A Bis(tridentate)cobalt Polypyridine Complex as Mediator in Dye‐Sensitized Solar Cells. Issue 20 (22nd June 2015)

• Record Type: Journal Article
• Authors: Mengel, Andreas K. C.; Cho, Woohyung; Breivogel, Aaron; Char, Kookheon; Soo Kang, Yong; Heinze, Katja
• Is Part Of: European journal of inorganic chemistry. Issue 20(2015)
• Page Start: 3299
• Page End: 3306
• Publication Date: 2015-06-22
• Subjects: Solar cells -- Dyes -- Sensitizers -- Electron transfer -- Redox mediators -- Cobalt -- Ruthenium; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.201500252
• Languages: English
• ISSNs: 1434-1948

Abstract

Abstract: Dye‐sensitized solar cells equipped with cationic and neutral Ru II ‐based sensitizers [Ru(ddpd){tpy(COOH)3 }] 2+ [1 2+ ; ddpd = N, N′ ‐dimethyl‐ N, N′ ‐di(pyridin‐2‐yl)pyridin‐2, 6‐diamine, tpy(COOH)3 = 2, 2″6′, 2″‐terpyridine‐4, 4′, 4″‐tricarboxylic acid] and [Ru(ddpd){tpy(COOH)(COO)2 }] (2 ) with and without the coadsorbent chenodeoxycholic acid were constructed with I3 – /I – or the Co III/II ‐based redox mediators [Co(bpy)3 ] 3+/2+ (3 3+/2+ ; bpy = 2, 2′‐bipyridine) and [Co(ddpd)2 ] 3+/2+ (4 3+/2+ ) in the presence of LiClO4 and 4‐ tert ‐butylpyridine. The best photovoltaic performance was achieved by using the4 3+/2+ shuttle and the neutral sensitizer2 without coadsorbent. The higher short‐circuit photocurrent density and higher electron recombination lifetimes obtained with this combination suggest slow electron recombination kinetics at the TiO2 surface with the Co III complex4 3+ . The slow electron transfer to4 3+ is tentatively ascribed to the high‐lying π* orbitals of the electron‐rich ddpd ligands, which result in a weak electronic coupling. This contrasts with the faster recombination with3 3+, which features the low‐energy π* orbitals of the bpy ligands. Abstract : The depicted Co 3+/2+ redox shuttle increases the short‐circuit photocurrent density I SC relative to that of the standard I3 – /I – mediator in dye‐sensitized solar cells with Ru sensitizers. The higher I SC values and electron recombination lifetimes are ascribed to the high energy of the π* orbitals of the polypyridine ligands of the mediator, which retard back electron transfer from TiO2 to the Co 3+ species.