On the problem of open circuit voltage in metal phthalocyanine/C60 organic solar cells

Abstract

The open circuit voltage (VOC) plays a crucial role in determining the efficiency of organic solar cells. Models ofthe VOC based on (i) the energy difference between the LUMO of the acceptor material and the HOMO of the donor material at the heterointerface and (ii) chemical potential gradient which depends on the carrier mobility in a bilayer cell, areinadequate to understand the exact origin of the VOC. In this review article, the VOC in various planar and non-planar metal phthalocyanine/C60 solar cells are analyzed. These results are compared in CuPc/C60 and SubPc/C60 solar cells as a representative case of the planar and non-planar metal phthalocyanine/C60 solar cells, respectively. Regardless of unfavorable characteristics of SubPc films, the VOC value of 0.92 to 0.98V in SubPc (13 nm)/C60 (33 - 32.5 nm) compared to 0.44 to 0.49V in CuPc (20 - 40 nm)/C60 (40 - 30 nm) solar cells was noticed. It is suggested that the structure, morphology, and absorption properties of the evaporated film of the donor materials and the efficient separation of charges at the donor/acceptor interface in bilayer planar and non-planar metal phthalocyanine/C60 solar cells are also imperative in determining the VOC. © 2011 VBRI press.