Bulk,Interface,and Surface Optimization Enhanced CsPbI₃ All-Inorganic Perovskite Solar Cells

Since the 21st century,perovskite solar cells have rapidly increased their photoelectric conversion efficiency from 3.8%to 25.7%due to their excellent photoelectric properties,such as tunable bandgap,long carrier diffusion length,low non-radiative recombination and high absorption coefficient.So far,organic-inorganic hybrid perovskite solar cells still have the problem of instability,especially the thermal degradation affected by high temperature and the phase structure is easy to phase change.In recent years,Cs Pb I₃ perovskite has attracted more and more attention due to its remarkable thermal stability and excellent light absorption ability（bandgap width of about 1.69 e V）.This inorganic perovskite material is not only an ideal light-absorbing layer candidate for single-junction solar cells,but also can be used as a top cell for tandem solar cells.These advantages make Cs Pb I₃-based perovskite solar cells（PSCs）widely concerned in practical applications.However,the low tolerance factor and fast crystallization speed of Cs Pb I₃ material lead to poor crystallization quality of perovskite film formation,high density of defect states,and poor stability of phase structure,which become an obstacle to prepare efficient and stable inorganic perovskite solar cells.In this paper,the quality of the film and the stability of the perovskite structure phase were improved by optimizing the interface between the bulk phase and the surface of Cs Pb I₃perovskite,so as to improve the photoelectric conversion efficiency and stability of inorganic perovskite solar cells.The content and results of this research work are as follows:（1）The Cs Pb I₃ perovskite thin film was improved by using succinonitrile（SN）containing cyanide as an additive,and the defect density in the perovskite thin film was effectively reduced,and an efficient and stable perovskite solar cell was obtained.It is found that the cyanide group in the additive SN can coordinate with the[Pb I₆]^4-octahedron in the perovskite nucleation process to improve the crystalline quality of Cs Pb I₃ films.In addition,the cyanide group will coordinate with the Pb2+defect of the perovskite to reduce the defects in the perovskite body,thereby inhibiting the non-radiative recombination.The results show that the efficiency of Cs Pb I₃-based PSCs increases from 14.53%to 16.17%after the addition of SN.At the same time,the improved perovskite layer with lower defect state density effectively prevents water vapor erosion,thereby improving the stability of the device.The initial efficiency of 86%is still maintained after 500 h storage in 25%humidity environment,which is 32.03%higher than the control.（2）Inorganic perovskites are easily eroded by water vapor in air and undergo phase transformation,resulting in poor device performance.In this chapter,a hydrophobic sulfide layer is formed by passivating the perovskite interface to prevent the erosion of external water vapor and improve the performance of battery devices.Firstly,lead acetate（Pb（Ac）₂）was added to the perovskite layer to improve the quality of the perovskite film and construct a layer of surface lead-rich perovskite.Subsequently,sulfur-rich double（trimethylsilyl）thioether（TMS）was coated at the upper interface of the perovskite to form a sulfide layer,and the hydrophobic Pb-S bond prevented external water vapor from invasion of the perovskite layer.The Pb-S bond interaction at the interface induces the dipole moment and increases the valence band of the perovskite,which leads to the increase of the open-circuit voltage of the perovskite cell device.Moreover,the functionalization of Pb-S bonds on the perovskite surface promotes hole extraction while inhibiting interfacial non-radiative recombination.The TMS passivated lead-rich perovskite device achieves a photoelectric conversion efficiency of 16.84%,and maintains an initial efficiency of 90.09%after storage in a 25%humidity environment,which is 89.09%higher than the control.（3）The additives in the traditional hole transport layer Spir-ome TAD can induce the inorganic perovskite to accelerate the phase transition,resulting in poor stability of the battery.P3HT with high hydrophobicity was used as the hole transport layer instead of Spiro-OMe TAD,and 1-ethyl-3-methylimidazole tetraborate（EMIMBF₄）was added to P3HT to induce P3HT to grow in orientation,improve the carrier mobility of P3HT,and increase the hydrophobicity.The performance of the perovskite solar cell device based on the improved P3HT is improved from 10.17%to 12.37%,and the original efficiency is still 77.02%when stored in the environment of 45%humidity for 500 h,which is 81.43%higher than the control.