No abstract

We present herein a facile one-step low-temperature hydrothermal approach for in situ growth of metal selenides (Co(0.85)Se and Ni(0.85)Se) on conductive glass substrates. The as-prepared metal selenides on conductive substrates can be used directly as transparent counter electrodes for dye-sensitized solar cells (DSSCs) without any post-treatments. It is found that graphene-like Co(0.85)Se exhibits higher electrocatalytic activity than Pt for the reduction of triiodide. As a consequence, the DSSC with Co(0.85)Se generates higher short-circuit photocurrent and power conversion efficiency (9.40%) than that with Pt.

We designed and synthesized new alkyl-functionalized organic dyes, MK-1 and MK-2, for dye-sensitized solar cells (DSSCs). Based on the MK-2 dye, a high performance of efficiency (eta, 7.7%; short-circuit current density Jsc = 14.0 mA cm-2, open-circuit voltage Voc = 0.74 V, and fill factor FF = 0.74) was achieved under AM 1.5 G irradiation (100 mW cm-2). Remarkably, the relatively higher Voc for DSSCs based on MK-1 and MK-2 dyes, which have long alkyl chains, were observed among the organic dyes caused by the increasing of the electron lifetime in the conduction band of TiO2. Our molecular design of alkyl-functionalized dyes strongly suggests the promising performance of molecular photovoltaics based on organic dyes.

A novel concept "D-A-π -A" organic sensitizer instead of traditional D-π -A ones is proposed. Remarkably, the incorporated low bandgap, strong electronwithdrawing unit of benzothiadiazole shows several favorable characteristics in the areas of light-harvesting and effi ciency: i) optimized energy levels, resulting in a large responsive range of wavelengths into NIR region; ii) a very small blue-shift in the absorption peak on thin TiO 2 fi lms with respect to that in solution; iii) an improvement in the electron distribution of the donor unit to distinctly increase the photo-stability of synthetic intermediates and fi nal sensitizers. The stability and spectral response of indoline dye-based DSSCs are improved by the strong electron-withdrawing benzothiadizole unit in the conjugation bridge. The incident-photon-conversion effi ciency of WS-2 reaches nearly 850 nm with a power conversion effi ciency as high as 8.7% in liquid electrolyte and 6.6% in ionic-liquid electrolyte.

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.

Dye-sensitized solar cells [1] (DSSCs) have been studied extensively as potential alternatives to conventional inorganic solid solar cells, by using wide-bandgap nanocrystalline TiO 2 sensitized with ruthenium polypyridine complexes [2][3][4][5][6] or metal-free organic dyes [7][8][9][10][11][12] as photoelectrodes. Through molecular design, ruthenium complexes have achieved power-conversion efficiencies of over 11 %, [2,3,13] while metal-free organic dyes have reached ca. 9 % power-conversion efficiency under AM 1.5 (AM: air mass) simulated solar light of 100 mW cm -2(1 sun). [14,15] Several ruthenium polypyridyl complexes haveshown their ability to withstand thermal or light-soaking stress tests for at least 1000 h while retaining an efficiency above 7 %, [16][17][18] whereas for organic-dye-based DSSCs the longterm stability, which is the critical requirement for practical applications, so far remains a serious problem. Organic dyes are also promising for applications in DSSCs in that they have much higher molar extinction coefficients [19][20][21] than those for ruthenium polypyridine complexes, which are favorable for light-harvesting efficiency (LHE) and hence photocurrent generation. Among the organic dye sensitizers tested in DSSCs, coumarin dyes are strong candidates because of their good photoelectric conversion properties. [8,22] However, one of their drawbacks is that a high concentration of 4-tert-butylpyridine (TBP) is usually required for a high power-conversion efficiency. [22] Under continuous light soaking of 1 sun for a short period of one day, the photovoltaic performance was observed to drop dramatically because of the dissolution of the dye into electrolyte containing 0.5 M or more TBP. Therefore, it still remains a great challenge to acquire a DSSC based on a metal-free organic dye with high efficiency that is stable in the long term. In this paper, we report a new coumarin dye, 2-cyano-3-{5′-[1-cyano-2-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6-tetrahydro-1H,4H,10H-11-oxa-3a-aza-benzo These DSSCs exhibited LHE values of near unity, incident photon-to-electron conversion efficiency (IPCE) over a wide spectral region on transparent TiO 2 films of only 6 lm thickness, and maintained ca. 6 % power-conversion efficiency under continuous light soaking of 1 sun at 50-55°C for 1000 h. Figure 2a shows the UV-vis absorption spectrum for NKX-2883 in an ethanol solution. NKX-2883 exhibited two p-p* electron-transition peaks (426 and 552 nm) in the visible region. Compared to NKX-2677 (2-cyano-3-[5'-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6-tetrahydro-1H,4H,10H-11-oxa-3a-azabenzo [de]anthracen-9-yl)-[2,2']bithiophenyl-5-yl]acrylic acid), one of the best organic dyes for DSSCs reported previously, [22] the introduction of one more CN group into the molecular frame decreases the gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), thus extending the maximum absorption from 511 to 552 nm. This red-shift may favor light harvesting and hence photocurrent generatio...

