| Due to the depletion of traditional energy such as coal,people have been trying to find clean renewable energy.In recent years,solar cells using perovskite as light-absorbing material have attracted extensive attention of researchers.Perovskite materials are widely used in OLED,semiconductor film,catalysis,and other fields because of their suitable bandgap,good optical absorption coefficient and excellent carrier mobility.However,their low stability limits the improvement of conversion efficiency.In this paper,with the help of density functional theory calculations,the cation doping method and the organic molecular passivation method to improve the stability of perovskite materials are deeply studied.This paper not only explores the internal mechanism of cation doping,but also creatively explores the optimal proportion of cation doping,and puts forward the double anchor passivation strategy of passivation molecules.The main research contents and conclusions of this paper are as follows:(1)Based on the first principle calculation,we selected the best MAPbI3 dopant from a variety of organic cations and further revealed the mechanism of cation doping to improve stability.Our results show that large-sized cations(similar to IPA+,TriMA+,and GA+)can bring an enhancement of defect formation energy and migration barrier to the system,thereby effectively inhibiting the formation and diffusion of structural defects.We also reveal the internal mechanism of improving the structural stability from two aspects of structural deformation and hydrogen bond formation.First,the lattice distortion caused by the doping of large-scale ions hinders the movement of I ions and MA ions in the crystal.Furthermore,the number of hydrogen bonds formed between I ions and organic cations in the distorted lattice is significantly increased,which effectively improves the stability of the perovskite structure.(2)From the perspectives of defect energy,electronic structure,light absorption coefficient,etc.,we systematically studied the optimal concentration in the cation doping method,and briefly analyzed its mechanism.We found that low concentration doping makes the perovskite system have an appropriate bandgap,higher defect formation energy and higher light absorption peak.In addition,the low-concentration partial doping of perovskite can also stabilize the tolerance factor in a more suitable range.Therefore,we suggest that the optimal doping ratio of cations is 3.2%-12.5%.Low-concentration doping can improve the structural stability through small lattice distortion,while an excessively large doping ratio can cause phase separation of perovskite and result in loss of battery performance.(3)We systematically studied the double anchoring passivation effect of passivation molecules on perovskite materials,and discussed the passivation mechanism of MP,D4TBP and tryptophan.Both ends of the MP molecule can form coordination bonds with unsaturated lead atoms respectively to realize the passivation of Pb-N and Pb-O modes.D4TBP can achieve passivation of Pb-O coordination bonds by virtue of its carboxyl group,and its amino group can occupy the cationic site in MAPbI3 to achieve the passivation of A-site defects.The tryptophan molecule has both carboxyl and amino groups,so two passivation modes of Pb-N and Pb-O can also be achieved.In addition,we also propose the concept of hydrogen bond passivation through the analysis of passivating molecules and inorganic lattice sites.Since these organic molecules can achieve two modes of passivation,we also call them double-anchored passivation molecules. |
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