Palladium(II) and Platinum(II) Porphyrin Donors for Organic Photovoltaics

Three new A-pi-D-pi-A structural porphyrin-based donors, C19-H2P, C19-PdP, and C19-PtP, are designed and synthesized, with porphyrin (D) moieties equipped with no metal, palladium (Pd), and platinum (Pt) as the core, respectively, and end-capped with electron-deficient 3-ethylrhodanine (A) via a pi-bridge of phenylene ethynylene linker. C19-PdP and C19-PtP exhibit low-lying highest occupied molecular orbital levels than C19-H2P. The three porphyrin donors show highly intensified and broad absorptions at ca. 400-530 nm (Soret bands) and at ca. 550-800 nm (Q-bands) with an absorption valley at ca. 540 nm. Using PC71BM as an electron acceptor, the devices based on C19-PdP and C19-PtP donors achieve power conversion efficiencies (PCEs) of 8.09 and 7.31% under 1 Sun, respectively, whereas the C19-H2P device, that has no metal, has a very low PCE of 2.51%. Furthermore, at 300 lux LED source, the C19-PdP and C19-PtP devices deliver promising PCEs of 16.54 and 16.74%, respectively. The improved performance of C19-PdP- and C19-PtP-based devices is mainly due to more efficient charge collection, faster charge transport, more suppressed recombination behavior, and smoother surface morphology. These findings pave the way for the development of new metalloporphyrin-based donors for organic solar cells using simple structural engineering.