Nanocrystalline TiO2-based Solar Cells Research Articles

Synthesis and characterization of novel cyclometalated iridium(III) complexes for nanocrystalline TiO 2-based dye-sensitized solar cells

Four novel cyclometalated iridium(III) complexes with the following general formulas were synthesized and characterized using 1H NMR, { 1H– 1H} COSY, ESI-MS spectral and elemental analysis data: [Ir(C ∧N ∧C)(ptpy-COOH)] + (C ∧N ∧C = 2,6-diphenylpyridinato ( 1); 2,4,6-triphenylpyridinato ( 2), ptpy-COOH = 4′-(4-carboxyphenyl)-2,2′:6′,2“-terpyridine) and [Ir(C ∧N ∧C)(tpy-COOH)] + (C ∧N ∧C = 2,6-diphenylpyridinato ( 3); 2,6-ditolylpyridinato ( 4), tpy-COOH = 4′-carboxy-2,2′:6′,2″-terpyridine). The photophysical and redox properties and photovoltaic performance of the Ir(III) complexes as photosensitizers in nanocrystalline TiO 2-based solar cells were studied and compared to those of cis-diisothiocyanatobis(4,4′-dicarboxy-2,2′-bipyridine)ruthenium(II) ( N3). Dye 4 exhibits the highest photovoltaic performance with an overall solar energy conversion efficiency of 2.16%.

Efficient Panchromatic Sensitization of Nanocrystalline TiO2-based Solar Cells Using 2-Pyridinecarboxylate-substituted Ruthenium(II) Complexes

Abstract Ruthenium(II) complexes containing a 2-pyridinecarboxylate ligand (1 and 2) were synthesized as sensitizers for dye-sensitized solar cells (DSCs). The solar cells containing 2 exhibited efficient panchromatic sensitization over the entire visible wavelength range, extending into the near-IR region. An overall solar light-to-electrical conversion efficiency of 9.66% was achieved under standard air mass (AM) 1.5 irradiation (100 mW cm−2). This efficiency was superior to that of black dye (9.58%) under the same cell fabrication and measuring procedure.

A novel ruthenium sensitizer with a hydrophobic 2-thiophen-2-yl-vinyl-conjugated bipyridyl ligand for effective dye sensitized TiO2 solar cells

A hydrophobic and 2-thiophen-2-yl-vinyl-conjugated ruthenium complex, cis-Ru(dhtbpy)(dcbpy)(NCS)2 [dhtbpy = 4,4'-di(hexylthienylvinyl)-2,2'-bipyridyl; dcbpy = 4,4'-dicarboxy-2,2'-bipyridyl], was newly designed, synthesized and applied successfully to sensitization of nanocrystalline TiO2-based solar cells, giving a conversion efficiency of 9.5% under irradiation with AM 1.5 solar light.

Molecular design of ruthenium(II) polypyridyl photosensitizers for efficient nanocrystalline TiO 2 solar cells

Transition metal complexes using polypyridine ligands are finding increasing use in the dye sensitized solar cells. To improve further the efficiency of this cell, an enhanced spectral response of the sensitizer in the lower energies is required. In this paper we review our effort in the molecular design of the ruthenium polypyridyl complexes for nanocrystalline TiO 2-based solar cells. The poor cell efficiency in Ru(4,4′-dicarboxy-2,2′-biquinoline) 2(NCS) 2/TiO 2 system may be ascribed to the low excited-state oxidation potential, which plays a crucial role in the electron-transfer process. Ru(2-(2-(4-carboxypyridyl))-4-carboxyquinoline) 2(NCS) 2, when anchored to nanocrystalline TiO 2 films, achieves efficient sensitization over the whole visible range extending up to 900 nm, yielding incident photon-to-current conversion efficiency (IPCE) of 55%. The low cell efficiency of Ru(4-4′-dicarboxy-2,2′-bypyridine) 2(ethyl-2-cyano-3,3-dimercaptoacrylate) may be due to slow regeneration of the dye by electron donation from iodide following charge injection into the TiO 2. Tuning of HOMO and LUMO energy level show that an efficient sensitizer should possess ground-state and excited-state redox potentials of 0.5 and −0.8 V vs. SCE, respectively. Transient absorption studies of Ru phenanthroline complexes show that the efficiency of electron injection is strongly affected by the number of carboxyl groups of the sensitizing dye. The β-diketonate complex [Ru(4-4′-dicarboxy-2,2′-bypyridine) 2(acetylacetonato)]Cl, when anchored to nanocrystalline TiO 2 films, achieves very efficient sensitization across the entire visible region, yielding 60% IPCE. A new series of panchromatic sensitizers of Ru(tricarboxyterpyridine)(β-diketonato)(NCS) type have been developed. Ru(4,4′,4″-tricarboxy-2,2′:6′,2″-terpyridine)(1,1,1-trifluoropentane-2,4-dionato)(NCS) achieved an efficient sensitization of nanocrystalline TiO 2 solar cells over the whole visible range extending into near IR region and displaying a maximum around 600 nm, where IPCE approaches a high value of 70%.

Separation of linkage isomers of trithiocyanato (4,4′,4″-tricarboxy-2,2′,6,2″-terpyridine)ruthenium(II) by pH-titration method and their application in nanocrystalline TiO2-based solar cells

A new series of panchromatic ruthenium(II) sensitizers derived from carboxylated terpyridyl complexes of tris-thiocyanato Ru(II) have been developed. The linkage isomers {(C4H9)4N}3[Ru(Htcterpy)(–NCS)3] 1, {(C4H9)4N}3[Ru(Htcterpy)(–NCS)2(–SCN)] 2 and {(C4H9)4N}3[[Ru(Htcterpy)(–SCN)3] 3 have been separated by pH titration method and fully characterized by UV–Vis, emission, IR and NMR studies. The absorption and emission maxima of the isomer 1 show a bathochromic shift with decreasing pH, and exhibit pH-dependent excited state lifetimes. The red-shift of the emission maxima is due to better π-acceptor properties of the acid form that lowers the energy of the CT excited state. The isomer 1, when anchored to nanocrystalline TiO2 films achieves very efficient sensitization over the whole visible range extending into the near IR region up to 920 nm, yielding over 80% incident photon-to-current conversion efficiencies (IPCEs). Solar cells containing the isomer 1 were subjected to analysis by a photovoltaic calibration laboratory (NREL, USA) to determine their solar to electric conversion efficiency under standard AM 1.5 sunlight. A short circuit photocurrent density obtained was 20.5 mA/cm2 and the open circuit voltage was 0.72 V corresponding to an overall conversion efficiency of 10.4%.