On the potential of porphyrin-spiked triarylamine stars for bulk heterojunction solar cells

Abstract

A novel porphyrin–triarylamine compound was synthesized to serve as a photosensitizer in bulk heterojunction solar cells (BHJ-OSCs). Based on cyclic voltammetric analysis, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the target porphyrin trimer were determined to be at −5.4 and −3.5 eV versus vacuum, respectively, and compared with those of other materials used for the construction of the BHJ-OSCs. Absorption and emission spectra of the film of the target porphyrin trimer were in good agreement with those of its solution. The charge transfer in a blended film of the porphyrin–triarylamine compound with phenyl-C₆₁-butyric acid methyl ester (PCBM) was proven possible by photoluminescence measurements. The energy conversion efficiency of the BHJ-OSCs based on the target compound depended strongly on the donor : acceptor weight ratio and the thickness of the organic layer. Surface nanomorphologies of the films with different donor : acceptor ratios and thickness were investigated by atomic force microscopy (AFM). The short circuit current density (J_SC) up to 2.06 mA cm⁻² was obtained from the BHJ-OSC fabricated herein.