| In recent years,organic metal halide perovskite solar cells have made considerable progress in the photovoltaic field with the maximum certified power conversion efficiency(PCE)of 25.5%.However,most of perovskite solar cells are fabricated by lead-based perovskites,which is extremely harmful to the environment and the human body and limits their practical application.Using environmentally friendly tin instead of lead to prepare tin-based perovskite solar cells is an ideal solution to the problem of lead toxicity,but the PCE of tin-based perovskite solar cells is still low,one of the main reasons is the rapid and disordered crystallization process of tin-based perovskite results in low-quality films.Polar environment,growth substrate and other factors have a greater influence on the crystallization process of tin-based perovskites.In order to control the crystallization process of tin-based perovskite to prepare high-quality films,the following research is carried out in this paper:(1)Low-dimensional tin-based perovskite is introduced at the interface between FASnI3perovskite and PEDOT:PSS by the mean of propyl iodide amine(PAI)pretreatment,which induces the preferred vertical growth orientation and increases the crystallinity of FASnI3 perovskite film.Benefit from PAI pretreatment,the grain size is increased from 550 nm to 740 nm,and the morphology of the FASnI3perovskite film is improved.In addition,the low-dimensional tin-based perovskite passivated the defects on the bottom surface of FASnI3 perovskite film,and the density of defect states decreased from 7.44×1016 cm-3 to 4.10×1016 cm-3.The PCE of FASnI3 perovskite solar cell prepared by PAI pretreatment increased from 5.6%to 7.8%,and the fill factor increased from0.58 to 0.68.(2)The crystallization process of FASnI3 perovskite is controlled by constructing a PEDOT:PSS-Vanadium oxide(VOx)mixed hole transport layer and preparing FASnI3 perovskite film based on it.The mixed hole transport layer increases the number of nucleation sites during the crystallization process,and prepares a dense and non-porous high-quality FASnI3 perovskite film.Vanadium ions partially enter the perovskite grain boundaries through spin coating and annealing to passivate the defects at the grain boundaries,and the defect state density of FASnI3 perovskite is reduced from6.98×1016 cm-3 to 5.01×1016 cm-3.In addition,the PEDOT:PSS-VOx mixed hole transport layer reduces the energy barrier with FASnI3 perovskite and the energy loss during carrier transmission,and improves the carrier transport efficiency.Finally,the PCE of device is increased from 5.8% to 8.0%.(3)In the spin coating stage of FASnI3 tin-based perovskite,an ethyl acetate vapor atmosphere is constructed to control the crystallization process of FASnI3,which promotes the precipitation of nucleation sites and delay the subsequent crystal growth process.High-quality FASnI3 perovskite films with micron-level grain size,preferred orientation and no holes is prepared by this method.Benefit from improved film quality,the defect state density of perovskite is reduced from 1.38×1017cm-3 to 8.51×1016 cm-3,which suppresses the non-radiative recombination caused by defect trapping carriers.The PCE of FASnI3perovskite solar cells prepared by this method is increased from 6.3%to10.1%,and the open circuit voltage(Voc)is increased from 0.45 V to 0.62 V,without obvious hysteresis.In addition,the stability of the device is also enhanced. |
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