Preparation Of Perovskite Thin Films And The Photovoltaic Performance Of TiO₂ Nanorod Array Solar Cells

Organometallic halide perovskite materials have the characteristics of high absorption coefficient,long carrier diffusion length,broad band light absorption and high tolerance of impurities and defects,and photoelectric conversion efficiency(PCE)of the corresponding solar cells has increased dramatically from 3.8%in 2009 to a certified 22.1%in 2017,it has become one of the hot topics in academic research.Perovskite thin film is one of the main components of the perovskite solar cell,which has a great influence on the photovoltaic performance.In this thesis,the main strategy is to improve the solubility of PbI2 powder in DMF by the formation of the PbI2·DMSO complex to obtain the high-concentration PbI2·DMSO complex precursor solutions,and prepare the high-thickness perovskite thin films.The high-thickness perovskite thin films can directly enhance the absorbance of visible light,Br-doping can improve the diffusion length of electrons and holes,the introduction of short-length,small-diameter,high areal density TiO2 nanorod array can improve the charge separation and electron transportation in the interface of perovskite/TiO2-The high-thickness,large-grain,Br-doping perovskite thin films are successfully prepared by improving the annealing temperature and optimizing the CH3NH3Br content in the CH3NH3I and CH3NH3Br mixture solutions in the two-step solution method.The influence of PbI2 DMSO complex precursor solution concentration,CH3NH3I and CH3NH3Br mixture solution chemical composition,annealing temperature and annealing time,the TiO2 nanorod array microstructure on the chemical composition,crystal phase,microstructure and optical absorption of perovskite thin films are systemically investigated and the photovoltaic performance of the corresponding TiO2 nanorod array perovskite solar cells is compared.The results reveal that the PbI2·DMSO complex precursor solution concentration in DMF can reach 1.7 mol· dm-3 by the formation of the PbI2 DMSO complex at room temperature.The 660 nm,600 nm and 530 nm thick perovskite thin films are prepared by converting 1.7 mol·dm-3,1.5 mol·dm-3,1.3 mol·dm-3 PbI2·DMSO complex precursor solutions using high concentration(0.465 mol dm-3)CH3NH3I and CH3NH3Br mixture solution,and the corresponding TiO2 nanorod array perovskite solar cells present the best PCE of 15.56%,13.89%and 11.80%,and the average PCE of 14.93±0.63%,12.45 ± 1.44%and 10.77 ± 2.03%at the relative humidity of 50%?54%.When the annealing temperature of the perovskite thin films which are prepared by converting the 1.7 mol·dm-3 PbI2·DMSO complex precursor solution increase from 100 ? to to 120 ? and 140 ?,the optimum annealing time decrease from 40 min to 20 min and 10 min,the peak intensities of the corresponding perovskite at 2?= 14.05° gradually strengthen from 3649 to 4280 and 4720,and the grain sizes increase from 200?300 nm to 300?500 nm and 500?800 nm.The results present that the TiO2 nanorod array perovskite solar cells at the annealing temperature and time of 140 ? and 10 min exhibit the best PCE of 16.11%and the average PCE of 15.62 ± 0.49%.The CH3NH3I and CH3NH3Br mixture solutions with the CH3NH3Br content of 0%,5%,10%,15%and 20%are prepared.The Br contents in the perovskite thin films which are prepared by converting the 1.7 mol·dm-3 PbI2·DMSO complex precursor solution and at the annealing temperature and time of 140 ? and 10 min increase linearly with the increase of CH3NH3Br contents in the CH3NH3I and CH3NH3Br mixture solutions,and the rate of increase of Br contents in perovskite thin films is less than that in the CH3NH3I and CH3NH3Br mixture solutions.With the increase of Br content in perovskite thin films,the main diffraction peaks of(110)planes shift towards the higher 2? degree,and the absorption band-edges of the corresponding perovskite thin films gradually shift towards shorter wavelengths.And it is worth noting that the perovskite thin films using CH3NH3I and CH3NH3Br mixture solutions with 5%CH3NH3Br possess higher crystallinity and more uniform grain size,the corresponding TiO2 nanorod array perovskite solar cells achieve the best PCE of 16.47%,and the average PCE of 16.06± 0.52%.