, which is unacceptable for some users. In order to
delay the problem, manufacturers bias the colour balance
towards blue so that the display initially has an artificially
blue tint, leading to complaints of artificial- looking, over-
saturated colors. More commonly, though , manufacturers
optimize the size of the R, G and B subpixels to reduce
the current density through the subpixel in order to
equalize lifetime at full luminance. For example, a blue
subpixel may be 100% larger than the green subpixel.
The red subpixel may be 10% smaller than the green .
Efficiency of blue OLEDs: Improvements to the
efficiency and lifetime of blue OLEDs is vital to the success of OLEDs as replacements for LCD technology.
Considerable research has been invested in developing
blue OLEDs with high external quantum efficiency as well
as a deeper blue color. [63][64] External quantum
efficiency values of 20% and 19% have been reported for
red (625 nm) and green (530 nm) diodes, respectively.
[65][66] However, blue diodes (430 nm) have only been
able to achieve maximum external quantum efficiencies
in the range of 4% to 6%. [67]