Electronically Tuned Asymmetric meso-Substituted Porphyrins for p-Type Solar Cells

A series of electronically tuned asymmetric porphyrins have been synthesized for use in p-type solar cells. The porphyrin derivatives were strategically designed with electron-withdrawing capability and an electronic dipole gradient to aid in electron-harvesting capacity from a nickel oxide cathode. Specifically, the porphyrins were substituted at the meso position with different arrangements of the electron-withdrawing pentafluorobenzene moiety, electron-donating/coordinating 4-pyridyl ligand, and an electron withdrawing/synthetically modifiable 4-cyanophenyl unit. Two distinct free-base porphyrins were synthesized, one of which was further metallated with nickel(II). The porphyrins were fully characterized and their electronic properties explored experimentally by electrochemistry, and both steady state and time-resolved spectroscopy. Finally, the porphyrins were incorporated into a p-type solar cell device utilizing NiO as the cathode, and demonstrating a preliminary maximum performance of η(%)=0.082 and IPCE_MAX (%)=26.0 without co-sensitization.