Research On Enhanced Performance In Microstructured Organic Light-emitting Devices And Organic Solar Cells

Organic light-emitting devices (OLEDs) have been attracting great attentiondue to their advantages in light weight, low cost, low power consumption,abundant materials. At present, OLEDs have been used into a mobile phone and afew other electronic products. However, it can not achieve a large scale application.There are a few questions to be solved, such as viewing-angle dependencecharacteristics of top-emitting organic light-emitting diodes(TOLEDs) and lowpower conversion efficiency in organic solar cells (OSCs). In this thesis, muchresearch has been done on viewing-angle dependence characteristics of TOLEDsand power conversion efficiency in OSCs. The microstructures have been fabricatedand applied in TOLEDs to eliminate the angular dependence emission of TOLEDs. Atthe same time, the microstructures have also been applied in OSCs to improve thepower conversion efficiency. Moreover, we have also fabricated TOLEDs on a curvedsurface to achieve omnidirectional light emission. The results include the followingaspects:(1) An effective way has been demonstrated that resolve viewing-anglecharacteristics and narrow spectra owing to microcavity effect in red and blueemission TOLEDs by introducing periodic microstructures. From this approach,periodically changed cavity length can be achieved and the range of the resonantwavelength in these devices can be broadened. As a result, TOLEDs with microstructures exhibit a quasi-Lambertian emission pattern and have no color shiftat different viewing angles. In addition, we can almost observe the uniformluminance and efficiency in TOLEDs with and without microstructures.(2) We have fabricated a TOLED on curved surface using a photopolymer lensas substrate and demonstrated that omnidirectional emission from TOLEDs on acurved surface. Compared to the planar TOLEDs, the emission intensities ofTOLEDs on curved surface show an obviously slower decrease with the increasingof the observation angle and can be observed at90°off the surface normal. Thisapproach is a new alternative and important for the applications of TOLEDs insolid-state light.(3) A periodic corrugation was introduced into the device structure, which leadsto an enhanced light absorption in the OSCs by elongating the optical path of theincident light inside the absorber material. Moreover, the indium-tin-oxide-free OSCshave been fabricated using a semitransparent Au film as anode. A comparative studybetween the OSCs with different metal cathodes shows that formation of an idealohmic contact at low-workfunction Ca and the organic interface reduces seriesresistance and increases the carrier collection. The highest power conversionefficiency of optimal OSC with a corrugated Au anode and Ca/Ag cathode is1.4%,which is significantly improved in contrast to0.61%for the OSC with a planar Alcathode. Because of the shortage of indium, the indium–tin-oxide-free OSCs havebeen fabricated using Au film as anode and a periodic corrugation was introduced intothe device structure, which leads to a low cost and an enhanced power conversion efficiency in the OSCs.