Designing Push-Pull Porphyrins for Efficient Dye-Sensitized Solar Cells

Over the past decade, tremendous effort has been made to improve the light-harvesting ability of push-pull porphyrin dyes. Despite notable success achieved in this direction, push-pull porphyrin dyes still suffer from a poor light-harvesting efficiency owing to the lack of absorption between the Soret and Q-bands. To tackle this issue, here we design a series of push-pull porphyrin dyes with anchoring groups either at meso- or beta-position using calculations based on first-principles time-dependent density functional theory. In contrast to the common perception, we find that porphyrin dyes bearing an electron-donor at the meso-position and an electron-acceptor at the beta-position produce an additional extended band between the Soret and Q-bands appearing at around 500 nm due to S-0 -> S-3 excitation, leading to a much higher light-harvesting performances compared to meso- and beta-disubstituted ones. In addition, changing the pi-conjugated linker at the acceptor site from ethylene linker (C=C) to acetylene linker (C C) further improves the light-harvesting ability of meso-beta-porphyrin dyes, making them promising candidates for dye-sensitized solar cell application.