Controllable Fabrication Of High Quality Perovskite Films For High Performance Photovoltaics

Organic-inorganic hybrid perovskite is widely investigated due to its unique optoelectronic properties（long carrier lifetime,high absorption coefficient,adjustable bandgap,etc.）and low fabrication cost,wherein the power conversion efficiency（PCE）of corresponding solar cells is raised from 3.80%in 2009 to 25.70%at now.However,the poor operational stability and low efficiency of large area devices are still the major obstacles toward the commercialization of perovskite solar cells（PSCs）.Therefore,we aimed at the controllable fabrication of perovskite films,to improve the efficiency and stability of PSCs by modifying the material optoelectronic properties.Details including:（1）We developed a strategy“The synergy of non-covalent bond”to efficiently passivate halogenic anion and organic cation vacancy defects of perovskite films.We used the fluorine which shows higher electronegativity to form the stronger hydrogen bond with organic cations,as well as the stronger ionic bond with lead ions.Based on these interactions,the perovskite components could be immobilized to improve the formation energy of vacancy defects,thus the defects density were reduced and ions migration were inhibited.Finally,the fluorine incorporated PSCs exhibited 21.92%PCE and kept 90%of initial PCE after 1000 h operation.（2）We developed a new annealing process–liquid medium annealing to reproducibly fabricate high quality perovskites.The perovskite wet films were annealed in chemically stable liquid medium to obtain the films with high crystallinity and low defects density.Liquid medium could provide the more uniform thermal filed（omni-directional heating）to accelerate the perovskite growth,leading to the increased grain size of perovskite crystals.In addition,it could inhibit the loss of perovskite volatile components to keep the stoichiometry.Most importantly,liquid medium could protect the perovskite films from the destruction by ambient conditions（such as humidity）,to achieve the all-weather fabrication of perovskites.Based on the liquid medium annealing,the corresponding small area PSCs（0.08 cm²）exhibited 24.27%（certified 23.70%）PCE and kept 95%of initial PCE after 2000 h operation.Large area PSCs（1 cm²）exhibited 23.35%（certified 22.30%）PCE,which is the highest among all the reported values by third part.（3）We systematically monitored the performance evolution of PSCs based on FA_1-xCs_xPbI₃ system under different ageing conditions,and revealed the degradation mechanism of PSCs under the illumination and operation stressors.Based on the micro characterization of aged perovskites,we found that the phase separation in perovskite film was the major reason for performance loss of PSC devices.Besides,we also considered that the light induced photo carriers provided the thermodynamic driving force for the phase separation.（4）We fabricated the FA-based large area perovskite films through the two-step slot-die coating process.We fabricated mesoporous PbI₂ to promote the infiltration of organic cation,and added perovskite seeds into PbI₂ film to reduce reaction energy barrier,finally improved the conversion content from PbI₂ to perovskite and obtained high quality perovskite films.The corresponding solar cells exhibited 20.53%PCE.In addition,through the etching parameters modification,electron transport layer deposition adjustment,etc.,we fabricated the perovskite solar modules with an efficiency of 20.08%（25 cm² aperture area）.