Research On Key Functional Materials In Monolithic Perovskite/Silicon-heterojunction Tandem Solar Cells

Due to the rational distribution and adequate utilization of solar spectrum,moreover,a higher open circuit voltage can be achieved,perovskite/silicon-heterjunction?SHJ?tandem solar cells make it possible to overcome the theoretical conversion limitation of silicon-based single junction solar cells.However,a compatible fabrication process of PSC as well as SHJ solar cell is required in order to meet their series structure,that is,the top perovskite cell prepared on the SHJ bottom cell will be restricted by some technological conditions as following.Firstly,light illuminated from the top perovskite cell,so the original opaque metal electrode needs to be replaced by a transparent electrode.Secondly,the passivated hydrogen in SHJ cell will be released from the cell over 200°C high temperature and then deteriorate the device performance.So,the charge transport layer in the top perovskite cell must be prepared at low temperature.Thridly,in order to improve the performance dramatically,the light absorbance and transmittance of perovskite in perovskite/SHJ tandem solar cells should be designed carefully thereby,reaching to the same short-circuit current between the top and the bottom cell,considering that the output current of the tandem cell is limited to the minimum short-circuit current in the sub-cells.Fourthly,the SHJ has good stability,which requires that the perovskite solar cell needs good stability to ensure the long-term operation.In this thesis,we studied the key functional materials applied to the perovskite/SHJ tandem solar cells based on these constraints.It mainly focused on the following aspects:the preparation of SnO₂ charge transport layer by low temperature solution method,ultra-thin gold and ITO transparent electrode preparation,solvent engineering to balance the light absorbance and transmittance in perovskite for tandem solar cells.The details are as follows:?1?We have explored a method of preparing SnO₂ electron transport layer through SnCl₄ hydrolysis process,which utilizes anhydrous SnCl₄ as tin precursor,ethanol as solvent and water as oxidant.It was found that the morphology and photoelectric properties of SnO₂ film can be modulated by adjusting the ratio of water to the solution.Through the optimization of deposition process,efficiency of planar perovskite solar cell has been improved up to 17.38%.It is proved that low temperature prepared SnO₂ charge transport layer can make perovskite solar cell with excellent photoelectric conversion performance,and it can be applied to perovskite/SHJ tandem solar cells.?2?The ultrathin metal gold electrode prepared by thermal evaporation method is used as transparent electrode.The optical and electrical properties of ultra-thin gold thin films at different thicknesses have been studied.The near infrared semitransparent perovskite cell has been successfully prepared and combined with the SHJ cell to form two-teminal tandem solar cell with MoO_x thin film as the antireflection layer.Finally,a tandem cell with an efficiency over 10%and an open circuit voltage of 1.7 V is obtained.We also prepare MoO_x/ITO transparent electrode.We modify the thickness of buffer layer and sputtering power of transparent electrode for equilibrium between protection of underlying layers and conductivity of electrode.Furthermore,thickness of ITO transparent electrode is varied to realize the optical optimizations.Ultimately,we obtain a monolithic perovskite/SHJ tandem solar cell yielding the matched short circuit current density of up to 15.11 mA/cm² measured without any anti-reflective film.?3?We have employed caesium formamidinium?Cs/FA?lead halide perovskite as top cell prepared with pure N,N-dimethyl formamide?DMF?,pure dimethyl sulfoxide?DMSO?and their mixtures with different ratios of volume.With the increment of DMSO in mixed solvents,the effect of different solvents on the surface structure and photoelectric properties of perovskite materials for tandem solar cells was systematically examined.When the volume fraction of DMSO in mixed solvent is 40%,we can obtain a smooth,good passivation effect,high-quality perovskite film.Most importantly,the light absorbance and transmittance is up to a balance by applying the perovskite film in the tandem solar cells,which leads to a reverse scanned power conversion efficiency over 20%and better stability.