Preparation Of Perovskite Absorber Layer By Vapor-assisted Solution Process And The Photovoltaic Performance Of Solar Cells

In this thesis, the mixed solution of PbI2 and PbCl2 in DMF as precursor solution were spin-coated to prepare lead halide thin film. These lead halide thin films were transformed to perovskite thin films by CH3NH3I vapor, and the planar perovskite solar cells with the architecture of FTO/c-TiO2/CH3NH3PbI3-xClx/spiro-OMeTAD/Au were fabricated. The influence of the PbCl2 content in lead halide thin film on the chemical composition, crystal phase, morphology and optical absorption of perovskite thin film was investigated. The photovoltaic performance of the corresponding perovskite solar cells was compared. The CH3NH3PbI3-xClx thin film was prepared via vapor-assisted solution process, and the chemical composition, crystal structure, microstructure and optical property of the CH3NH3PbI3-xClx thin film at different CH3NH3I vapor conversion temperature and time were analyzed. Moreover, the CH3NH3PbI3-xBrx thin film was obtained by vapor-assisted solution process, and element Br was doped via annealing in CH3NH3Br vapor and dipping in CH3NH3Br solution of isopropanol. The chemical composition, crystal structure, microstructure and optical property of the CH3NH3PbI3-xBrx thin film prepared by various doping methods were discussed.The results revealed that the concentration of Pb in the precursor solution increased by adding different content of PbCl2 powder to PbI2 solution of DMF. EDS results show that element Cl successfully doped to obtain CH3NH3PbI3-xClx thin film. The 300 nm-thick CH3NH3PbI3-xClx thin film with the precursor solution of 0.8M PbI2 and 0.2M PbCl2 in DMF served as an efficient absorption layer in perovskite solar cells and performed best photovoltaic property. A short-circut current density (Jsc) of 15.70 mA·cm-2, an open-circuit voltage (Voc) of 930 mV and a fill factor (FF) of 69%, corresponding to the photovoltaic conversion efficiency (η) of 10.12%was achieved by the corresponding perovskite solar cell. Under atmospheric pressure, the lead halide thin film can be successfully transformed to CH3NH3PbI3-xClx thin film at CH3NH3I vapor conversion temperature of 130 ℃. The XRD result exhibited that the crystallinity of CH3NH3PbI3-xClx thin film with CH3NH3I vapor conversion temperature of 130 ℃ was higher than that of 140 ℃ and 150 ℃. The planar perovskite solar cell based on the treatment of CH3NH3I vapor at 130 ℃ exhibited the highest η of 12.62%along with a Jsc of 17.79 mA·cm-2, an Voc of 0.98 V, a FF of 0.73 and an average η of 12.13±0.49%.The mixed lead halide thin film can be transformed to CH3NH3PbI3-xClx thin film by CH3NH3I vapor at 130 ℃ with the corresponding conversion time of 200 min,260 min,320 min. The crystallinity of CH3NH3PbI3-xClx thin film with 320 min was higher than that of 200 min and 260 min. With the increase of the conversion time, the grain size of perovskite crystallites increased and the corresponding boundaries decreased. The planar perovskite solar cell based on the conversion time of 200 min exhibited the highest PCE of 12.62% with Jsc of 17.79 mA·cm-2, Voc of 980 mV and FF of 72.75%. Element Br can be successfully doped by annealing in CH3NH3Br vapor and dipping in CH3NH3Br solution of isopropanol to obtain CH3NH3PbI3-xBrx thin film. There was no obvious difference in thickness between perovskite with doping Br and without doping Br. Vapor-assisted solution process and annealing in CH3NH3Br vapor can obtain full coverage, compact and high-quality CH3NH3PbI3 thin film and CH3NH3PbI3-xBrx thin film, while the CH3NH3PbI3-xBrx thin film with dipping in CH3NH3Br solution of isopropanol was porous. Treating CH3NH3PI3 thin film with annealing in CH3NH3Br vapor can obtain CH3NH3PbI3-xBrx thin film and a Jsc of 16.46 mA cm-2, a Voc of 1010 mV, a FF of 75.84%and η of 12.59%was achieved by the corresponding perovskite solar cell.