Study On Impact Of Morphology And Device Structure On Silver Bismuth Iodide Solar Cells

Over the last few years,lead-halide perovskites have captured a great deal of attention,due to their outstanding performance as active materials for photovoltaics.While extremely promising,lead-halide perovskites bring along severe concerns regarding their toxicity and environmental hazard.This has prompted the search for lead-free perovskites.In particular,a promising route involves bismuth-based perovskites.AgBixI3x+1 is a kind of bismuth-based perovskite that has attracted significant attention.According to the different chemical formulation of silver iodide(AgI)and bismuth triiodide(BiI3),this family of materials can be roughly divided into Agl-rich compounds(Ag3BiI6,Ag2BiI5)and BiI3-rich compounds(AgBiI4,Ag2BiI7).The AgI-rich compounds are particularly promising for photovoltaics in view of literature indications,and they offer space for further improvement in terms of film morphology,solar cell device structure,device efficiency.In this thesis,we report the impact of a number of processing and device architecture strategies on photovoltaic performance.In particular,we study film morphology in relation to different coating methods(both one-step spin coating and anti-solvent spin coating),to the addition of a strong acid in the precursor solution,and to different annealing protocols.Furthermore,we study the influence of different device structures on the device efficiency.This thesis consists of the following parts:1.A brief introduction of the main concepts,classification,working principles and device structures of solar cells,and summary of the development of perovskite solar cells,with a focus on lead-free perovskites(Chapter 1).2.A detailed description of the materials,characterization equipment and general methods used in our experiments(Chapter 2).3.Development of a method to improve the solubility of the precursors by adding trace hydrogen iodide in the starting solution,which is then used for the deposition of Ag2BiI5 films with optimized morphology through a one-step spin coating method(Chapter 3).4.The optimization of an annealing method based on anti-solvent spin coating method,which is utilized for the conditioning of AgI-rich compounds(Ag3BiI6,Ag2BiI5)films towards large grain size and reduced pinhole count(Chapter 4)5.Introduction of the influence of a hot-coating method on the impurity phase and the grain size in AgI-rich compounds(Ag3BiI6,Ag2BiI5)films,and a preliminary experimental investigation of the nature of the impurity phase(Chapter 5).6.Fabrication and device performance evaluation of Ag2BiI5 devices realized through different film deposition methods discussed earlier,and analysis of the impact of the fabrication methods and testing methods on device performance and hysteresis,respectively(Chapter 6).7.The possibility of Ag2BiI5 as photodetector is evaluated(Chapter 7).8.Summary and outlook of the entire work(Chapter 8).