Open-circuit voltage dependency on hole-extraction layers in planar heterojunction organic solar cells

The open-circuit voltage (V-oc) dependency on hole-extraction layers (HELs) with different energy levels and mobility was investigated in a single stack heterojunction subphthalocyanine chloride (SubPc)/C-60 organic solar cells. The HELs having about 0.2-0.3 eV higher highest occupied molecular orbital (HOMO) level than that of a donor material can significantly enhance the V-oc in SubPc/C-60 device due to a corresponding built-in potential increase. The high mobility of HELs can also increase V-oc with increasing J(sc) according to the simple diode equation. Among all HELs we utilized, N, N, N', N'-tetra(biphenyl-4-yl)biphenyl-4,4'-diamine (TBBD) illustrates a largest increase in V-oc (from 0.90 to 1.15 V) with an improvement in efficiency compared to a reference SubPc/C-60 device without HEL. This increase is mainly attributed to easy and rapid extraction of holes by TBBD due to its proper HOMO level and high mobility. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3610962]