After over 30 years of development, surface-enhanced Raman spectroscopy (SERS) is now facing a very important stage in its history. The explosive development of nanoscience and nanotechnology has assisted the rapid development of SERS, especially during the last 5 years. Further development of surface-enhanced Raman spectroscopy is mainly limited by the reproducible preparation of clean and highly surface enhanced Raman scattering (SERS) active substrates. This review deals with some substrate-related issues. Various methods will be introduced for preparing SERS substrates of Ag and Au for analytical purposes, from SERS substrates prepared by electrochemical or vacuum methods, to well-dispersed Au or Ag nanoparticle sols, to nanoparticle thin film substrates, and finally to ordered nanostructured substrates. Emphasis is placed on the analysis of the advantages and weaknesses of different methods in preparing SERS substrates. Closely related to the application of SERS in the analysis of trace sample and unknown systems, the existing cleaning methods for SERS substrates are analyzed and a combined chemical adsorption and electrochemical oxidation method is proposed to eliminate the interference of contaminants. A defocusing method is proposed to deal with the laser-induced sample decomposition problem frequently met in SERS measurement to obtain strong signals. The existing methods to estimate the surface enhancement factor, a criterion to characterize the SERS activity of a substrate, are analyzed and some guidelines are proposed to obtain the correct enhancement factor.

Novel organic dyes (MK dyes), which have a carbazole derivative as an electron donor and a cyanoacrylic acid moiety (dC(sCtN)COOH) as an electron acceptor and an anchoring group, connected with n-hexyl-substituted oligothiophenes as a π-conjugated system, were designed and synthesized for application in dye-sensitized solar cells (DSSCs), which are one of the promising molecular photovoltaics. The photovoltaic performance of the DSSCs based on MK dyes markedly depends on the molecular structure of the dyes in terms of the number and position of n-hexyl chains and the number of thiophene moieties. Retardation of charge recombination caused by the existence of n-hexyl chains linked to the thiophene groups resulted in an increase in electron lifetime. As a consequence, an improvement of open-circuit photovoltage (V oc ) and hence the solar-to-electric power conversion efficiency (η) of DSSCs was achieved upon addition of n-hexyl chains to the thiophene groups. In addition, the adsorption condition (amount of dye molecules and/or dye aggregate thickness) on the nanoporous TiO 2 electrode, depending on the number of hexyl chains, strongly affected the performance of DSSCs. A larger amount and/or thicker aggregate of dye molecules brought about longer electron lifetime, which resulted in higher V oc , and slower diffusion of I 3 ions in the nanoporous TiO 2 electrode, which led to lower short-circuit photocurrent (J sc ) and fill factor (FF). In the result of thorough investigation on the series of MK dyes, a DSSC based on MK-2 consisting of n-hexyl-substituted quarter-thiophene produced 8.3% of η (J sc ) 15.22 mA cm -2 , V oc ) 0.73 V, and FF ) 0.75) under 100 mW cm -2 simulated AM1.5G solar irradiation.

1H,4H,10H-11-oxa-3a-aza-benzo[de]anthracen -9-yl)-thiophen-2-yl]-vinyl}-thiophen-2-yl)-acrylic acid (NKX-2700), and its application in dye-sensitized solar cells (DSSCs). Under illumination of simulated AM1.5G solar light (100 mW cm -2 ) with an aperture black mask, 5.0% of power conversion efficiency [short-circuit photocurrent density (J sc ) ) 12.0 mA cm -2 , open-circuit photovoltage (V oc ) ) 0.59 V, and fill factor (FF) ) 0.71] was obtained for NKX-2700 based DSSC, which was significantly improved to 8.2% (J sc ) 15.9 mA cm -2 , V oc ) 0.69 V, FF ) 0.75) upon addition of 120 mM deoxycholic acid (DCA) to the dye solution for TiO 2 sensitization. Coadsorption of DCA decreased dye coverage by ∼50% but significantly improved the J sc by 33%. The breakup of π-stacked aggregates might improve electron injection yield and thus J sc . Electrochemical impedance data indicate that the electron lifetime was improved by coadsorption of DCA, accounting for the significant improvement of V oc . These results suggest that interfacial engineering of the organic dye-sensitized TiO 2 electrodes is important for highly efficient photovoltaic performance of the solar cell.