Metallophthalocyanines in a ternary photoactive layer (P3HT:MPc:PC70BM) for bulk heterojunction solar cells

Abstract

Novel bulk heterojunction (BHJ) organic photovoltaic (OPV) solar cells have been fabricated by introducing a series of metallophthalocyanines (MPcs) into a blend of a poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl C₇₀ butyric acid methyl ester (PC₇₀BM) photoactive layer. Sixteen MPcs have been synthesised with due consideration of the metal type and valency, functionalised ligand moieties and their respective molecular energy levels. The MPcs were expected to act as an electron cascade material that improves the photovoltaic performance in a two-fold manner: first, to provide an efficient energy level offset between the polymeric donor (P3HT) and the fullerene-based derivative acceptor (PC₇₀BM) to enhance charge transfer and reduce recombination within the OPV solar cells, and second, to harvest a greater portion of the solar spectrum as MPcs are associated with absorption near the near-infrared region. BHJ OSCs were fabricated in the following inverted configuration: ITO/TiO₂/P3HT:MPc:PC₇₀BM/WO₃/Ag and were investigated for their optimum photovoltaic performance. The BHJ OSCs comprising P3HT, PC₇₀BM and the manganese MPc (MnPc) series photoactive layer displayed the best PCEs in the range of 2.36–2.62% which were approximately 47.5–63.7% higher than those of the binary reference BHJ OSCs.