Thiocyanate-free ruthenium(ii) sensitizers with a bi-imidazole ligand in dye-sensitized solar cells (DSSCs). (14th June 2017)

• Record Type: Journal Article
• Authors: Ashraf, Saba; Akhtar, Javeed; Siddiqi, Humaira M.; El-Shafei, Ahmed
• Is Part Of: New journal of chemistry. Volume 41:Number 14(2017)
• Page Start: 6272
• Page End: 6277
• Publication Date: 2017-06-14
• Subjects: Chemistry -- Periodicals; Chimie -- Périodiques; 540
• DOI: 10.1039/c7nj01363a
• Languages: English
• ISSNs: 1144-0546

Abstract

Abstract : In this study, tris-heteroleptic Ru(ii ) sensitizers denoted asSD-15 andSD-16 with a 4, 4′, 5, 5′-tetramethyl-1 H, 1′ H -2, 2′-bis-imidazole moiety as the ancillary ligand were designed, synthesized and characterized. Abstract : In this study, tris-heteroleptic Ru(ii ) sensitizers denoted asSD-15 andSD-16 with a 4, 4′, 5, 5′-tetramethyl-1 H, 1′ H -2, 2′-bis-imidazole moiety as the ancillary ligand were designed, synthesized and characterized using FTIR-ATR, 1 H-NMR and UV-vis spectrophotometry. Structural modulations resulted in a red shift in the low-energy metal-to-ligand charge transfer (MLCT) absorption peak. The novel bis-imidazole based Ru(ii ) sensitizer was adsorbed on a TiO2 surface via –COOH anchoring groups. The band gap, and the ground and excited state oxidation potentials were measured. The photovoltaic performance of the as-fabricated solar cells was measured and showed that the presence of bis-imidazole provided more negative free energy for dye regeneration (−Δ G regeneration ) and less driving force for electron injection (−Δ G injection ) into the conduction band edge of TiO2 . Therefore, the use ofSD-15 andSD-16 resulted in lower J SC values of 10.20 and 3.52 mA cm −2, respectively, thanN719 . The open-circuit photovoltage ( V OC ) ofSD-15 andSD-16 was 0.58 and 0.52 V, respectively, less thanN719 under the same experimental conditions due to the decreased eTiO2 lifetime of 0.71 ms compared to 8.8 ms ofN719 for the injected electrons that was calculated using impedance measurements. Our efforts in this research program led to the development of more stable Ru(ii ) complexes compared toN719 NCS-based complexes; however, the conversion efficiency was lower. Hence, the fine-tuning of bi-imidazole is needed to identify more efficient NCS-free Ru(ii ) sensitizers for higher efficiency DSSCs.