Study On Phase Stabilization And Photovoltaic Performance Of All-inorganic Halide Perovskite

Compared to organic-inorganic hybrid perovskites（OIHP）,inorganic CsPbX₃perovskite materials exhibit better thermal stabilities,thus showing promising prospects in the field of perovskite solar cells（PSCs）.Within the inorganic compositions,CsPbI₃perovskite possesses a smaller bandgap（E_g）about 1.7 e V,which is favorable for high-performance single-junction PSCs or top cell in silicon/perovskite two-terminal tandem solar cells（TSCs）.However,CsPbI₃ perovskite phase is unstable due to small ionic radius of the Cs⁺cation,leading to a non-photoactive phase at room temperature.The hydrogen iodide（HI）additive commonly is adopted to fabricate black CsPbI₃ perovskite-phases film.However,the underlying mechanism and issues in the preparation of films or devices still need to be further investigated to obtain stable and high-performance CsPbI₃PSCs at room temperature.In this doctoral dissertation,Firstly,the myth of material composition with HI additive in CsPbI₃ perovskite precursor solution was revealed in detail,and the effect of precursor materials in producing high-quality CsPbI₃ perovskite films or devices systematically were studied.Subsequently,a reasonable strategy via condensation reaction at film surface was then designed to improve the crystallization quality of the films and charge carriers transfer rates,eventually achieving high-performance single-junction formal（n-i-p）structured CsPbI₃ PSCs.Finally,the CsPbI₃perovskite was used in a top cell of crystalline silicon/CsPbI₃ perovskite two-terminal TSCs devices.By optimizing the non-radiative recombination in the interface of PSCs,an excellent photovoltaic performance single-junction inverted（p-i-n）structured solar cells and crystalline silicon/CsPbI₃ perovskite two-terminal TSCs were obtained.The detailed research contents and results are as followed.HI additive was used to prepare photoactive CsPbI₃ perovskite films at room temperature,but the presence of organic components was confirmed in inorganic CsPbI₃perovskite films in this research.In order to confirm the organic components,the precursor powder was synthesized by reacting lead diiodide（PbI₂）and HI in N,N-Dimethylformamide（DMF）solvent.The organic component was dimethylammonium ion CH₃NH₂CH₃⁺（DMA⁺）via characterization analysis of crystal structure,surface morphology,and elemental compositions with molecular structure analysis,which further form DMAPbI₃ with PbI₂.The influence of DMAPbI₃ precursor on the preparation of CsPbI₃ perovskite films and device performance was systematically studied.Different compositions of perovskite films were prepared by varying the molar ratio of Cs I/DMAPbI₃ in precursor solution,and it was found that DMAPbI₃ could effectively manipulate the film crystallization process,significantly improve the film quality,phase stability,and device performance.The optimized CsPbI₃ PSCs achieved a power conversion efficiency（PCE）of 14.3%.This method provides a new insight and strategy for the preparation of CsPbI₃ PSCs via the HI additive.Further investigation found that DMA⁺could effectively manipulate the film crystallization process and improve film quality,but residual DMA⁺in the film led to the presence of heterogeneous components and increased the defect density,hindering further improvement of device performance.However,removal of DMA⁺usually requires temperatures above 300^°C,which impeding the development of CsPbI₃ perovskite in device applications on temperature sensitive substrates.In this research,a method using an intermolecular condensation reaction was designed for removing residual DMA⁺in the film at lower temperatures to modify the surface of CsPbI₃ perovskite films.It was found that 2-thiopheneboric acid（2-TBA）molecules undergo condensation reaction to produce H₂O molecules that could effectively lower the volatilization temperature of DMA⁺and remove the residual organic DMA⁺from the surface.In the meantime,the remaining thiophene functional groups could inhibit the formation of surface defects,significantly improving the surface morphology of CsPbI₃ films.By optimizing the energy-level structure of the device,hole extraction efficiency was enhanced.As a result of the optimized physical properties,CsPbI₃ PSCs based on conventional n-i-p structure achieved a PCE of 19.18%,thereby standing for a significantly improved device performance.CsPbI₃ perovskite exhibits an ideal optical bandgap for absorber layer of top cell in silicon/perovskite two-terminal TSCs,demonstarating promising prospects for applications.Compared to the n-i-p structure,the single-junction p-i-n structured CsPbI₃cells possess better stability and is more suitable for TSCs.In this section,a series of characteristic functional group molecules were adopted to reduce the severe non-radiative recombination at the interface between the CsPbI₃ film and the electron transport layer（ETL）in such p-i-n structured PSCs.Research results indicate that surface treatment effectively reduced the photocarrier loss and therefore significantly improved the open-circuit voltage(V_OC)of p-i-n structured CsPbI₃ PSCs,yielding a top PCE of 19.0%for the single-junction champion.In addition,a PCE exceeding 20%and a high V_OC of 1.73V were achieved by applying the optimized silicon/CsPbI₃ perovskite two-terminal TSCs.This doctoral dissertation systematacially study the relevant issues or challenges concering CsPbI₃ perovskite for the phase-stability,high-quality thin film preparation,device interface optimization,the fabracation of high-performance single-junction PSCs and TSCs.These research results give insights into the CsPbI₃ perovskite,paving the way for further development and commercial application of CsPbI₃ PSCs.