Elucidation of hierarchical metallophthalocyanine buffer layers in bulk heterojunction solar cells

Vapour deposited metallophthalocyanines (VoPC, NiPC, SnPC, TiPC, FePC, InPC) were inserted as thin p-type buffer layers into organic solar cells consisting of regio-regular poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester in order to modify the band alignment for enhanced photovoltaic responses. It is observed that the VoPC, NiPC and SnPC show higher efficiencies in both similar to 5 nm and similar to 10 nm thicknesses of film when coated on a PEDOT: PSS layer. The observations were an enhanced efficiency with a maximum J(SC) value of 14.80 mA cm(- 2), V-OC of 0.60, and FF of 51% with a conversion efficiency of 3.61% in the case of similar to 5 nm thick VoPC, while the similar to 5 nm thick NiPC shows a J(SC) value of 11.15 mA cm (-2) with 3.13% efficiency, and similarly the similar to 10 nm thick NiPC has a J(SC) value of 8.98 mA cm(-2) with overall efficiency of 2.52%. However, the TiPC, FePC and InPC show poor efficiencies even lower than those of the usual bulk-heterojunction solar cells with deposition of either a similar to 5 nm or a 10 nm buffer layer. The enhanced efficiency in VoPC, NiPC and SnPC may be the result of extended absorption, high transparency, planar porphyrin complex orientation and holding p-type properties to transfer the hole efficiently towards the anodes, with additionally a better bicontinuous interpenetrating network with vapour deposited layers, which greatly reduces the exciton loss and improves the charge transport capability.