| Dye-sensitized solar cells (DSSCs) have garnered considerable attention within the solar cell community. With comparatively low manufacturing cost, ease of fabrication, and fair solar-to-electrical efficiency, these cells are potential candidates to replace conventional Si-based solar cells in specialized applications However, since the pioneering work in 1991, the efficiencies of these cells, featuring I-/I3- as the redox shuttle, have evidently platued at around 11%, due partially to the overpotential needed for this shuttle to regenerate electrons to the ground state of dyes.;Kinetically fast redox shuttles are typically employed to reduce this energy loss but they also suffer from increasing dark current. Inorganic blocking layers were gernerally used to slow this electron transfer process. The work in the first part of my thesis will explain my attempts to understand the role of inorganic blocking layers in DSSCs. Atomic layer deposition (ALD) was utilized to deposit inorganic blocking layers on SnO2 photoanodes. It was found that only one cycle of Al2O3 deposited by ALD is sufficient to passivate catalytic surface states on SnO2 electrodes and dramatically improves the overall performance by nearly five-fold. Subsequent layer mainly acts as electron tunneling barrier. Other types of inorganic blocking layer were deposited via ALD. A linear relationship between the tunneling parameter, beta, and the square root of the band-edge difference of electrode and blocking layer was found, suggesting conformal coating of the blocking layer on the electrode.;The second part of my thesis describes works on quantifying charge collection lengths of the devices, featuring several types of porphyrin dyes in standard iodide electrolyte, through an optical measurement method. It was found that charge collection length depends on the identity of the dye and that most porphyrin dyes engender charge collection length shorter than actual thickness of the cells, suggesting exceptionally fast electron recombination. This rapid electron recombination was proposed to occur from a pseudo-complex between porphyrin and tri-iodide. Finally, a series of conjugated porphyrin dyes were explored with a p-Type DSSC configuration. The photocatalytic activity of tri-iodide was observed instead of an expected cathodic current. Possible explanations are explained herein. |
