Study Of The Structure Optimization And Mechanism Of Mesoporous Perovskite Solar Cells

In the organic/inorganic hybrid perovskite solar cells, the porousTiO2layer plays an important role for transporting electrons，at the same time thethickness of TiO2porous layer also affects the surface coverage of the perovskitephotosensitive layer. Therefore, the thickness of TiO2porous layer of perovskite solarcells is a worthy problem. In this paper, perovskite photosensitive layer is made by themethod of spin coating and immersion. In this method, The concentration ofPbI2solution has an great influence on the thickness and the surface coverage ofthe perovskite photosensitive layer.Therefore, the concentration of PbI2solution isalso a worthy problem in fabricating perovskite solar cells. The main contents of thisthesis as follows:1. The effect of the thickness of TiO2porous layer is studied. The deviceperformance is characterized by current-voltage (I-V) and external quantum efficiency(EQE).With the increase of the thickness of TiO2film, the photocurrent increase, andthe photovoltage decrease. The different thicknesses of porous TiO2layer andthe surface coverage of perovskite photosensitive layer are measured by SEM. Withthe increase of the thickness of TiO2film, the surface coverage of perovskite filmdecreases. The absorption intensity of perovskite photosensitive layer is measured byUV-Vis spectrum. With the increase of the thickness of TiO2film, the absorptionintensity enhances.The carrier decay lifetime of perovskite solar cells is measured bytransient photovoltage decay. When TiO2layer is too thick, the TiO2/CH3NH3PbI3interface becomes large, and facilitates the photovoltage transient process. On thecontrary, too thin TiO2film leads to a thick perovskite capping layer, which facilitatesthe recombination process in the perovskite film and results in a fast photovoltagetransient process too. Transient photocurrent decay is used to measure the transport of carriers in the perovskite solar cell. When TiO2layer is too thick, the large transportdistance of electrons need a relative long transport time. On the contrary, too thin TiO2film leads to a thick perovskite capping layer, which blocks the hole transport processand results in a relative long transport time too.In the optimized condition, the perovskite solar cell is made by the TiO2paste of1:5.5(the thickness of porous TiO2layer is206nm), which has a photoelectricconversion efficiency of14.8%with the open circuit voltage (Voc) of0.97V, the shortcircuit current (Isc) of23.1mA cm-2and the fill factor(FF) of0.66. In this device, thelifetime of photovoltage decay is1.71ms, and the lifetime of photocurrent decay is60.0s.2. The effect of the concentration of PbI2solution is studied. The deviceperformance is characterized by current-voltage (I-V) and external quantumefficiency(EQE). PbI2concentration to the effect of photovoltage is very small, butgreat influence on photocurrent. The condition of the surface coverageto perovskite photosensitive layer are measured by SEM. With the increase of theconcentration of PbI2solution, the proportion of the surface coverage to theperovskite increases. The absorption intensity of perovskite photosensitive layer ismade by different concentration of PbI2solution is measured by UV-Vis spectrum.The concentration of PbI2solution high, the proportion of the surface coverage isgood. The carrier decay lifetime of perovskite solar cells of different concentration ofPbI2solution is measured by transient photovoltage decay. When the concentration ofPbI2solution too high, the CH3NH3PbI3film becomes thick, which facilitates therecombination process, and facilitates the photovoltage transient process. On thecontrary, too slow the concentration of PbI2solution the CH3NH3PbI3is notcompletely covered with TiO2film, make the OMeTAD and TiO2contact, leakage,composite big, results in a fast photovoltage transient process too. Transientphotocurrent decay is used to measure the transport of carriers in the perovskite solarcell. When the concentration of PbI2solution too high, the CH3NH3PbI3film thick,need a relative long transport time. On the contrary, too slow the concentration of PbI2 solution, the CH3NH3PbI3less, results in a relative long transport time too.In the optimized condition, the perovskite solar cell is made by the PbI2solutionconcentration of462mg/ml, which has a photoelectric conversion efficiency of13.4%with the open circuit voltage(Voc) of0.99V,the short circuit current (Isc) of22.9mAcm-2and the fill factor(FF) of66.05. In this device,the lifetime of photovoltage decayis2.83ms, and the lifetime of photocurrent decay is44.5s.