title: Natural chlorophyll-related porphyrins and chlorins for dye-sensitized solar cells.
abstract: Natural-chlorophyll-related porphyrins, including (2H, Zn, Cu)-protoporphyrin IX (Por-1) and Zn-mesoporphyrin IX (Por-2), and chlorins, including chlorin e₆ (Chl-1), chlorin e₄ (Chl-2), and rhodin G₇ (Chl-3), have been used in dye-sensitized solar cells (DSSCs). For porphyrin sensitizers that have vinyl groups at the β-positions, zinc coordinated Por-1 gives the highest solar-energy-to-electricity conversion efficiency (h) of up to 2.9%. Replacing the vinyl groups of ZnPor-1 with ethyl groups increases the open-circuit voltage (V(oc)) from 0.61 V to 0.66 V, but decreases the short-circuit current (J(sc)) from 7.0 mA·cm⁻² to 6.1 mA·cm⁻² and the value of h to 2.8%. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations suggest that the higher J(sc) values of Zn-based porphyrin sensitizers result from the favorable electron injection from the LUMO at higher energy levels. In the case of the chlorin sensitizers, the number of carboxyl protons has a large effect on the photovoltaic performance. Chl-2 with two carboxyl protons gives much higher values of J(sc), V(oc), and h than does Chl-1 with three carboxyl protons. Replacing the protons of Chl-1 with sodium ions can substantially improve the photovoltaic performance of Chl-1-based solar cells. Furthermore, the sodium salt of Chl-3 with an aldehyde group at the C7 position shows poorer photovoltaic performance than does the sodium salt of Chl-1 with methyl groups at the C7 position. This is due to the low light-harvesting capability of Chl-3.
authors.affiliation: Research Center for Organic Electronics, Graduate School of Engineering, Yamagata University, 4-3-16 Jonan, Yonezawa, Yamagata 992-8510, Japan. xf-wang@yz.yamagata-u.ac.jp
authors.forename: Xiao-Feng
authors.initials: XF
authors.lastname: Wang
authors.forename: Osamu
authors.initials: O
authors.lastname: Kitao
mesh_terms: D002734:Chlorophyll / Q000737:chemistry*; D004563:Electrochemistry; D055668:Photochemical Processes; D011166:Porphyrins / Q000737:chemistry*; D012993:Solar Energy
chemical_list: D011166:Porphyrins; D002734:Chlorophyll; C006969:chlorin