| This dissertation systemically investigates the synthesis and characterization of the urchin-like Zn/ZnO micro-nano structure as well as the fabrication and analysis of related dye-sensitized solar cells (DSSCs) devices. The influence of annealing time in the sintering process on the micro morphology and micro structure of the urchin-like Zn/ZnO photoanodes were explored. Based on the continuity equation, a dynamic IMVS model correlating to the unique urchin-like configuration is developed for the first time. Intriguingly, the photoanodes with different micro morphology and micro structure generated by tuning the annealing time, show significant discrepancies in electron transport time, recombination lifetime, charge collection efficiency and subsequently photovoltaic performance of the solar cells. Besides, this dissertation systemically investigates the synthesis and characterization of the planar heterojunction perovskite solar cells (PSCs) as well as the fabrication and analysis of related devices prepared under open air conditions. Based on the continuity equation, a dynamic IMVS model correlating to the unique planar configuration is developed for the first time.Air-annealing on the perovskite absorber layer (CH3NH3PbI3),resulting in crystallographic changes, variation in grain domain size and crystallinity, could suppress carrier recombination and prolong charge lifetime, which can yield more photo-generated electrons to be collected by anode, subsequently resulting in strikingly improving photovoltaic performance of the devices. The study could provide new insights into the performance-improving steps for the PSCs prepared under fully open air conditions, which is of great importance for their future commercialization. The following is the main contents of this dissertation.(1) The urchin-like Zn/ZnO micro-nano structure have been synthesized via the sintering process for DSSCs applications. Compared to traditional ZnO nanowire arrays,the urchin-like Zn/ZnO nanostructuresshowed preferable photoelectric properties as the anode of dye-sensitized solar cells, which can beattributed to its special geometric morphologies :i) The photoanode with a highly branched network possesses higher higher specific surface when compared with the 1D nanostructures, leading to the enrichment of dye loading and subsequently increase of light absorption. Moreover, the geometry of ordered sea urchin-like nanostructures possesses larger pores, which can provide an effective path for electrolyte diffusion without sacrificing electron-transport properties; ii) The 1-D ZnO nanowires in the urchin can act as high-speed channels for electron because of less defect, resulting in supession of electron recombination; iii)Due to the Schottky barrier formed at the Zn/ZnO interface, electron would be apt to flow into the Zn core from ZnO nanowires continuously, attributed to the lower Fermi energy in Zn and the metal core acting as an electron sink. The improvement in short-circuit current (Jsc), fill factor (FF) and the conversion efficiency (η) of the solar cells can be attributed to the reasons mentioned before.(2) Based on the urchin-like Zn/ZnO photoanode and the continuity equation, a dynamic IMVS model correlating to the unique urchin-like configuration is developed for the first time in order to explore the electron transport/recombination process. The satisfactory fits between the theoretical model and the experimental IMVS response bear out that the correctness of our IMVS dynamic model. Intriguingly, the photoanodes with different micro morphology, structure and crystallinity generated by tuning the annealing time, show significant discrepancies in electron transport time, recombination lifetime, charge collection efficiency and subsequently photovoltaic performance of the solar cells ascribed to the difference in defect states and surface states at the interface.(3) A facile low-pressure in situ vapor-assisted solution process is to fabricate the planar perovskite solar cell (PSCs) under fully open-air conditions. Compared to solution-based spin-coating route including a one-step and two-step process,CH3NH3PbI3 film synthesized using vapor-assisted solution process were flatly laminated and extremely dense with a high degree of uniformity. Moreover, in order to explore the influence of air-annealing on CH3NH3PbI3 layer, we compared the Ⅰ-Ⅴcharacteristic of the two samples with and without air-annealing, due to the fact that annealing can promote the growth of CH3NH3PbI3 crystal,resulting in decrease of grain boundary and improvement in crystallinity.(4) We construct a dynamic intensity modulated photovoltage spectroscopy (IMVS)model correlating to the unique planar PSC configuration using a continuity equation.Compared to the typical IMVS model based on dye-sensitized solar cells (DSSCs), the better IMVS fitting results presented in this study indicated that there was a discrepancy between the planar perovskite devices and those of DSSCs in electron transport/recombination properties, because carrier transfer across the TiO2/liquid electrolyte interface in DSSCs has been modified. Besides, the interface exhibits a more significant role in determining the carrier transport/recombination process by influencing the boundary conditions in a continuity equation. Furthermore, the intensity modulated photocurrent/photovoltage spectroscopy responses demonstrated that the carrier recombination characteristic is ultimately related with the surface and defect density in the interface. Air-annealing on CH3NH3PbI3 film,resulting in variation in micro morphology, crystallinity and grain domain size, could suppress carrier recombination and prolong charge lifetime, which can yield more photo-generated electrons to be collected by anode, subsequently resulting in strikingly improving photovoltaic performance of the devices. Since charge recombination mainly occurs at the interfaces via surface/defect states, interfacial modification and even careful interface design could be the key approaches to obtain highly efficient PSCs. |
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