Cyclometalated Platinum-Containing Diketopyrrolopyrrole Complexes and Polymers: Photophysics and Photovoltaic Applications

A series of organometallic complexes and polymers has been synthesized with an objective of studying their fundamental photophysical properties together with their organic photovoltaic and organic field-effect transistor properties. The metal chromophores consist of a diketopyrrolopyrrole (DPP) core, end functionalized with cyclometalated platinum “auxochrome”. The photophysical properties of the metal complex and polymers are compared with the unmetalated chromophore DPP-C8-Th-Py. The polymers Poly-DPP-Th-Pt and Poly-DPP-Ph-Pt differ structurally in their cyclometallating ligands, where they consist of 2-thienylpyridine and 2-phenylpyridine, respectively. Efficient solar spectrum coverage was observed for all chromophores; specifically, the polymer Poly-DPP-Th-Pt has an onset of absorption at ∼900 nm with an optical band gap of 1.4 eV. The triplet excited state was detected for all chromophores and probed by both nanosecond and picosecond transient absorption spectroscopy. Both polymers were employed as donors in bulk-heterojunction solar cells with a polymer:PC71BM ratio of 1:7. The thiophene-containing polymer Poly-DPP-Th-Pt shows a respectable power conversion efficiency (PCE) of 1.66% with a high fill factor (FF) of ∼66%. Higher charge carrier mobility was observed for Poly-DPP-Th-Pt when used in field-effect transistors compared to Poly-DPP-Ph-Pt.