This paper describes the influence of acid pretreatment ofTiO2 mesoporous films prior to dye sensitization on the performance of dye-sensitized solar cells based on [(C4H9)4N]3[Ru(Htcterpy)(NCS)3] (tcterpy = 4,4',4"-tricarboxy- 2,2',2"-terpyridine), the so-called black dye. The HCl pretreatment caused an increase in overall efficiency by 8%, with a major contribution from photocurrent improvement. It is speculated, from the analysis of incident photon-to-electron conversion efficiency, UV-vis absorption spectra, redox properties of the dye and TiO2, and the impedance spectra of the dye-sensitized solar cells, that photocurrent enhancement is attributed to the increases in electron injection and/or charge collection efficiency besides the improvement of light harvesting efficiency upon HCl pretreatment. Open-circuit photovoltage (V(oc)) remained almost unchanged in the case of significant positive shift of flat band potential for TiO2 upon HCl pretreatment. The suppression of electron transfer from conduction band electrons to the I3- ions in the electrolyte upon HCl pretreatment, reflected by the increased resistance at the TiO2/dye/electrolyte interface and reduced dark current, resulted in a V(oc) gain, which compensated the V(oc) loss due to the positive shift of the flat band. Using the HCl pretreatment approach, 10.5% of overall efficiency with the black dye was obtained under illumination of simulated AM 1.5 solar light (100 mW cm(-2)) using an antireflection film on the cell surface.

A new coumarin dye, cyano-{5,5-dimethyl-3-[2-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6-tetrahydro-1H,4H,10H-11-oxa-3a-aza-benzo[de]anthracen-9-yl)vinyl]cyclohex-2-enylidene}-acetic acid (NKX-2753), was prepared and characterized with respect to photophysical and electrochemical properties. It was employed as a dye sensitizer in dye-sensitized solar cells and showed efficient photon-to-electron conversion properties. The photocurrent action spectrum exhibited a broad feature with a maximum incident photon-to-electron conversion efficiency (IPCE) of 84% at 540 nm, which is comparable to that for the famous red dye RuL2(NCS)2 (known as N3), where L stands for 2,2'-bipyridyl-4,4'-dicarboxylic acid. The sandwich-type solar cell with NKX-2753, under illumination of full sun (AM1.5, 100 mW cm(-2)), produced 16.1 mA cm(-2) of short-circuit photocurrent, 0.60 V of open-circuit photovoltage, and 0.69 of fill factor, corresponding to 6.7% of overall energy conversion efficiency using 0.1 M LiI, 0.05 M I2, 0.1 M guanidinium thiocyanate, and 0.6 M 1,2-dimethyl-3-n-propyl-imidazolium iodide in dry acetonitrile as redox electrolyte. In comparison with its analogue NKX-2586 (Langmuir 2004, 20, 4205), NKX-2753 with an extra side ring on the alkene chain produced much higher IPCE values at the same conditions. The side ring acted as a spacer to efficiently prevent dye aggregation when adsorbed on the TiO2 surface, resulting in significant improvements of short-circuit photocurrent, open-circuit photovoltage, and fill factor compared with NKX-2586 that aggregated on the TiO2 surface.