Enhancing Repeatability And Stability Of Lead Halide Perovskite Solar Cells

Organic-inorganic hybrid lead halide perovskite materials have set off a research upsurge in the fields of solar cells,photodetectors and light-emitting devices because of their excellent optoelectronic properties（such as high absorption coefficient,long carrier diffusion length,low exciton binding energy,low temperature solution processibility,etc.）.Solar cells made of perovskite materials have attracted great attention because of their increasing power conversion efficiency（PCE）,although they have only experienced more than a decade of development.So far,the certified power conversion efficiency of perovskite solar cells has reached 25.7%,which is comparable to that of traditional silicon-based solar cells.However,the stability issue of perovskite solar cells is still a big concern for the commercialization.In addition to the widespread concern about stability,improving fabrication repeatability is also a key issue that needs to be addressed for lead-halide perovskite solar cells moving toward industrialization.Since charge transport layer materials and lead halide perovskite absorbers are susceptible to external stresses such as light,heat,moisture and oxygen during the preparation process,these factors often lead to poor repeatability of the materials during the preparation process.In this dissertation,from the perspective of improving the fabrication repeatability and stability of perovskite solar cells,the influence of the photo-electric parameters of the transparent conducting substrate on the performance of perovskite solar cells was first investigated.The effect of hydrogen peroxide（H₂O₂）on enhancing the reproducibility of tin dioxide（Sn O₂）electron transport layer preparation was then investigated.Then a strategy to stabilize the lead halide perovskite grain boundaries and enhance their PCE and stability was demonstrated.Finally,a method for preparing high quality perovskite films with high repeatability through a physical barrier method to retard the volatilization of organic ammonium salts was developed.The main contents of this study are summarized as follows:（1）The influence of the photo-electric parameters of transparent conductive substrates on lead-halide perovskite solar cells had been systematically studied,laying a solid foundation for the preparation of highly efficient and stable lead-halide perovskite solar cells.（2）By modifying the tin dioxide precursor with hydrogen peroxide,the repeatability of the tin dioxide electron transport layer and long-term stability of device was effectively improved.Due to its strong oxidizing property,hydrogen peroxide was able to oxidize divalent tin ions in the tin dioxide precursor to tetravalent tin ions,which improved the electron extraction and transport capability of tin dioxide.Equally important,the introduction of hydrogen peroxide reduced the oxygen vacancy defect density on the surface of tin dioxide films.Therefore,the strategy enhanced the performance and long-term stability of lead-halide perovskite solar cells,and the device with H₂O₂–Sn O₂ kept about 94%of initial PCE after 1000 h stored in ambient atmosphere（humidity～20 RH%）in the dark,while those with Sn O₂ maintained only86%under the same condition.（3）The stability of grain boundaries of lead halide perovskite films was enhanced by pretreating the unannealed lead halide perovskite films with a small amount of oleylamine chloride（OACl）solution.The OACl was able to anchor at the grain boundaries of lead halide perovskite,effectively protecting the grain boundaries from thermal decomposition.In addition,the pre-annealing treatment strategy successfully induced the precipitation of lead iodide on the grain surface instead of on the grain boundaries of the lead halide perovskite films,effectively passivating the surface defects and suppressing the charge recombination between the perovskite and the hole transport layer.As a result,power conversion efficiencies of up to 24.95%and an ultra-high 85.5%fill factor were obtained.The unencapsulated cells maintained 81%of their initial efficiencies after 1000 h of continuous operation at maximum power point at about 55℃in an inert atmosphere,showing improved photostability.（4）The volatilization of organic ammonium salts during the annealing of lead halide perovskite films was suppressed by a physical barrier method,which greatly enhanced the crystal quality of lead halide perovskite materials.Due to the partial decomposition of lead halide perovskite films during outdoor annealing process,excess lead iodide remained at the grain boundaries,which seriously affected the quality of perovskite films.Physical barrier method could prepare lead halide perovskite thin films with high quality.Compared with the conventional preparation method,the size of lead halide perovskite crystals obtained by physical barrier method was more than ten times larger and the carrier life was longer,showing a good application prospect.