Organic semiconductors with bipolar charge transporting character are promising for optoelectronic applications, but the molecular design strategies of bipolar materials mostly rely on donor-acceptor systems, requiring both donor and acceptor...

Highly efficient blue electroluminescent devices were realized by using a solution-processable wholly-aromatic bipolar host material prepared through an insulating C(sp3) bridge linking strategy.

Trap-assisted recombination loss in the cathode buffer layers (CBLs) is detrimental to the electron extraction process and severely restricts the power conversion efficiencies (PCEs) of organic solar cells (OSCs). Herein, a novel organic-inorganic hybrid film composed of zinc oxide (ZnO) and 2,3,5,6-tetrafluoro-7,7,8, 8-tetracyanoquinodimethane (F4TCNQ) is designed to fill the intrinsic charge traps of ZnO-based CBLs by doping F4TCNQ for high-performance inverted OSCs. Thus, constructed ZnO:F4TCNQ hybrid film exhibits enhanced surface hydrophobicity and adjustable energy levels, providing favorable interfacial condition for electron extraction process. Consequently, trap-assisted recombination loss in the CBLs was efficiently suppressed, leading to the significantly improved fill factor and PCEs of both fullerene-and non-fullerene-based OSCs using the ZnO:F4TCNQ hybrid CBLs. This work illustrates a convenient organic acceptor doping approach to suppress the internal charge traps of traditional inorganic CBLs, which will shed new light on the fabrication of high-performance CBLs with facile electron extraction processes in inverted OSC devices.

Organic light-emitting diodes (OLEDs) with ultrathin emissive layers (EMLs) have attracted much attention recently due to their great potential in the solid-state lighting and flat panel display areas. Here, phosphorescent, fluorescent, and thermally activated delayed fluorescent (TADF) ultrathin OLEDs were developed and investigated to reveal their exact mechanisms in energy transfer for exciton sensitization. It was found that the formation of an interface exciplex is crucial for realizing high-performance ultrathin OLEDs, and the energy transfer from exciplexes to phosphorescent molecules is the most efficient among three kinds of electroluminescent devices. Moreover, the synergistic sensitization using both interface exciplex and phosphor can significantly improve the performance of ultrathin fluorescent OLEDs by the efficient Forster resonance energy transfer (FRET) through multiple channels from the exciplexes and/or phosphors to fluorescent molecules. By employing the phosphor-assisted interface exciplex sensitization strategy, the green ultrathin fluorescent OLEDs reach a high external quantum efficiency (EQE) of up to 8.1%, which is by far the first report on ultrathin fluorescent OLEDs with EQE exceeding 5%. These results demonstrate the fundamental advance of exciton manipulation in improving the device performance of ultrathin OLEDs with the newly proposed synergistic sensitization strategy, shedding light on the development of highly efficient ultrathin fluorescent devices.