Bifunctional electroluminescent and photovoltaic devices using bathocuproine as electron-transporting material and an electron acceptor

Electroluminescence (EL) devices, using 4, 4′,4′′-tris (2-methylphenyl- phenylamino) triphenylamine (m-MTDATA) as hole-transporting material and bathocuproine (BCP) as an electron-transporting material, were fabricated, which emitted bright green light peaked at 520 nm instead of the emission of m-MTDATA or BCP. It was attributed to the exciplex formation and emission at the interface of m-MTDATA and BCP. EL performance was significantly enhanced by a thin mixed layer (5 nm) of m-MTDATA and BCP inserted between the two organic layers of the original m-MTDATA/BCP bilayer device. The trilayer device showed maximum luminance of 1,205 cd/m2 at 8 V. At a luminance of 100 cd/m2, the power efficiency is 1.64 cd/A. Commission International De L’Eclairoge (CIE) color coordinates of the output spectrum of the devices at 8 V are x=0.244 and y=0.464. These devices also showed photovoltaic (PV) properties, which were sensitive to UV light. The PV diode exhibits high open-circuit voltage (Voc) of 2.10 V under illumination of 365 nm UV light with 2 mW/cm2. And the short-circuit current (Isc) of 92.5×10−6 A/cm2, fill factor (FF) of 0.30 and power conversion efficiency (ηe) of 2.91% are respectively achieved. It is considered that strong exciplex emission in an EL device is a good indicator of efficient charge transfer at the organic interface, which is a basic requirement for good PV performance. Both the bilayer and trilayer devices showed EL and PV properties, suggesting their potential use as multifunction devices.