Low-defect Perovskite Film Fabrication And Highly Efficient And Stable Solar Cells

Up to now,perovskite solar cell has become a bright star in the field of photovoltaic,which is sought after by scientific research workers.To make it the main force of commercialization,however,there are still some of the key issues that need to be broken,such as large-area devices fabrication,stability of devices,development of inorganic non-lead material systems,etc.In view of the above problems,we systematically explored high performance planar heterojunction perovskite solar cell（PSCs）with the customization of device components,the preparation of high-quality perovskite film and the problem of inorganic perovskite film formation.The main contents are as follows:For the first time,we systematically investigate band offset between ETL and perovskite absorber by tuning F doping level in SnO₂ nanocrystal for n-i-p planar PSCs.We find that gradual substitution of F^-into the SnO₂ ETL can effectively reduce the band offset and result in a substantial increase in device V_OC.In improved V_OC of PSCs can be attributed to the tailored Fermi energy of ETLs forming well-matched energy levels with perovskite while reducing up of the electron concentration and the rate constant for interfacial carrier recombination.In addition,we introduced bi-layer ETLs in efficient n-i-p planar PSCs,bi-layer ETLs with different carrier concentration enhances the built-in electric field of the device and accelerates the transmission and extraction of photo-excited carrier,and thus achieving 20.2%PCE with improved cell stability.A bifunctional metal ion Ni²⁺was introduced to enhance grain size and defect passivation through using a method of controllable two-step sequential deposition perovskite films.The addition of Ni²⁺can induce a polyporous PbI₂ films due to different solubility between NiCl₂ and PbI₂ which benefits penetration of MAI ions and thus formation of large-grain-sized perovskite films eventually.The Ni²⁺ions insert into the interstices of the MAPbI₃ lattice can reinforce the interplay of MA cation and octahedral[PbI₆]^4–,restraining the generating of Pb⁰.Meanwhile,the interaction of the Ni²⁺ions and PbI₃^-antisites defects could further passivate defects at the grain boundary surfaces after completion of perovskite growth.Accordingly,an improved power conversion efficiency of20.61%can be achieved for the Ni²⁺addition-based PSCs with enhanced cell stability under ambient conditions.This chapter proposes black-phosphorus quantum dots（BPQDs）as effective seed-like sites to modulate the nucleation and growth of perovskite crystals in planar perovskite（CsPbI₂Br）solar cells.A small amount of dispersed BPQDs which were to induce strong chemical binding between molecules of CsPbI₂Br precursor and phosphorus ions through relief Coulombic repulsion of BPQDs’s lone-pair electrons.Through this intermixing-seeded growth technique and chemical bonding effect,α-phase BPQDs@CsPbI₂Br hybrid films with substantial morphological improvements,such as increased enhanced coverage and uniformity,was realized,and the epitaxial growth of CsPbI₂Br matrix on BPQDs surfaces passivated the easily oxidized BPQDs as well.The strong interaction of the structure of BPQDs/CsPbI₂Br core–shell reinforces a stable CsPbI₂Br crystallite,and improves electron-extracting efficiency,and the corresponding devices exhibits a promising PCE of 15.47%and excellent moisture stability.Moreover,we discover through in situ XRD measurements that CsPbI₂Br suffer three phase transitions during annealing process,and has made the corresponding elaboration and discussion.Confronting above research,the photogenerated charge behavior has been carefully probed to illustrate the device working mechanism by using electrochemical impedance spectra,Kelvin probe force microscopy（KPFM）,capacitance-voltage（C-V）analysis,and Mott-schottky curve.Meanwhile,the orientation,nucleation,and growth process of the perovskite film crystals were monitored by two-dimensional X-ray diffraction,fluorescence microscopy,and transmission electron microscopy.The effect of perovskite film quality and interface carrier transport on PSCs device performance has been carefully expatiated based on a large number of experiments and theoretical research.