Regulation Of High-Quality Perovskite Films And Photovoltaic Cells Performance

Finding clean renewable energy to replace traditional fossil fuel is critical for mitigating energy crisis and reducing environmental pollution.Solar cells that convert energy of sunlight into electricity offer a viable route for solving this issue.In recent years,perovskite solar cells(PSCs)have gained increasing attention from academic and industrial fields due to its advantages of extremely low preparation cost and rapid development of photoelectric conversion efficiency(PCE).How to further achieve breakthroughs in device performance and accelerate the commercialization of PSCs,there are still many scientific problems.As the core functional layer of PSCs,the crystal quality of perovskite films determines the final device performance.In addition,PSCs is a multilayer film structure device,and the interface properties are closely related to the transport kinetics of photogenerated carriers,which have an important impact on the device performance.Based on this,this study focused on the preparation of high-quality perovskite films and interface design.By means of intermediate phase engineering,additive engineering,phase transition engineering and interface engineering,the surface morphology,crystal orientation,strain,defect states and interface energy level arrangement of perovskite films were optimized and adjusted,which minimized the energy loss of PSCs and constructed efficient and stable PSCs.The effect of intermediate phase on crystal growth and device performance before perovskite film annealing has been investigated.The perovskite films were deposited by a two-step spin coating method,and the deposition atmosphere was changed to obtain intermediate films exhibiting α and δ phases.The perovskite films obtained by annealing the intermediate films with different phase structures was compared.It was found that the perovskite films prepared by annealing theδ-phase intermediate films exhibited higher crystallinity,better crystal orientation,and larger grain size.Furthermore,combined with a series of spectroscopic characterizations,it was found that the perovskite films prepared by annealing theδ-phase intermediate films possess stronger light absorption,longer carrier lifetimes,and smaller carrier recombination probability.PSCs constructed based on the annealing of the δ-phase intermediate film achieved the highest efficiency output of 22.09%,and the unencapsulated device could still maintain the initial efficiency of 92.4%after aging in air for 1200 h.The technology of n-hydroxyacrylamide(NMA)monomer to control the crystal growth of perovskite films was developed.the effect of NMA on the crystal quality of perovskite films and device performance was systematically studied.Revealing NMA regulatory mechanism for charge transport and recombination in the device.It was found that introducing NMA monomer could lead to additional heterogeneous nucleation,lowering the nucleation free energy barrier of perovskite,thereby accelerating the growth of crystals and obtaining micron-sized perovskite films.During the thermal crystallization of perovskite films,the self-polymerization of NMA monomer could inhibit the lattice expansion of perovskite and reduce the lattice strain of perovskite films.In addition,NMA could also passivate the defects at the perovskite grain boundaries,further reducing the defect state density of perovskite films.The introducing NMA monomer effectively increases the composite resistance and built-in electric field of the device,reduces the dark current by more than an order of magnitude,which realizes the efficient charge transportation inside the device.The final PSCs achieved a PCE of 22.9%,and the device also showed excellent overall stabilityThe continuous phase transition technology(PTG,ie α→δ→α phase)was developed to process CsPbI2Br films.The effects of PTG on secondary grain growth and residual tensile strain release in CsPbI2Br films were systematically investigated.The physical mechanism which PTG improves the charge dynamics of CsPbI2Br PSCs was revealed.It was found that after PTG treatment,the crystallinity of the CsPbI2Br film was enhanced,the grain size was increased from 0.6 μm to 5.0 μm,and the residual tensile strain is effectively released by 62±4%,which effectively alleviates the lattice distortion,reduces the defect states on the surface and the whole film,and improves the optoelectronic properties and stability of the CsPbI2Br film.In addition,the recombination resistance and built-in electric field of the PTG-treated CsPb2Br PSCs were significantly increased,which effectively suppressed the non-radiative recombination of photogenerated carriers inside the device and improved the charge transfer efficiency.The efficiency of CsPbI2Br PSCs was increased from 13.4%to 16.5%,and the corresponding open circuit voltage was increased from 1.14 V to 1.36 V.Meanwhile,the device stability was also greatly improved.Aiming at the serious energy loss phenomenon in CsPbI2Br PSCs,a technique for modifying the interface between SnO2 electron transport layer/CsPbI2Br absorption layer by NH4BF4 was developed.The effects on the SnO2 electron transport layer,the crystal quality of CsPbI2Br films and the kinetics of photogenerated charges inside the device were discussed.It was found that the NH4BF4 interface regulation can reduce the surface defect density of SnO2 films,improve electron mobility and conductivity,and raise the conduction band position,thereby reducing the non-radiative recombination loss of charges at the interface and enhancing the extraction ability of electrons by SnO2 films.The highest efficiency of CsPbI2Br PSCs reached 17.09%.More importantly,the highest open circuit voltage of the device reached 1.427 V,and the energy loss is 0.493 eV,which is the minimum reported CsPbI2Br PSCs.In addition,the environmental and thermal stability of the device was also improved.