Application of Supramolecular Assembly of Porphyrin Dimers for Bulk Heterojunction Solar Cells

Recently, there has been a growing interest in developing porphyrin derivatives as electron donor materials in solution-processed organic solar cells. In contrast to the traditional synthesis route, we adopt a ligand-mediated supramolecular assembly approach to produce a new soluble porphyrin derivative. The complexation of nitrogen lone pairs in the bidentate ligands to the axial orbitals of both zinc atoms in zinc-metalated porphyrin dimers (KC2s) form KC2-duplex. The UV–vis absorbance of KC2-duplex displays a red-shift of the Q-band compared with that of KC2, indicating an improvement of intermolecular interaction. By blending KC2-duplex with [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) as the photoactive material for fabricating organic bulk heterojunction solar cells, the devices demonstrate a 38.7% enhancement of short-circuit current density (<i>J</i>_sc) as compared to those made from dimers. The largely enhanced <i>J</i>_sc is attributed to the improved charge transport dynamics of KC2-duplex:PC₇₁BM blend, including the hole and effective mobilities and exciton dissociation probability. When the photoactive film is processed from solvent containing 3% v/v 1-chloronaphthalene, <i>J</i>_sc is further enhanced (∼64.5%) as well as the fill factor (16.7%) for a power conversion efficiency of 3.06% from 1.63%. Our approach shown here can be generalized to other porphyrin-related systems to advance the development of porphyrin-based optoelectronic devices