Back Contact Regulation Of Carbon-based Sb₂（S,Se）₃ Thin Film Solar Cells

Antimony sulfide（Sb₂（S,Se）₃）has attracted extensive attention as a potential absorber material for thin film solar cells,due to its excellent light absorption coefficient,adjustable band gap in the range of 1.1-1.7 e V,abundant element reserves and non-toxicity.Thanks to unremitting efforts,the conversion efficiency of Sb₂（S,Se）₃solar cells using organic hole transport layer materials（HTL,i.e.Spiro-OMe TAD）and Au metal electrode thin film has exceeded 10.7%.However,the development of the related devices is stilled limited by the unstable HTL and expensive gold electrode,which greatly increases the cost of devices and further restricts the road to commercial development.Therefore,it is urgent to develop an inorganic back contact material to replace it.Carbon is a low-cost and stable electrode material,which is considered as a potential electrode candidate for Sb₂（S,Se）₃solar cells.However,due to the poor contact between Sb₂（S,Se）₃and carbon electrode interface and the absence of electron barrier,serious carrier recombination exists in the back interface of carbon-based Sb₂（S,Se）₃solar cells,which deteriorates the device performance.In this thesis,,on the one hand,PbS was inserted between Sb₂（S,Se）₃/Carbon,on the other hand,environmentally friendly MoS₂electron barrier layer was explored to explore the mechanism of action,band arrangement and device performance of Sb₂（S,Se）₃and Carbon interface.In addition,due to the suitable band gap and high light absorption coefficient of MoS₂polycrystalline thin film,its application in the absorption layer of thin film solar cells is also studied in this thesis.The specific research contents are listed as follows:（1）PbS regulates the back contact of carbon-based Sb₂（S,Se）₃solar cell.The ultra-thin PbS layers prepared with different strategies were used to modify the back contact-interface of the device.Compared with the generic PbS nanoparticles-based routes,the hydrothermal-derived PbS layer is more uniformly and closely coated on the rear surface of Sb₂（S,Se）₃by enjoying a unique in-situ anchoring process.As a result,a benign back contact with a well-matched interface effectively reduces the contact resistance and promotes the hole collection efficiency.Consequentially,the fill factor（FF）of the device boosts from 33.0%（control device）to 65.1%（with hydrothermal-based PbS）and also delivers a device efficiency enhancement from 3.1%to 8.0%,which is the highest FF and the power conversion efficiency（PCE）for the carbon-based Sb₂（S,Se）₃solar cells so far.This work paves a potential route for high-performance carbon-based Sb₂（S,Se）₃solar cells.（2）Green MoS₂film improves the interface characteristics of wide bandgap Sb₂（S,Se）₃/Carbon.MoS₂nanocrystalline thin films are prepared by thermal evaporation method and applied as back contact material for Sb₂（S,Se）₃solar cells.MoS₂has a matched energy level structure with Sb₂（S,Se）₃,and the corresponding devices show better rectification behavior and generate larger internal potential to provide higher driving force to separate carriers.Finally,the efficiency of carbon-based Sb₂（S,Se）₃device is improved from 4.0%to 6.1%by optimizing the thickness of MoS₂film.It is found that the introduction of MoS₂film can significantly reduce the series resistance,and prevent the movement of electrons to the back electrode,and reduce the back interface recombination of the device.（3）MoS₂polycrystalline film is applied in the absorption layer of solar cell.Due to its high absorption coefficient and carrier mobility,MoS₂is expected to be a potential absorption material for planar heterojunction solar cells.In this study,we used in-situ hydrothermal growth and post-annealing method to deposit MoS₂polycrystalline thin films on ITO/Ti O₂/Cd S substrates.The buffer layer of Cd S is a hexagonal crystal structure,which provides a stable template for the quasi-epitaxial growth of MoS₂through the shared sulfur atoms,thus forming a benign interface of Cd S/MoS₂.The effects of growth characteristics,morphology and optical properties of MoS₂on device performance were systematically studied.Finally,p-type MoS₂poly-crystal absorbent with a thickness of 305 nm was used to obtain a preliminary efficiency of 0.12%,and the device showed excellent stability.Further use of the one-dimensional Solar Cell Capacitance Simulation program（SCAPS）reveals the factors that affect device performance efficiency.This work provides an in-situ growth pathway for the construction of Cd S/MoS₂planar heterojunction,and the MoS₂polycrystalline film is expected to be a candidate material for the absorption layer of low-cost solar cells.