Photosensitizing porphyrin–triazine compound for bulk heterojunction solar cells

Abstract

This report describes the synthesis of a novel porphyrin–triazine compound bearing three porphyrin macrocycles connected to each other via a triazine central unit, and investigation of its properties for possible use in bulk heterojunction solar cells (BHJ-SCs). The porphyrin macrocycles serve as light harvesting antennae, while the triazines have been widely known to be charge extracting promoters. According to cyclic voltammetric studies, the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) energy levels of the target compound were estimated to be at −5.4 and −3.5 eV versus vacuum, respectively. Photoluminescence measurements of the blended films of the porphyrin–triazine compound and phenyl-C₆₁-butyric acid methyl ester (PCBM) or poly(3-hexylthiophene) (P3HT) indicated that the charge transfer was possible when the target porphyrin was used as an electron donor together with PCBM as an acceptor. Additionally, the surface morphology of the films with different donor : acceptor ratios was investigated by atomic force microscopy (AFM). Upon variation of the donor : acceptor weight ratio and thickness of the organic layer, the short circuit current density (J_SC) of the BHJ-SCs fabricated herein improved up to approximately 2.25 mA cm⁻².