| After TiO2 nanocrystals were put to use in dye sensitized solar cell, the power conversion efficiency (PCE) has been delivered to above 10% at the current stage after persistent optimization. Nanomaterial synthesis, nanostructure assembly and interfacial engineering have played and will continue to play an imperative role in improving the performance of sensitized solar cell. For a significant improvement of PCE, the materials and nanostructure should be multifunctional and highly compatible in the device. In my thesis project, I focused on the understanding and the building up of photoanode materials to improve light harvesting and charge collection, and ultimately improve the overall solar cell performance.;In chapter 3, I report the development of a novel double layered photoanode for dye sensitized solar cell made of highly crystalline TiO2 octahedral nanocrystals and agglutinate mesoporous TiO2 microspheres. This double layered photoanode has taken into consideration a number of disparate factors aiming at enhancing the overall DSSC performance. Drawing on the judicious combination of materials synthesis and engineering of nano-architectures and interfaces, solar cells based on this double layered structure have achieved 8.72% power conversion efficiency even with simple device fabrication procedures, showing promise as a new photoanode design for high efficiency dye sensitized solar cells.;In chapter 4, I have significantly improved open circuit voltage and fill factor with Pt counter electrode of quasi-solid state quantum dot sensitized solar cells (QDSSCs) by achieving compact coverage of QDs on TiO2 matrix through a linker seeding chemical bath deposition process, leading to 4.23% power conversion efficiency, nearly two times that with conventionally deposited control photoanode.;Chapter 5 demonstrates the first use of a quasi-quantum well (QW) structure (ZnSe/CdSe/ZnSe) as the sensitizer, which is quasi-epitaxially deposited on ZnO tetrapods. Such a novel photoanode architecture has attained 6.20% PCE, among the highest reported to date for this type of SSSCs. This study together with the impedance spectra and intensity modulated photocurrent spectroscopies supports a core-shell two-channel transport mechanism in this type of solar cells and further suggests that the electron transport along sensitizer can be considerably accelerated by the QW structure employed.;The research in chapter 6 builds on the work of the QW structure in Chapter 5. Because the previous aqueous synthesis of the QW structure failed to generate photoluminescence (PL) from CdSe, presumably stemming from the low crystallinity and numerous defects, I opted to develop an organic solution process coupled with a layer-by-layer approach at much higher temperature to synthesize the QW structure. Well to my expectation, strong PL was observed even with the naked eye. Through optimization of the QW structure, the ZnSe/CdSe/ZnSe sandwiched QW supported on the ZnO tetrapod (ZnO/QW) showed 17 times stronger PL than the ZnSe/CdSe heterojunction (HJ) supported on the ZnO tetrapod (ZnO/HJ) at single particle level. Ensemble measurements also showed 10 times stronger PL of the former than the latter. (Abstract shortened by UMI.). |
