Study On High-Performance Perovskite Photovoltaic Devices Based On Bulk/Interface Regulation

Recently,perovskite photovoltaic materials have triggered a research boom in the field of photovoltaic cells due to their excellent optoelectronic properties.Benefiting from sustained attention and a large amount of R&D investment,the research on perovskite photovoltaic devices has continuously made new progress.The certified efficiency of perovskite photovoltaic cells prepared in the laboratory has reached25.7%,surpassing many new thin-film solar cells and comparable to monocrystalline silicon cells.Nevertheless,to truly realize the commercialization of perovskite photovoltaic devices,some issues are inevitable,including stability,efficiency bottlenecks and large-scale preparation.Since the perovskite absorber layer is the kernel of perovskite photovoltaic devices,improving the crystal quality of the perovskite absorber layer is the key to solving these problems.One effective way to improve the crystal quality of the absorber layer is to regulate the bulk crystallization process of perovskite films.Through reasonable bulk crystallization regulation,the defects in perovskite films can be effectively reduced,meanwhile,the defect-induced phase transition can be significantly suppressed.Macroscopically,the crystallization process of perovskite is directly related to the uniformity of perovskite film,which further affects the large-scale preparation of perovskite photovoltaic devices.Another way to improve the crystal quality of perovskite absorber layer is to modify the interface of perovskite films,including passivating the defects on the surface and interface of the perovskite films,regulating the interfacial energy levels,and using physical or chemical isolation at the interface.These interfacial strategies can significantly suppress the nonradiative recombination of carriers and the phase transition of the perovskite films.Therefore,the works of this thesis focus on the bulk and interface regulation of the perovskite absorber layer.With strategies such as additives,interface modification and improved film deposition process,high-quality perovskite films and high-performance perovskite photovoltaic devices have been prepared.The specific research works are as follows:（1）High-quality inorganic CsPbI₃ films were prepared by regulating the perovskite intermediate phase with inorganic ammonium halide additives.The atomic interaction between the ammonium ion and the Pb-I framework can effectively decompose the large-sized colloidal particles composed of the Pb-I framework in the precursor solution,thereby retarding the nucleation of the perovskite intermediate phase.The prepared CsPbI₃ film has larger grain size and better contact at the grain boundaries and interfaces.Benefiting from the reduced grain boundaries,defect state density,and charge-trapping activity,the nonradiative recombination of carriers in the CsPbI₃ film is effectively suppressed and the charge transport ability is significantly enhanced.These advantages are helpful to improve the performance of inorganic CsPbI₃perovskite solar cells.Finally,the prepared cells achieved a high power conversion efficiency（PCE）of 18.71%and a fill factor of 0.83-0.84.Meanwhile,the device exhibited excellent photoelectric stability under continuous illumination and high bias voltage.After 2000 hours of continuous operation,the device can still maintain 96%of its initial PCE.The strategy of regulating the perovskite intermediate phase in this work provides ideas for the fabrication of high-performance CsPbI₃ solar cells.（2）A method for passivating and stabilizing black-phase CsPbI₃ with thermally stable low-dimensional perovskites has been developed to achieve high-quality CsPbI₃films and high-performance photovoltaic cells.Generally,it is very difficult to achieve low-dimensional structures passivation on CsPbI₃ films by post-processing strategies.However,the preparation process of high-quality CsPbI₃ films involves high-temperature annealing,which is a challenge to the thermal stability of low-dimensional perovskites.Therefore,we investigated the thermal stability of several selected organic ammonium iodide salts and their possibly related low-dimensional perovskites firstly,and then added the selected organic ammonium iodide salts to the perovskite precursor solution.We demonstrated that PTAI-based low-dimensional perovskites were formed in situ at the grain boundaries and surfaces of CsPbI₃,which can significantly improve the morphology of CsPbI₃ films and reduce the density of defect in the films,thereby suppressing nonradiative recombination of carriers at the surface and interface of CsPbI₃ films.Finally,the best cell we fabricated achieved a record efficiency of 21%and enhanced stability.This work provides a rational low-dimensional perovskites passivation strategy for efficient and stable CsPbI₃ photovoltaic cells.（3）An interfacial gradient heterostructure was constructed as an effective defect passivation and energy level modification strategy to realize high-performance CsPbI₃photovoltaic devices.The CsPbI₃ film was post-treated with quaternary ammonium bromide to achieve a gradient distribution of bromide ions and surface termination of organic cations at the interface,thereby realizing the construction of an interfacial gradient heterostructure.We demonstrated that the interfacial gradient heterostructure at the interface can passivate defects,suppress the formation of lead clusters,as well as optimize the interfacial energy level alignment in the device,thus reducing nonradiative recombination.Finally,we obtained a high efficiency of 21.31%for small-area CsPbI₃solar cells and a record efficiency of 16.6%for CsPbI₃ photovoltaic minimodules（aperture area:12 cm²）prepared by blade coating.In addition,the stabilities of CsPbI₃films and devices based on the interfacial gradient heterostructure were significantly enhanced.This work provides an effective interface modification strategy for the fabrication of high-performance CsPbI₃ photovoltaic devices.（4）A meniscus-modulated blade coating was developed for the fabrication of high-performanceα-FAPb I₃ photovoltaic devices.In this work,two solvents with significantly different volatilities were first compared.For blade coating,although solvents with low boiling point and high saturated vapor pressure are conducive to achieve uniform perovskite films,the excessively fast nucleation and crystallization processes are detrimental to the deposition of high-quality perovskite films.Therefore,a solvent with high boiling points and low saturated vapor pressures was selected in this work.We demonstrated that,high-throughput meniscus coating follows the Landau-Levich deposition regime when using solvents with high boiling point and low saturated vapor pressure.Under this regime,it is difficult to reduce the thickness of the perovskite film to a suitable range.However,modulating the meniscus by high-speed nitrogen flow can effectively reduce the amount of solution dragged out from meniscus by viscous force and Marangoni flow,thereby precisely controlling the thickness of the perovskite film.This work further verifies that the meniscus-modulated blade coating method is suitable for high-concentration precursor solutions,thus the preparedα-FAPb I₃ film has larger grain size,excellent crystal orientation and good uniformity.Finally,we achieved an efficiency of 24.57%on a small-area cell and an aperture-area efficiency of 22.66%on a perovskite photovoltaic module.In addition,the prepared cells and modules exhibited excellent stability.This work provides a more applicable blade coating method for the development of high-performance perovskite photovoltaic devices.