Wing Yip Lam

Highly efficient organic light-emitting diodes with a silole-based compound

Efficient light emission was obtained in a silole-based organic light-emitting diode. A high luminous current efficiency of 20 cd/A, corresponding to an external quantum efficiency of 8%, was achieved. The apparent violation of the upper theoretical limit of 5.5% for the external quantum efficiency of a singlet emitter is discussed. With a suitably designed cathode, a high power efficiency of ∼14 lm/W was obtained. A strong dependence of the power efficiency on the thickness of Alq3 layer is also observed and explained.

Aggregation and chirality

Debate on the origin of chirality has lasted for several centuries. Lots of theories in different fields have been propounded to illustrate the possible sources. However, there were no convincing proofs could be provided. In this work, through constructing the relationship between aggregation and chirality, a significant insight was brought to explain how the chirality was generated from the achiral system. Besides, aggregation-induced circular dichroism (AICD) effect was discovered in some AIEgens decorated with amino acid or sugars and aggregation-annihilated circular dichroism (AACD) effect was reported in axially chiral systems. In AICD systems, it was proved that the chirality could transfer from chiral centers to AIEgens in the aggregate state but not solution. Meanwhile, it was concluded that the right-handed helical structures corresponded to a negative Cotton effect and vice versa. For the AACD effect, further studies suggested that the annihilation was caused by the change of twist angle within the process of aggregation.