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

Abstract

The open-circuit voltage (Voc) dependency on hole-extraction layers (HELs) with different energy levels and mobility was investigated in a single stack heterojunction subphthalocyanine chloride (SubPc)/C60 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 Voc in SubPc/C60 device due to a corresponding built-in potential increase. The high mobility of HELs can also increase Voc with increasing Jsc 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 Voc (from 0.90 to 1.15 V) with an improvement in efficiency compared to a reference SubPc/C60 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.