Research On The Manipulation Of The Microstructure At Bulk And Interface Of Perovskite Films To Improve The Efficiency And Stability Of Solar Cells

As an emerging photovoltaic technology,perovskite solar cells（PSCs）exhibit high photoelectric conversion efficiency（PCE）and versatile preparation methods,thus exhibiting promising prospects.Currently,the record PCE of PSCs has exceeded 26.1%achieved in laboratory conditions.However,the commercial viability of this technology faces challenges in terms of balancing between high efficiencies and long-term stabilities,thereby hindering the potential of PSCs.This dissertation follows the international trend of development.Based on the extensive availability of perovskite materials,controllable film growth technology,and flexible adjustable structural dimensions.A series of PSCs research were carried out focusing on Perovskite film growth mechanisms,grain boundaries,and surface microstructure regulation.The influence of solvents,lead sources on the orientation of crystal and microstructure morphology of perovskite films was investigated.The micro-mechanism of non-halide anions delaying the crystal growth rate of perovskite during the growth process was revealed.The microstructure such as Pb I₂-embedded perovskite film grain boundaries and surface low-dimensional perovskite were constructed,achieving controllable adjustment of the perovskite film bulk phase and surface microstructure,thereby promoting the efficiency and stability enhancement of PSCs.This work provides valuable insights for the development of efficient,stable,and low-cost PSC technology.The detailed research content and results of this dissertation are as follows:1.In response to the unclear impact of crystal orientation of perovskite on the optoelectronic properties and device performance,the research utilized lead acetate to prepare perovskite precursor solution,altering the free energy of the precursor solution by adding varying concentrations of dimethyl sulfoxide（DMSO）to achieve precise control of the orientation of perovskite crystal from（110）to（200）.Research results demonstrate that the（200）orientation of perovskite films exhibits smaller microstrain,lower defect density,and longer carrier lifetime.Ultimately,the application of perovskite films with（200）orientation in PSC devices yields an efficiency of 20.8%,marking the highest PCE at that time for preparing PSCs using non-halide lead.2.In response to the unclear relationship between the interior grain boundaries passivation of perovskite films and device performance,the research substituted lead formate,similar in size to halide ions,to achieve a microstructure where lead iodide is vertically embedded in the grain boundaries of perovskite thin films.By adjusting parameters such as the concentration of DMSO in the precursor solution and the chemical stoichiometry of lead formate to MAI,precise control over the lead iodide content embedded at the grain boundaries of the perovskite films was achieved.Research results indicate that an appropriate amount of Pb I₂ embedded at the perovskite grain boundaries can effectively hinder the transfer of charge carriers across the grain boundaries,thus passivating defects in the perovskite films and enhancing the carrier lifetime to as long as1713.9 ns.Benefiting from the long carrier lifetime comparable to the single crystals,corresponding PSCs achieved a PCE of 19.4%.3.To achieve the preparation of high-quality perovskite films,this dissertation further investigates the impact of non-halide anions on the crystallization kinetics of perovskite films based on the theory of crystal dynamics regulation.The research findings indicate that the non-halide anion HCOO^-increases the activation energy of the perovskite growth reaction,effectively decelerating the crystallization rate of the perovskite film,enhancing the uniformity of the perovskite film,enlarging the grain size,improving the crystal orientation,reducing the defect density of the film,and thus achieving optimization of the film’s microstructure.The abovementioned modification results are conducive to an enhanced open-circuit voltage and fill factor of PSCs,achieving a device PCE of 22.5%.Moreover,after 1000 hours of aging in environmental humidity,device efficiency still maintains 98%of its initial performance,demonstrating excellent moisture stability.4.To further enhance the stability of PSCs,this dissertation explores an interface engineering.By constructing a surface microstructure on the top surface of the perovskite film that combines both chemical passivation and efficient carrier transport properties.Different from the conventional full coverage with 2D perovskite,this networked morphology with can balance between surface passivation efficacy and carrier transport across low-dimensional perovskite by controlling the pore size therein.Consequently,PSCs with a high PCE up to 24.6%are prepared.Importantly,in terms of device stability,low-dimensional network perovskite can effectively block moisture from eroding the underlying perovskite while inhibiting the cation volatilization due to high-temperature decomposition of the underlying perovskite,thereby improving the humidity and thermal stabilities of PSCs.After more than 1000 hours of aging in humidity and illumination,the devices can still maintain 94.0%and 85.7%of the initial PCE.This dissertation achieves the enhancement of perovskite film crystal quality,optoelectronic characteristics,and stability by regulating both the bulk phase and interfacial microstructures of the perovskite film,thereby fabricating highly efficient and stable PSCs.It also proposes enhancing PCE and stability of PSCs by utilizing surface low-dimensional network perovskite,offering new research strategies and ideas for the future commercial application of low-cost,high-efficiency,and highly stable PSCs technology.