Ni-etioporphyrin-III: Solid-state properties and photovoltaic performance

Nickel complexes with porphyrin-type ligands are the second most abundant in crude oil after vanadium complexes; in certain fossils, their relative concentration may be even higher. In this work, nickel(II) etioporphyrin-III, Ni-EtioP-III, a member of the etio-type family of oil porphyrins, was synthesized and investigated with a particular interest in its solid-state properties. A single-crystal X-ray analysis determined the molecular and crystal structure of Ni-EtioP-III. The electronic absorption spectra, morphology and photoelectrical parameters of vacuum-sublimed Ni-EtioP-III films were compared to those of kindred etioporphyrins compounds having a different positional isomery and central metal ions. Variations in the microscopic film morphology and crystal arrangement are poorly reflected in the absorption spectra. Archetypal thin-film photovoltaic cells with a planar donor/acceptor heterojunction where the Ni-EtioP-III donor is paired with the Cl 6 SubPc acceptor show a moderate photovoltage of 0.58 V and a short-circuit current density of 1.8 mA/cm 2 . This results in a low efficiency of no more than 1%, which is typical for planar metallo-etioporphyrins. The best photovoltaic performance with a 2.3% efficiency was measured in the cells with a non-planar vanadyl complex, VO-EtioP-III as the donor, along with a very high photosensitivity and rectification ratio of 8⋅10 5 .