Nanomaterials in Dye and Perovskite Sensitized Solar Cells

• Main Authors: Ying-Chiao Wang, 王映樵
• Other Authors: 陳俊維
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/8d6ktg

博士 === 國立臺灣大學 === 材料科學與工程學研究所 === 103 === First, we present the colloidal pyrite FeS2 nanocrystals (NCs), which are abundant in nature and nontoxic, have attracted attention for developing low-cost fabrications of photovoltaic (PV) devices using solution processes. This section demonstrates an important PV application using FeS2 nanocrystal pyrite ink to fabricate a cost-effective counter electrode (CE) to replace the expensive Pt counterpart in dye-sensitized solar cells (DSSCs). FeS2 NC ink has exhibited excellent electrochemical catalytic activity and remarkable stability and showed a promising power conversion efficiency (PCE) comparable to that using a Pt CE. Solution-processable and semitransparent FeS2 NC-based CEs also enable the fabrication of flexible and bifacial DSSCs. The results indicate that earth-abundant FeS2 NC ink is an extremely interesting candidate for replacing the precious metal of Pt for employing the iodide/triiodide redox couples, which can substantially lower the cost of DSSCs in future commercial applications. Next, the impedance of interception of the oxidized dye (S+) by electron donors in the electrolyte, and recombination of the electron in the dye-adsorbed mesoporous electrode with S+ or electrolyte species have been identified as the main cause of energy loss in DSSCs. Generally, an ultrathin inorganic electron blocking material surrounding working metal oxides is required to inhibit their recombination and further promoted electron-transfer reactions. However, the surface passivation interlayers would decrease adsorption of the dye resulting in reduces the interface between the dye molecules and semiconductors or decreases the quantum efficiency for electron injection, which all led to a reduced photocurrent. Here, we demonstrate an important PV application using a dual functional poly (vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer deposited onto the dye penetrant working electrode (WE) by a solution-processed method. The WE after introduced the conformal P(VDF-TrFE) interlayer have both ability of reducing carrier recombination and facilitating ionic mobility, therefore, the further enhancement of 18.7% PCE in DSSCs. These results indicate that the cost-effective P(VDF-TrFE) copolymer is an extremely interesting candidate for promoted dual functions of electron collection efficiency and S+ regeneration rate, which can substantially higher the efficiency of DSSCs in future commercial applications. In Chapter 5, organometal halide perovskite materials were identified as promising light harvesters to achieve rapidly boosted performance, providing great potential for developing low-cost next-generation photovoltaic devices. The highly crystalline perovskite is required either to absorb most of the sunlight or deliver efficient charge transport pathways for photogenerated carriers. Here, we use a sequential deposition technique for prepared perovskite crystals under various conversion ratios to demonstrate the mechanisms of an extended three-dimensional network of corner-sharing [PbI6]4- octahedral and then filled the methylammonium (MA) to 12-fold iodide coordinated interstitial sites among the octahedral by X-ray diffraction (XRD) spectrum and X-ray photoelectron spectroscopy (XPS), respectively, during crystal growth. Furthermore, the vertical distributions of morphology and crystal structure have important implication for analyzed depth profile of the perovskite structures using the XRD depth profiles and two-dimensional GIXRD spectra measurement. These results indicate that through clearly realized material engineering, and the most significant differences in efficiency are attributed to whether enhances transformation of perovskite by the orderly built the inorganic frameworks and completely inserted the organic molecules. Furthermore, to replace high-temperature sintered scaffold materials in conventional CH3NH3PbI3-based solar cells, this study demonstrates a new device structure of a bulk intermixing (BI)-typed CH3NH3PbI3/TiO2 nanorods (NRs) hybrid solar cell, where dispersed TiO2 NRs from chemical synthesis are intermixed with the perovskite absorbing layer to form a BI-typed perovskite/TiO2 NRs hybrid for device fabrication. Through interface engineering between TiO2 NR surface and the photoactive perovskite material of CH3NH3PbI3 by ligand exchange treatment, a remarkable power conversion efficiency (PCE) of over 12% was achieved based on the simple BI-typed CH3NH3PbI3/TiO2 NR hybrid device structure. The proposed hybrids not only provide great flexibility for deposition on various substrates through spin coating at low temperatures but also enable layer-by-layer deposition for future development of perovskite-based multi-junction solar cells. Finally, the utilization of iodide ligand assisted lead sulfide nanocrystal (PbS/I-) as the seeds for heterogeneous-nucleation in perovskite solar cells is demonstrated. Through interface engineering between PbS nanocrystal surface and the perovskite material of CH3NH3PbI3Cl3-x as a result of improvement crystallinity of the perovskite film and further formed large grain sized morphology by ligand exchange treatment, a remarkable power conversion efficiency of 16% was achieved. Both electron and hole diffusion length of large grain perovskite are longer than the pristine sample, indicated that the smaller trap densities in the large grain sized perovskite crystals. Therefore reduced charge transfer resistance across the perovskite material that growth from PbS/I-, so that achieved the higher fill factor and short circuit current density. Our results indicate that PbS nanocrystal could be a simple solution-processable introducing to perovskite precursor solution as the nuclei and multidentate chelation ligands in perovskite solar cells.