Bo-So Chen

Donor–acceptor dyes with fluorine substituted phenylene spacer for dye-sensitized solar cells

A new series of organic sensitizers LJB-H, LJB-Fo and LJB-Fm with triphenylamine, 3,4-ethylenedioxythiophene plus various functionalized phenylenes, and cyanoacrylic acid as the donor, π-spacer, and anchoring group, respectively. These organic sensitizers exhibit much higher molar extinction coefficients than the parent LJ1 dye as well as reveal a remarkable fluorine substituent effect. LJB-Fm with fluoro substitution at the meta position relative to cyanoacrylic acid possesses a lower S0–S1 gap and weaker coupling with the TiO2 electrode (cf.LJB-H and LJB-Fo). Conversely, due to the resonance effect with respect to cyanoacrylic acid, the ortho-F-substituted LJB-Fo has a larger energy gap but stronger TiO2 affinity. As a result, LJB-Fo shows better DSSC performance with Jsc = 15.58 mA cm−2, Voc = 787 mV, FF = 0.67 and η = 8.22%.

Neutral, panchromatic Ru(II) terpyridine sensitizers bearing pyridine pyrazolate chelates with superior DSSC performance

A new series of neutral, panchromatic Ru(II) terpyridine sensitizers (PRT1-PRT4) exhibit much higher molar extinction coefficients at 400-550 nm and superior DSSC performance in terms of conversion efficiency (eta = 10.05 for PRT4) and stability.

Strategic design and synthesis of novel tridentate bipyridine pyrazolate coupled Ru(II) complexes to achieve superior solar conversion efficiency

A new series of tridentate bipyridine pyrazolate coupled Ru(II) complexes CK1, CK2, HY1 and HY2 were strategically designed and synthesized. In comparison to N719, CK2 and HY2 achieved the original proposal of obtaining an absorption extinction coefficient ranging from 350 to ∼550 nm, accompanied by lowering of the lowest lying energy gap. These advantages allow us to reduce the thickness of the TiO2 layer, resulting in great suppression of the dark current and hence an increase of Voc. Upon optimization, HY2 attained η = 8.07, Jsc = 15.81 mA cm−2, Voc = 753 mV and FF = 0.678, the results of which are equivalent to that of N719 (η = 8.02, Jsc = 15.70 mA cm−2, Voc = 765 mV and FF = 0.668) maximized in this study.

Self-assembly of N,N′,N″-tris(4-pyridyl)trimesic amide and N,N′,N″-tris(3-pyridyl)trimesic amide with AgI or CdII ions

We report herein an interesting family of tripyridyltriamides (L1 ≡ N,N′,N″-tris(3-pyridyl)trimesic amide, L2 ≡ N,N′,N″-tris(4-pyridyl)trimesic amide) used as tridentate bridging ligands to carry out crystal-engineering studies. The reaction of AgPF6 with L1 leads to a 2-D coordination polymer, [Ag(L1)PF6]n (1). The 48-membered macrocycles constructed from three-coordinate AgI ions as connectors and three tripyridyltriamide moieties propagate into 2-D extended structures. Indeed, the AgI⋯π interaction (the distance of the AgI⋯centroid of benzene is 3.209 A) increases the supramolecular complexity, and leads to inter-sheet dimerization. The reaction of CdCl2 with L2 forms a 3-D coordination network, [Cd(L2)2Cl2]n (2). The open channels with a diameter of ca. 7.5 A containing the tripyridyltriamide moieties propagate into 3-D extended structures. This is an interesting example of 3-D coordination networks containing tripyridyltriamides as functional moieties inside the channels. However, the channels are filled with disordered water molecules and chloride anions, where the latter are appended through hydrogen-bonding interactions with the amide moieties inside the channels. In addition, 1 displays a high-energy emission with a maximum at ca. 450 nm, whereas 2 shows a low-energy emission with a maximum at ca. 532 nm. The former with a ca. 450 nm emission is assigned to an intraligand transition, and the latter with a ca. 532 nm emission is tentatively ascribed to a metal-to-ligand charge-transfer transition.

Anion-directed assembly of supramolecular zinc(II) halides with N,N′-bis-4-methyl-pyridyl oxalamide

We report here the supramolecular structures and solid state luminescence of zinc(II) halides with N,N′-bis-4-methyl-pyridyl oxalamide (L), where the supramolecular assembly formed is dependent on the halide, and led to the formation of one-dimensional coordination polymers for Cl ([ZnCl2(L)]n) and Br ([ZnBr2(L)]n) or a discrete macrocycle for I ([ZnI2(L)]2), respectively. The rectangular structure of iodo compounds with pyridyl amide L shows an interesting nanotube framework built from π⋯π interactions in combination with hydrogen bonding. To our knowledge, these are rare examples of the anion-directed assembly of supramolecular structures. The low energy emission at ca. 500 nm for [ZnI2(L)]2 is assigned to a ligand-to-metal charge-transfer (LMCT) transition.

Design and Synthesis of Trithiophene-Bound Excited-State Intramolecular Proton Transfer Dye: Enhancement on the Performance of Bulk Heterojunction Solar Cells

In an aim to harvest UV-near-visible (360-440 nm) photons as well as to increase the morphology in the bulk heterojunction solar cells, we report herein the strategic design, synthesis, and characterization of a novel excited-state intramolecular proton-transfer dye, 3-hydroxy-2-(5-(5-(5-(3-hydroxy-4-oxo-4H-chromen-2-yl)thiophen-2-yl)thiophen-2-yl)thiophen-2-yl)-4H-chromen-4-one (FT), which bears two key functional groups, namely 3-hydroxychromone chromophore and trithiophene backbone and is then exploited into the blends of regioregular poly(3-hexylthiophene) (RR-P3HT) and phenyl-C(61)-butyric acid methyl ester (PCBM). FT acts as an excellent UV-near visible absorber, which then undergoes excited-state intramolecular proton transfer, giving rise to an orange-red proton-transfer emission that was reabsorbed by P3HT via a Forster type of energy transfer. Introduction of FT to P3HT/PCBM blend films also improves the morphology of phase separated structure, in particular, enhances the interaction of P3HT chains and the hole mobility. In this work, under the optimized condition of P3HT: PCBM:FT of 15:9:2 in weight ratio, the best performance of the device B-FT2 revealed consistent enhancements in the efficiency (eta) 4.28% and short-circuit current (J(sc)) 12.53 mAcm(-2), which are higher than that (3.68% and 10.28 mAcm(-2)) of the best performance of the control device B (P3HT:PCBM 15:9 in weight ratio) by 16 and 22%, respectively.

A new type of donor–acceptor dye bridged by the bidentate moiety; metal ion complexation enhancing DSSC performance

The bidentate 2,2′-bithiazole moiety was strategically designed as the bridging unit for the new donor–acceptor dye, Alko1. Dye sensitized solar cells (DSSCs) made by Alkol bound with various metal ions have been examined. Upon complexing with ZnI2, the Zn(II)–Alko1 complex on TiO2 achieved both higher molar absorptivity and a red-shifted absorption peak, increasing the performance of DSSCs by ∼23% (cf. metal ion free Alko1).