Performance Study Of Carbon-based Perovskite Solar Cells Based On Perovskite Thin Films And Interface Optimization

With the development of human and technology,the global demand for energy is increasing.Fossil energy is the main energy for human development,its non-renewable and use lead to environmental pollution.Therefore,people urgently need to develop renewable energy to achieve economic development and protection of ecological environment.Solar energy has the characteristics of clean,renewable and huge reserves,and its effective development and utilization has always been paid attention to by the world.Solar cells have been widely utilized because they can conversion directly and efficiently solar energy into electrictiy.At present,commercial solar cells are mainly based on crystalline silicon solar cells.However,crystalline silicon solar cells have the limited applications in wearable devices,smart devices and other fields due to the brittleness of crystalline silicon materials,the complexity of the preparation process,and the heavy weight of components.Perovskite solar cells（PSCs）are a very promising next-generation photovoltaic technology due to their excellent optoelectronic properties,solution processability,and flexibility.At present,the certification efficiency of organic-inorganic hybrid PSCs has reached to be 25.7%,which is basically same as that of crystalline silicon solar cells.However,the commercialization of organic-inorganic hybrid PSCs still faces great challenges because the low stability of the device caused by the decomposition and volatilization of organic components and the ion migration of metal electrodes.Substitution of organic cations by Cs⁺ions makes all-inorganic perovskite materials（CsPbX₃,X=I,Br,Cl）exhibit superior thermal stability,and carbon electrodes of PSCs can reduce the cost device degradation caused by metal electrodes because of the chemical stability,low cost and simply frabrication process.Therefore,all-inorganic carbon-based perovskite solar cells（C-PSCs）have gradually attracted attention.However,the current all-inorganic C-PSCs are relatively lagging behind the organic-inorganic hybrid PSCs.In order to improve the photovoltaic performance of all-inorganic C-PSCs,this thesis mainly focuses on improving the quality of all-inorganic perovskite thin films and optimizing the interface of the device.Specifically,defect passivation on the surface of perovskite films,controling crystal growth,properties of precursor solutions,and interface optimization between perovskite films and carbon electrodes have deeply and detailedly stuided.The relevant research contents and results are shown as follows:（1）In order to improve the quality of CsPbI₃ film,DMT-Cl was introduced to modify the surface of CsPbI₃ film through the post-treatment process.It is found that DMT-Cl can not only passivate the surface defects of CsPbI₃ films but also doping Cl into the films induces the secondary growth of CsPbI₃ crystals,eliminating pinholes on the surface of the films and promotes the growth of crystals to obtain large-sized grains.The effect of DMT-Cl on device performance was investigated.Finally,the efficiency of CsPbI₃ C-PSCs based on 2 mg/m L DMT-Cl post-treatment increased from 9.05%to 10.08%,the V_oc increased to 0.96 V,and the device was stored at room temperature and RH 10-20%environment for～600 hours,its efficiency can still maintain 60%of the initial efficiency,which significantly improves the storage stability of the device.（2）Additive and antisolvent engineering can effectively improving the quality of perovskite films.Therefore,we propose a synergistic approach,which is additive Pb（SCN）₂into ethyl acetate（EA）antisolvent,to tune the growth of CsPbI₂Br.Here,SCN^-in the additive Pb（SCN）₂ can promote the growth of crystals,and EA can effectively take away the residual precursor solvent and promote the diffusion of solutes and nucleation.After utilizing Pb（SCN）₂ and EA,large-sized grains and dense film morphology were obtained.Moreover,the producedPbS resulted from the thermal decomposition of Pb（SCN）₂ further passivated the surface defects of the CsPbI₂Br film.Compared to CsPbI₂Br C-PSCs without EA antisolvent or the synergistic method of Pb（SCN）₂ and EA,the efficiency of CsPbI₂Br C-PSCs modified by EA antisolve and synergistic effect of Pb（SCN）₂-EA increased to be 10.43%and 11.74%from 8.99%,respectively.（3）The properties of the perovskite precursor solution are closely related to the quality of the film.Therefore,thiophenedicarboxylic acid（T2AC）was added to the CsPbI₂Br precursor solution,and the properties of the solution were controlled by controlling the amount of T2AC.It was found that T2AC can promote the CsPbI₂Br precursor solution forms complexPbX₃^-andPbX₄^2-lead halide complexes,reducing the colloidal particle size and promoting the uniform nucleation of CsPbI₂Br.Secondly,T2AC can regulate the growth of CsPbI₂Br crystals due to the interaction of-COOH and S groups with Pb2⁺.When 0.3%T2AC is added into CsPbI₂Br precursor solution,the high-quality perovskite films with large grain size,good consistency,and low defect density are obtained,increasing the device efficiency of 13.62%from 10.92%,and producing V_oc of 1.26 V.（4）We design and synthesis of an asymmetric D-A type organic small molecule based on benzoic acid as the acceptor unit and 4,4’-dimethoxytriphenylamine as the donor unit,which is referred to MPA-BA.Improvement of the interface problem between CsPbI₂Br perovskite film and carbon electrodes by using MPA-BA as a hole transport layer（HTL）for CsPbI₂Br C-PSCs.The energy level barrier between the CsPbI₂Br film and the carbon electrode is reduced,and the-COOH and-OCH₃ groups at the end of the MPA-BA molecule effectively passivate the surface defects of CsPbI₂Br,improving the transport efficiency of hole carriers,reducing the carrier and recombination and energy loss.The highest efficiency of CsPbI₂Br C-PSCs based on the MPA-BA hole transport layer reaches 14.51%.When the thickness of the MPA-BA HTL is further increased,the device efficiency can still reach 13.48%,and the V_oc even reaches 1.28 V.