Improvement in the open-circuit voltage of an organic photovoltaic device through selection of a suitable and low-lying highest occupied molecular orbital for the electron donor layer

A high open-circuit voltage (VOC) of an organic photovoltaic device (OPV) has been realized using an ultrathin electron donor layer, 2,3-Bis(2-(diphenylamino)-9,9′- spirobifluorene-7-yl)fumaronitrile (PhSPFN), which exhibits the most suitable and low-lying highest occupied molecular orbital (HOMO) to align between the anode and donor energy levels. The planar heterojunction OPV, represented as indium tin oxide electrode/PhSPFN/fullerene C60/bathocuproine/aluminum electrode shows high performance with aVOCof 0.91 V, short current density of 3.9 mA/cm2, fill factor of 56% and power conversion efficiency of 2% under an air-mass of 1.5 global illumination at 1 sun. In addition, the effect of theVOCchange is discussed in terms of various donor materials. TheVOCturns out to be restricted to the energetic alignment between the work function of the anode and the HOMO level, indicating that the optimization ofVOCrequires energetically good contact between the anode and organic materials.