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The exciplex forming co-host with phosphorescent dopant system has potential to realize highly efficient phosphorescent organic light emitting didoes (PhOLEDs). However, the exciplex forming co-host for blue phosphorescent OLEDs has been rarely introduced because of higher triplet level of the blue dopant than green and red dopants. In this work, a novel exciplex forming co-host with high triplet energy level is developed by mixing a phosphine oxide based electron transporting material, PO-T2T, and a hole transporting material, N, N′-dicarbazolyl-3,5-benzene (mCP). Photo-physical analysis shows that the exciplexes are formed efficiently in the host and the energy transfer from the exciplex to blue phosphorescent dopant (iridium(III)bis[(4,6-difluorophenyl)-pyridinato- N,C2′]picolinate; FIrpic) is also efficient, enabling the triplet harvest without energy loss. As a result, an unprecedented high performance blue PhOLED with the exciplex forming co-host is demonstrated, showing a maximum external quantum efficiency (EQE) of 30.3%, a maximum power efficiency of 66 lm W−1, and low driving voltage of 2.75 at 100 cd m−2, 3.29 V at 1000 cd m−2, and 4.65 V at 10 000 cd m−2, respectively. The importance of the exciton confinement in the exciplex forming co-host is further investigated which is directly related to the performance of PhOLEDs. [ABSTRACT FROM AUTHOR]

Phosphorescent organic light-emitting diodes (OLEDs) with ultimate efficiency in terms of the external quantum efficiency (EQE), driving voltage, and efficiency roll-off are reported, making use of an exciplex-forming co-host. This exciplex-forming co-host system enables efficient singlet and triplet energy transfers from the host exciplex to the phosphorescent dopant because the singlet and triplet energies of the exciplex are almost identical. In addition, the system has low probability of direct trapping of charges at the dopant molecules and no charge-injection barrier from the charge-transport layers to the emitting layer. By combining all these factors, the OLEDs achieve a low turn-on voltage of 2.4 V, a very high EQE of 29.1% and a very high power efficiency of 124 lm W−1. In addition, the OLEDs achieve an extremely low efficiency roll-off. The EQE of the optimized OLED is maintained at more than 27.8%, up to 10 000 cd m−2. [ABSTRACT FROM AUTHOR]

In article number 1700702, Sang‐Woo Kim and co‐workers report high‐performance piezoelectric, pyroelectric, and triboelectric nanogenerators based on P(VDF‐TrFE) with controlled crystallinity and dipole alignment. A high‐dipole‐moment solvent enhances the end‐to‐end chain length and chain orientation, and leads to higher crystallinity and better dipole alignment of P(VDF‐TrFE). [ABSTRACT FROM AUTHOR]

On page 4914, J.‐J. Kim and co‐workers use an exciplex‐forming co‐host to create phosphorescent organic light‐emitting diodes with ultimate efficiencies reported in terms of the external quantum efficiency (EQE), driving voltage, and efficiency rolloff. The image expresses the formation of an exciplex by the recombination of an electron and a hole, followed by energy transfer from the exciplex‐forming co‐host to the dopant, and the luminescence of the green light from the dopant. [ABSTRACT FROM AUTHOR]