| Perovskite solar cells(PSCs)have become the focus of research in the past decade due to their excellent power conversion efficiency(PCE)and low production cost.However,currently reported PSCs with high performance are prepared with lead-based materials,and its stability is not ideal,which restrict the large-scale industrial application of PSCs.In this paper,metallic element strontium(Sr)substituted organic-inorganic hybrid materials were prepared for lead-less PSCs.The effect of Sr substitution on perovskite materials and PSCs performance were systematically investigated,the corresponding microscopic mechanisms were clarified,and the cells stability were also discussed.By using antisolvent-assisted single step method and two-step spin-coating method,part of lead iodide(PbI2)were replaced with strontium iodide(SrI2)in the precursor solution to prepare Pb-less perovskite films and fabricate the mesoporous PSCs.The influence of Sr substitution on the film formation and photovoltaic property of perovskites was illuminated by scanning electron microscope(SEM),X-ray diffraction(XRD)and time-resolved photoluminescence(TRPL)analyses.The results show that,in the antisolvent-assisted single step method,Sr substitution has an impact on the formation of intermediate phase,resulting in a lower coverage and an increased defect density of perovskite films.When Sr content rises from 0 to 5 mol%,the device's power conversion efficiency(PCE)decreases from 15.22%to 6.37%.In two-step spin-coating method,a moderate amount of SrI2 can change the chemical component of PbI2 precursor,resulting in a less PbI2 remnant and a decreased defect density in perovskite films.When Sr content is 10 mol%in the PbI2 solution,the solar cell exhibits a considerable PCE of 15.52%under AM 1.5G solar illumination.Moreover,strontium chloride(SrCl2)substituted lead-less PSCs were constructed successfully,and the effect of Sr substitution on the perovskite film formation and its photovoltaic property was investigated in detail by XRD,SEM,UV-visible absorption,TRPL,X-ray photoelectron spectroscopy(XPS)and electrochemical impedance spectroscopy(EIS)analyses.It is demonstrated that the introduction of Sr substitution changes the chemical composition of PbI2 precursors and reduces the excess PbI2 in the perovskite films.A 10 mol%SrCl2 substitution in the PbI2 precursor solution can increase the absorbance of the resultant perovskite film and enhance the electron extraction at the "perovskite/TiO2" interface,thus increasing the device's short-circuit current density(Jsc)from 17.41 mA cm-2 to 17.45 mA cm-2.At the same time,Sr substitution can reduce the charge combination in the PSC,which allows the PSC to obtain a higher open-circuit voltage(Voc)of 1.08 V and fill factor(FF)of 0.74.Finally,the PSC prepared with 10 mol%Sr substitution exhibits a considerable power conversion efficiency(PCE)of 15.64%,showing an improvement of 18.9%compared to that of the pristine device.In addition,by using a two-step spin-coating method,10 mol%SrI2 and 10 mol%SrCl2 substituted perovskite films were synthesized and utilized for assembling mesoporous PSCs.The influence of Sr substitution on the humidity and thermal stability of PSCs were systematically investigated by various characterization methods.It is indicated that the 10 mol%SrCl2 substitution can improve the humidity resistance of perovskite films,which is conducive to inhibiting the increase of perovskite defect concentration caused by humidity.After storing at 200±5?,30±5%RH for 21 days,the 10 mol%SrCl2 substituted PSC can still maintain 84%of the initial efficiency.However,the 10 mol%SrI2 substituted PSC exhibits a strong humidity sensitivity,which results in the increase of series resistance and the decrease of recombination impedance,thus leading to PCE of the PSC keeps less than 20%of the initial value after storing at 20±5?,30±5%RH for 21 d.As for the thermal stability of PSCs,the 10 mol%SrI2 and 10 mol%SrCl2 substituted perovskite films exhibit a certain thermal resistance.After 18 thermal cycles,the two PSCs can maintain over 90%of the initial PCEs... |
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