Kellen Chen

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.

Color tuning associated with heteroleptic cyclometalated Ir(III) complexes: influence of the ancillary ligand.

We report the preparation of a series of new heteroleptic Ir(III) metal complexes chelated by two cyclometalated 1-(2,4-difluorophenyl)pyrazole ligands (dfpz)H and a third ancillary bidentate ligand (L=X). Such an intricate design lies in a core concept that the cyclometalated dfpz ligands always warrant a greater pi pi* gap in these series of iridium complexes. Accordingly, the lowest one-electron excitation would accommodate the pi* orbital of the ancillary L=X ligands, the functionalization of which is then exploited to fine-tune the phosphorescent emission wavelengths. Amongst the L=X ligands designed, three classes (series 1-3) can be categorized, and remarkable bathochromic shifts of phosphorescence were observed by (i) replacing the 2-benzoxazol-2-yl substituent (1a) with the 2-benzothiazol-2-yl group (1b) in the phenolate complexes, (ii) converting the pyridyl group (2a) to the pyrazolyl group (2b) and even to the isoquinolyl group (2c) in the pyrazolate complexes and (iii) extending the pi-conjugation of the benzimidazolate ligand from 3a to 3b. Single-crystal X-ray diffraction study on complex [(dfpz)Ir(bzpz)] (2b) was conducted to confirm their general molecular architectures. Complex 2b was also used as a representative example for fabrication of multilayered, green-emitting phosphorescent OLEDs using the direct thermal evaporation technique.