Crystallization Kinetics Controlling And Defects Suppression In Metal Halide Perovskite Materials

With the development of metal halide perovskite materials and their applications,opmtimization of the crystallization in perovskite has attracted many attentions in recent years.However,basing on the fact that matal halide perovskite is a kind of ionic crystal materials,a wave number of pinholes and defects appear during the crystallization process.Such pinholes and defects will probably suppress the carrier transport,diffusion length and lifetime inside the materials,which hinder the improvement of the performance in applications..Aiming at eliminating the defects distributed on the surface of perovskite,effective post-passivation,basing on the electrostatic force,is developed.Nevertheless,deep-level defects,such as interstitial,Vacancies and antisite defects inside the perovskite,are formed along with the growth of the crystals.Thus,appropriate strategies in controlling the crystal growth are needed to achieve high-quaility metal halide perovskite crystals.Therefore,this paper focuses on the optimization and regulation in controlling the crystallization process of the metal halide perovskite to achieve high-performance perovskite crystal films.The main achievements are shown as followings:1.Synthesize of smooth,uniform and pinhole-free bismush based perovskite films.In this work,acetonitrile and rich-cation solution environment are used to induce the possible Bi-ACN compound.Along with the broken of coordination between Bi and ACN,the rich Cs⁺envrioment ensure the quickly and homogeneous formation of the perovskite.Depending on such strategy,uniform,smooth and pinhole-free bismuth-based perovskite films are fabricated with an average grain size of 120nm.These results prove that the appropriate selections of lewis base solvent and ion concentration can facilitate the growth of low dimensional lead-free perovskite crystals.Large on/off ratio of 10³,10⁴s endurance and over 150 times retention performances are achieved in the deivces based on the synthesized perovskite films.Moreover,the device keeps its original performance after over 2 months storage in high humidity ambient conditions.2.A ‘precursor to perovskite-like template to perovskite’（PPP）strategy is developed for the first time to optimize the crystallization of the（FAPb I₃）_x（MAPb I₃）_yperovskite fabricated in two-step method.By introducing MAAc or Gua Cl additives,the pre-formed perovskite-like intermediate phase,instead of the simple Pb-I compound,could help to optimize the crystallization Via decreasing the phase-transition energy barrier.The formed perovskite films have better orientation in the crystals,much lower defect densities and non-radiative recombination.Basing on this strategy,the fabricated perovskite solar cells showed improved fill factor of 81.5%and 79.4%with enhanced power conversion efficiency of 22.3%and 22.8%,respectively,compared to the controls.3.Development of the simultaneous crystallization control and interfical passivation basing on small molecule of ammonium salt.By introducing the BGCl as a modification layer on Sn O₂ substrate,effective suppression in formation of the bottom defects and facilitated carrier extraction at the interface are achieved in devices.The BGCl can bond to the Sn O₂ thorugh lewis coordination and electrostatic coupling.Besides,the amidogen inside BGCl can anchor the bottom iodide ions of the perovskite via hydrogen bond.Through such strategy,the defects induced non-radiative recombinations at the interface between Sn O₂ and perovskite is suppressed,the lattice strain at the bottom of perovskite is released and the carrier extraction and transport are enhanced.The fabricated perovskite solar cells show 1.19V open-circuit Voltage and82.7%fill factor.By further optimizing the ion concentration in precursor solution of the perovskite,a highest and certified 24.4%PCE is achieved,which is the highest performance sor far in the FAMA-mixed perovskite solar cells fabricated by two-step method.