Preparation And Photovoltaic Performance Of The Compact TiO₂ Layer And Perovskite Absorber Layer

In this thesis,2 mol·L-1 TiCl4 aqueous stock solution was diluted with the isopropanol by different volume to obtain the metastable TiCl4 isopropanol/water solution. The solution was spin-coated and subsequently hydrolyzed at 130℃ to prepare the compact TiO2 layers, and the perovskite solar cells with the architecture of FTO/c-TiO2/meso-TiO2/CH3NH3PbI3/spiro-OMeTAD/Au were fabricated. The influence of the volume ratio of the isopropanol to water on the surface morphology, film thickness, crystal structure and bandgap of the compact TiO2 layer was investigated. The photovoltaic performance of the corresponding perovskite solar cells was compared. The PbI2 thin films were prepared by the close-spaced vacuum thermal evaporation method using the PbI2 powder as a source and subsequently treated with the CH3NH3I vapor to obtain CH3NH3PbI3 perovskite absorber layers. The chemical composition, crystal structure, microstructure and optical property of the PbI2 thin films prepared at different substrate temperature and the CH3NH3PbI3 thin films were analyzed. The photovoltaic performance of the fabricated solar cells with the structure of FTO/c-TiO2/CH3NH3PbI3/spiro-OMeTAD/Au was estimated. Moreover, the PbCl2 powders were dispersed into the isopropanol dispersions of nano-TiO2 by the ball-milling approach and then spin-coated on the compact TiO2 layers to obtain the scaffold layers containing the PbCl2. Treating the as-deposited thin films with the CH3NH3I vapor to prepare the perovskite absorber layers and the chemical composition, crystal structure and microstructure of the thin films were investigated.The results revealed that the TiO2 thin films can be successfully prepared by hydrolyzing of the metastable TiCl4 isopropanol/water solution at 130℃ and served as an efficient compact layer in perovskite solar cells. A short-circut current density (Jsc) of 22.48 mA·cm-2, an open-circuit voltage (Voc) of 865 mV and a fill factor (FF) of 54.62%, corresponding to the photovoltaic conversion efficiency (η) of 10.61% was achieved by the perovskite solar cell with the compact TiO2 layer prepared using the aqueous solution of 2 mol·L-1 TiCl4 diluted in isopropanol at 2:6 by volume as precursor solution. The PbI2 thin films with the structure of hexagnol and a preferred orientation along (006) plane were prepared by close-spaced vacuum thermal evaporation with the 480℃ source temperature and the 200℃ substrate temperature. CH3NH3PbI3 thin film with the graininess structure was obtained by treating the PbI2 thin film in the CH3NH3I vapor. The assembled solar cell gave a Jsc of 18.42 mA cm-2, a Voc of 1.06 V, a FF of 36.44% and η of 5.73%. PbI2 thin films with the bilayer structure can be deposited at the 490℃ source temperature without heating the substrate by close-spaced vacuum thermal evaporation. Treating PbI2 thin films with the CH3NH3I vapor can obtain the CH3NE3PbI3 thin films with bilayer structure and a Jsc of 21.00 mA cm-2, a Voc of 896 mV, a FF of 50.01% and η of 9.41% was achieved by the corresponding perovskite solar cell. The PbCl2 in scaffold layers can convert into CH3NH3PbI3 when it was treated in CH3NH3I vapor. In this procedure, CH3NH3PbCl3 was generated in the beginning stage, the Cl element was gradually substituted by I element with the increase of the treatment time, and finally, the CH3NH3PbI3 thin film with good crystallite were obtained.