| Inorganic-organic perovskite solar cells(PSCs)have been developing rapidly since 2009 due to their high power conversion efficiency(PCE),solution processibility and bipolar transmission characteristics.Methylamine lead iodide(CH3NH3PbI3)is one of the most used active materials in PSCs.The micro-morphology,crystallization and phase purity of CH3NH3PbI3 thin films directly determine the PSCs' efficiency.Target of this thesis is to accelerate perovskite conversion,improve its morphology and grain size,and thereby further enhance device performance.By modifying PbI2 film morphology and controlling perovskite conversion reaction conditions,high-quality CH3NH3PbI3 thin films and high-efficiency PSCs were obtained.The main contents and results are as follows:(1)A simple and effective approach to the fast preparation of perovskite films for high-performance perovskite solar cells via solvent coordination and anti-solvent extraction(SCAE)was developed.When the conventional sequential deposition method is applied to fabricate PSCs,inefficient conversionof PbI2 to perovskite has been a big challenge.In the work,porous PbI2 films were obtained via the SCAE method instead of compact Pb I2 films via the conventional thermal annealing.Perovskite with high phase purity and uniform morphology can be rapidly converted from the porous Pb I2 film with the assistance of its micro/nano-structured interface.It is demonstrated that Pb I2·DMSO(dimethyl sulfoxide,coordinated solvent)intermediate complexes are not only capable of restricting the fast growth of PbI2 grains,but also capable of facilitating the formation and regulation of porous PbI2 structures during the process of anti-solvent(chlorobenzene)extraction.The porosity of Pb I2 films increases with the prolongation of chlorobenzene loading time.With the porous PbI2 template,its complete conversion time into CH3NH3PbI3 was greatly shortened to less than ten minutes from one hour for the conventional method.Moreover,for the devices fabricated with the conventional method,the PCE was only around 10.6 % due to their poor perovskite film morphology.The SCAE-treated PbI2 films(chlorobenzene loading time was zero)converted to perovskite completely within around 8 min.When the chlorobenzene loading time was further extended to 10 s and 20 s,the conversion time was shortened to5 min and 1 min,respectively.The average efficiencies of the PSCs derived from the PbI2 films with chlorobenzene loading time of 0,10 s and 20 s were11.3 %,14.5 % and 13.1 %,respectively.The best device exhibits a PCE of15.66 % in the reverse scan direction,and a PCE of 14.02 % in the forward scan direction,which can be ascribed to its uniform surface morphology and moreefficient carrier transfer at the interfaces.(2)The porous PbI2 films obtained via SCAE was used to prepare perovskite films by a “solid-solid” interdiffusion reaction to further improve perovksite morphology and grain size,and thereby enhance device performance.It is demonstrated that the porous structure of PbI2 films obtained via SCAE can facilitate the conversion of perovskite during the process of interdiffusion reaction.Moreover,the obtained perovskite films have better surface morphology and higher crystallinity than those prepared by the conventional interdiffusion method,which greatly enhanced the Jsc and FF of the cells.The average efficiency of the device increased from 10.9 % to 12.6 %.The thickness and morphology of the perovskite active layer was further optimized by adjusting the concentration of PbI2 and CH3NH3 I solutions and chlorobenzene loading time.The results show that the perovskite film is optimal when a 550mg/ml Pb I2 solution,a 65 mg/ml CH3NH3 I solution and the chlorobenzene loading time of 10 s are employed.The best device fabricated exhibits a PCE of16.5 % in the reverse scan direction and a PCE of 15.2 % in the forward scan direction. |
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