Inorganic Semiconducting Nanocrystalline Materials And Their Application In Thinfilm Solar Cells

The aim of making inexpensive and highly efficient solar cells has attracted great attention from researchers.The R&D centers around the globe are exploring and developing new active materials to fit the demand of photovoltaics,based on low cost processes.Huge efforts have been dedicated to the thinfilm photovoltaics,by developing semiconducting materials and devices for the high efficient and low cost aims.In which,the organic and perovskite thin film solar cells have developed very fast.Efficiency over 14%has been achieved for single organic solar cells.And efficiency over 22%has been obtained for organic-inorganic perovskite solar cells.However,these techniques still suffer from problems,like controlling of the crystallization and morphology of active layer,low device efficiency,instability and environment toxicity.Thus exploring and developing low cost,high efficient,stable and environmentally friendly thinfilm photovoltaics is of great significance.In the past decade,semiconducting quantum dots?QDs?or nanocrystals?NCs?materials and their photovoltaic applications have been hot research topics,because the advantages of this class of materials,size-dependent electronic energy bandgap control due to quantum confinement effect,ideal film depositing and morphology controlling properties due to the self-assembly of QDs,better chemical stability and less environment toxicity.This thesis is focused on developing of different inorganic semiconducting nanomaterials and their application in thinfilm photovoltaics.The main content can be summarized as follows:In the first part of the thesis,we investigated inorganic cesium lead halide semiconducting quantum dots and their application in thinfilm photovoltaics.Highly crystalline materials were synthesized by two different approaches,including a high temperature route and a low temperature method.Inorganic-polymer hybrid solar cells based on solution-deposited layers of CsPbX₃ nanocrystals were successfully fabricated in ambient,with and without post treatments.The solar cells employing CsPbBr₃ nanocrystals with short ligands,obtained from low temperature route,outperformed the devices with long ligands.The devices exhibited an efficiency up to 1.16%,with an open circuit voltage(V_oc)of 0.87 V,a fill factor of 56.2%and a short-circuit current density(J_sc)of 2.38 mA/cm².Our results indicated that,based on pure inorganic perovskite quantum dots active layer,solar cells working properly in ambient conditions can be obtained.And by employing short ligands in low temperature synthesis route,the post treatment of ligands in QDs layer can be avoid,and the film conductivity and device performance can be improved.In addition,we reported the synthesis and application of non Pb-based and low environment toxic AgBiS₂ QDs in thinfilm solar cells.Stable QDs solution and good quality thinfilms can be deposited with MeOAc purification combined with suitable ligand treatments.When used as photoactive layers in thinfilm hybrid solar cells,the well optimized QDs presented PCE³%with structure of ITO/ZnO/AgBiS₂/polymer/MoO₃/Ag.Decent performances obtained from our polymer-AgBiS₂ solar cells demonstrate a good prospects of environmental friendly materials based solar cells.Moreover,when used as cathode interlayer,AgBiS₂ QDs solar cells provided maximumefficienciesof5.56%basedontheinvertedstructure ITO/AZO/AgBiS₂/PCE10:PC₇₁BM/MoO₃/Al.Zincoxide?ZnO?is one of the most frequently utilized n-type layer,having several advantages including easy of synthesis,desirable bandgap and suitable optoelectronic characteristics.However,the unwanted traps may lead to high recombination thus resulting in poor final device performance.Improved performance can be realized by modifying the cathode interlayer.A gallium doped zincoxide?Ga:ZnO?interlayer material with propylamine as the stabilizer was developed at room temperature.The GZO nanocrystals,with 100°C thermal-annealing based CIL,when used with organic active layer?PBDBT:IT-M?in the inverted solar cell acquired a best PCE of 10%.The presented results are comparable to the reported literature and indicate that the modified ZnO interlayer could improve the electron transporting and collecting efficiency by reducing the recombination inside the device leading to better performance.