Research On The Structure Stability And Device Performance Of Cesium Lead Iodide Perovskite Thin Film

Recently,inorganic perovskite CsPbI3 due to the well thermal and component stability received much attention.However,the size-unmatchable Cs ions usually result in the phase transition from perovskite structure to the non-perovskite structure at room temperature,leading to the torsion of Pb-I bonding.Hence,this work aims to stabilize the perovskite structure of CsPbI3 by component engineering,quantum confinement effect and ammonium iodide asisted crystallization,further enhancing the performance and stability of solar cells by surface passion.The tolerance factor could be increased by replacing the I ions by Br ions,resulting in the better phase stability of CsPbI3.However,it's hard to solve the bromide in DMF.Herein,a general strategy of solution engineering has been implemented to enable a wide solutionprocessing window for high open-circuit-voltage(VOC)(?1.3 V)and power conversion efficiency(PCE)(?12.5%).We introduce a nontoxic solvent of dimethyl sulfoxide(DMSO)and an assisted heating process in the fabrication of CsPbI3Br to control the improved crystallization.A wide solution-processing window including a wide range of solvent components and solute concentrations has been realized.The CsPbI3Br perovskite solar cells exhibit a high PCE up to 12.52%.More importantly,these devices demonstrate a remarkable VOC of 1.315 V.The unveiling wide solution-processing windows with enhanced solution processability facilitating potential industrial application especially for tandem solar cells.During the fabrication of CsPbI2Br films.rich lead vacancy could cause deep trap states on the surface of the perovskite film,leading to much charge recombination.Herein,Pb2+ solution post-processing strategy is introduced to passivate the deep trap states of CsPbI3Br films.The dissociative Pb2+ in the solution effectively combines with the excess halide ions on the perovskite surface to reduce the deep trap states of Pb vacancy(VPb)and I interstitial(Ii).As a result,the average photoluminescence lifetimes rave of the perovskite film prolonged nearly double after passivation.The trap density of perovskite is effectively decreased from 8×1016 to 6.64×1016 cm-3.The CsPb2Br solar cell shows the VOC as high as 1.29 V and PCE of 12.34%with small hysteresis.The postprocessing method would provide an avenue to improve further the efficiency of inorganic perovskite solar cells via reducing surface traps.The inorganic perovskite CsPbI3 which exists in the form of a quantum dot(QD)shows a stable perovskite phase.We exploit a fully automated spray-coated technology with ultrathin-film purification(UFP)for commercial large-scale solution-based process of colloidal inorganic perovskite CsPbI3 QD films towards solar cells.This process is in the air outside the glove box.To further improve the performance of QD solar cells,the short-chain ligand of phenyltrimethylammonium bromide(PTABr)with benzene group has been introduced to partially substituted for the original long-chain ligands of the colloidal QD surface.This process not only enhances the carrier charge mobility within the QD-film due to shortening length between adjacent QDs,but also passivates the halide vacancy defects of QD by Br-from PTABr.The colloidal QD-solar cells show PCE of 11.2%with an VOC of 1.11 V,short current density(Isc)of 14.4 mA/cm2 and fill factor(FF)of 0.70.Due to the hydrophobic surface chemistry of PTABr-CsPbI3 film,the solar cell can maintain 80%of initial PCE in air ambient for one month without any encapsulation.Such a low-cost and efficient spray-coating technology also offers an avenue to the film fabrication of colloidal nanocrystals for the electronic devices.However,too many grain boundaries in the perovskite QD layer block the transport of carriers,resulting in the potential loss of solar cells.Hereon,we devise a gradient band alignment(GBA)homojunction layer of CsPbI3 PQD to facilitate the charge extraction and reduce the potential loss of the solar cells.The GBA structure facilitated the charge extraction and increased the carrier diffusion length of the PQD layer because of the additional driving force for electrons.In addition,the homojunction made by the same substance could minimize the lattice mismatch of the active layer.As a result,the champion solar cell based on the GBA homojunction layer achieved a high open voltage VOC of 1.25 V and PCE of 13.2%.Although the peovskite structure of CsPbI3 can be stabilized by Br dopping and synthesis of quantum dot,the bandgap is inevitably enlarged,resulting in the reducing of absorption range.Furthemore,Br dopping could increase the degree of phase separation.Too many organic ligands and grain boundries are harmful to the efficiencies of devices.We introduced the dimethylamine hydroiodate(DMAI)in to the precursor of CsPbI3 soluton to obtain the pure CsPbI3 polycrystal film.DM AI combine with CsPbI3 in the solution,improving the crystallization.We speculate that DMAI exists in the grain boundries,and is evaporated during the annealing process.Finaly,based on CsPbI3 film of ? phase,the PCE of 19.1%is obtained which is at an advanced level in photovoltaic field.