Inkjet-Printed Aligned Quantum Rod Enhancement Films for their Application in Liquid Crystal Displays
Semiconductor quantum rods (QRs) show a polarized emission, which opens up the possibility of both brightness and color enhancement for liquid crystal displays (LCD) in the form of quantum rod enhancement films (QREF) for LCD backlights. However, the QR alignment over a large area, suitable for displays, is a challenge. Inkjet printing of QREFs introduced here, allows fabrication of well-aligned, uniform QREFs on photoaligned substrates using optimized QR inks. We observed that the ink composition and printing condition affect the QR alignment quality seriously. Relative humidity of 50% with an exposure energy of 1 J/cm2 for the photoalignment process provided optimal conditions for QREFs. We have successfully shown a good QR alignment for the 2.5-inch films and able to align QR in multiple layers. Thus fabricated QREF show polarization ratio of 7.2:1. These QREFs were combined with blue LED and deployed as a backlight unit for LCD that shows ~250 nits of brightness with an optical efficiency of ~8%, reaching 109% of NTSC in a CIE1976 color space. Thus, this printed QREF, over a large area, provides an unprecedented increase of 77% in the optical efficiency of the LCDs and simultaneously offer better color performance.