Growth Kinetics Of Hybrid Perovskite Crystal And High Performance Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells have attracted growing attention in recent years due to their high efficiency and low fabrication cost.Hybrids perovskite materials possess unique crystal structures and electronic configurations,which results in their excellent opto-electrical properties,including high absorption coefficient,long carrier lifetime and high mobility,tunable band structure,and high tolerance of defects.We have demonstrated a novel and reproducible approach to fabricate hybrid perovskite films,by tuning the coordination capability of additives(e.g.acetonitrile).Through affecting the interaction between PbI2 and DMF,the crystallization process with distinctive nucleation and grain growth have taken place.A quick crystallization and film formation of PbI2,adequate nucleation center for MAI,and promoted CH3NH3PbI3 growth have been observed to favor the realization of superior film with large grain size.This novel protocol allows fabricating an efficient perovskite solar cell(low temperature processed ITO/Ti02/Perovskite/Spiro-OMeTAD/Au)with a PCE of 19.7%and the stabilized power output efficiency over 17.5%.The coordination capability of additives has been proven to be an effective parameter to control the grain size.The employment of weak coordination additive leads to different crystallization kinetics upon film growth,which opens a new direction on the film formation study,and provides an effective approach toward efficient and stable perovskite solar cells.It can be further extended to the fabrication of other perovskite and organic-inorganic hybrid materials based optoelectronic devices.Mixed anion/cation perovskites absorber has been recently implemented to construct highly efficient single junction solar cells and tandem devices.However,considerable efforts are still required to map the composition-property relationship of the mixed perovskites absorber,which is essential to facilitate device design.Here we report the intensive exploration of mixed-cation perovskites in their compositional space with the assistance of a rational mixture design(MD)methods.Different from the previous linear search of the cation ratios,it is found that by employing the MD methods,the ternary composition can be tuned simultaneously follow simplex lattice designs or simplex-centroid designs,which enable significantly reduced experiment/sampling size to unveil the composition-property relationship for mixed perovskite materials,and to boost the resultant device efficiency.We illustrated the composition-property relationship ofthe mixed perovskites in multi-dimension,and achieved an optimized power conversion efficiency of 20.99%in the corresponding device.Moreover,the method is demonstrated to be feasible to help adjust the bandgap through rational materials design,which can be further extended to other materials systems,not limited in polycrystalline perovskites films for photovoltaic applications only."Perovskite Seeds" improved the growth process of perovskite crystals has been developed,and the efficiency of solar cells has been further improved.The method of perovskite seeds is to pre-mix part of the A-site cation with PbI2 in the first step during deposition of the PbI2 solution.The method is interposed between two-step and one-step spin-coating methods.The perovskite seeds method ensure the uniformity of the film composition and the rapid crystal growth process.By comparing the effect of different seed components on the efficiency of perovskite solar cells,it was found that perovskite seed crystals based on wide bandgap can achieve higher efficiency than narrow bandgap perovskite seeds.In addition,compared with the traditional two-step spin coating deposition method,the perovskite seeds method can make the film reaction more fully,reduce the residual lead iodide content,and can adjust the bandgap of the film.Finally,perovskite seeds method fabricating an efficient perovskite solar cell with a PCE of 21.5%.Here,a facile,two-step consecutive deposition method was developed for the first time to grow a quasi-2D/3D perovskite hierarchical superstructure,with oriented quasi-2D((BA)2(MA)m-1PbnI3n+1)perovskite nanosheet(NS)perpendicular aligned on n≈∞ perovskites.The perovskite superstructure are found to be the mixture of multiple perovskite phases,with n = 2,3,4 and 3D Perovskite,however,the n value was naturally increased from top to the bottom that is distinct from most of recent reports.The growth thermodynamics and the carrier dynamics of the quasi-2D/3D perovskite superstructures were thoroughly revealed based on the analysis of the structural,morphological,optoelectronic behavior evolution upon varying the growth condition.Therein,the significant findings are presented as follows:A facile,two-step consecutive deposition method was developed for the first time to grow a quasi-2D/3D perovskite hierarchical superstructure,with oriented quasi-2D((BA)2(MA)n-1PbnI3n+1)perovskite nanosheet(NS)perpendicular aligned on n ≈∞ perovskites.Distinct from most of the other quasi-2D perovskite film obtained by one-step solution process,the present((BA)2(MA)n-1PbnI3n+1)perovskite materials are composed of multiple phase with n value naturally increasing from top to the bottom.We thoroughly studied the crystallization mechanism and revealed that both the initial ratio of BAI/MAI and the corresponding concentration,collectively contributing the spatially confined nucleation and growth of oriented quasi-2D superstructure perovskite on 3D perovskites.The growth mechanism of the oriented quasi-2D/3D perovskite superstructures was found to be similar to the mechanism of dendritic growth.Additionally,we have identified an efficient charge carrier transfer within the perovskite superstructure,indicating a unique type of energy funnel with photoexcitation transferring from top surface to the bottom.The hierarchical quasi-2D/3D perovskite film was successfully used to fabricate photodetectors with a responsivity surpassing 10,which is one of high responsivity among perovskite photodetectors.Overall,this work represents a significant step to exquisite control of perovskite hierarchical structure,which may benefit the fundamental understanding of perovskite growth and its application in photovoltaics and other optoelectronics devices.