Title

Heteroleptic osmium(II) polypyridine complexes and carbazole-based chromophores as sensitizers in dye-sensitized solar cells

Date of Award

2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Photochemical Sciences

First Advisor

Felix N. Castellano, Ph.D

Second Advisor

Margaret M. Yacobucci, PhD (Committee Member)

Third Advisor

John R. Cable, PhD (Committee Member)

Fourth Advisor

Thomas H. Kinstle, PhD (Committee Member)

Abstract

Several osmium(II) polypyridine complexes bearing modified terpyridine and bipyridine ligands were designed, synthesized and characterized in this work. The photophysical and electrochemical properties of the complexes were studied and the results confirm the suitability of these complexes to serve as sensitizers in dye-sensitized solar cells (DSSCs). Operational DSSCs incorporating these complexes as sensitizers were fabricated and the photovoltaic properties of these sensitizers were evaluated. Device photovoltaic properties were acquired by measuring the external quantum efficiency (EQE) as a function of wavelength and the current-voltage (I-V) curves, the latter under simulated AM1.5G one sun illumination. Initial photovoltaic evaluation of their associated solar cells indicated that TD-1 has the best photovoltaic properties. Further device optimization was carried out using this sensitizer. It was demonstrated that the photovoltaic properties of the Os(II)-based sensitizers can be improved by making variations in the composition of the redox electrolyte used in the operational DSSCs. The results indicate that an abundance of I- appears to be crucial for the effective regeneration of surface-bound osmium sensitizers and hence the production of higher photocurrents in these devices. Most importantly, an unprecedented power conversion efficiency for an Os(II)-based DSSC of 5.03% was achieved with the TD-1 sensitizer. Electrochemical and photovoltaic studies were also carried out on sensitizers based on metal-free carbazole-based chromophores. Two of the sensitizers incorporate a carbazole linker and displayed impressive photovoltaic properties with EQE's of about 75%, fill factors above 70% and power conversion efficiency of 2.70%. Short-term light-soaking indicated the potential stability of these sensitizers towards prolonged exposure to solar irradiation.