In Situ Raman Spectroscopic Study Of CsPbBr₃ Perovskite Solar Cells

Perovskite solar cells（PSCs）have the advantages of high efficiency,low mass,low cost and simple fabrication process,therefore PSCs are of interest to researchers for a wider range of applications than other photovoltaic cells.In recent years,the focus of researchers on PSCs has been on the development of materials for the cell dense layer,electron transport layer,chalcogenide active layer and cavity transport layer in order to improve the performance of the cell.The photoelectric conversion efficiency of PSCs mainly depends on the modulation of carrier transmission path and interface.However,none of the existing characterization methods can achieve dynamic in-situ monitoring under the working state of PSCs,which greatly restricts the interface modulation aiming at performance improvement.In this thesis,two simplified structural models of Cs Pb Br₃PSCs were constructed（hole transport layers removed）,the morphology of the dense layer of titanium dioxide was altered,and its effect on the performance of Cs Pb Br₃PSCs was investigated by in situ Raman.One of the cells was a Ti O₂nanoparticles（TNPs）material prepared by conventional methods,with the structure of FTO/TNPs/Cs Pb Br₃/Carbon（hereinafter referred to as TNPs-CPB PSCs）;the other was a Ti O₂nanotube arrays（TNPs）prepared by anodic oxidation.In addition,Raman spectroscopy was used in conjunction with photovoltaic performance testing to perform in situ microscopic monitoring of the Ti O₂/Cs Pb Br₃interface between the two PSCs in the operating state.The operating mechanism of two kinds of PSCs in perovskite active layer was preliminarily studied.This study provided a new strategy to improve the photovoltaic conversion rate of PSCs.The main studies in this thesis were briefly described as follows:1.Preparation and in situ Raman spectroscopy of TNPs-CPB PSCsThe TNPs-CPB PSCs were first prepared and assembled,and then their morphology,structure and performance were characterized to confirm the structure of the material and the performance effectiveness of the PSCs.In particular,the TNPs-CPB PSCs were characterized by scanning electron microscope（SEM）to observe the formation of Cs Pb Br₃films on Ti O₂substrates,X-ray diffraction（XRD）to observe the crystal of Cs Pb Br₃films,UV-Vis diffuse reflection spectroscopy（UV-Vis-DRS）to characterize the UV absorption and band gap energy of the material;Photoluminescence spectrum（PL）to analyze the relationship between luminescence properties of Cs Pb Br₃films and laser wavelength,power and irradiation time was analyzed;Raman spectroscopy to analyze vibrational modes in the Cs Pb Br₃films and the optimal Raman excitation wavelength of 633 nm for the TNPs-CPB PSCs was optimized,and the Raman peaks were attributed to their sources;the homogeneity of the film preparation was assessed by Raman mapping.Secondly,the photovoltaic performance and Raman tests of the TNPs-CPB PSCs were carried out:（1）Current density-voltage（J-V）curve tests were carried out to ensure that the TNPs-CPB PSCs could work properly when the Raman laser was used as the excitation source.（2）The photostability of the cells was investigated.（3）The laser power was regulated to study the laser-dependent effects of the intensity and displacement of the Raman peaks(located at 83 cm^-1,127 cm^-1,144 cm^-1and 310 cm^-1),and it was shown that the peak intensity increased with increasing laser intensity.（4）The bias-dependent effects of the intensity and displacement of the Raman peaks were investigated by controlling the bias pressure,and it was shown that the peak intensity increased with increasing bias pressure.（5）The current-time（I-T）curves of TNPs-CPB PSCs were monitored,and it was observed that the cell had a significant photocurrent response to 532 nm excitation light,but no photoresponse to 633 nm laser.This part of the work presented a technique for monitoring the chalcogenide solar cells at the microscopic level and attributes the Raman peaks of the active layer,which laid the foundation for the investigations in the next chapter.2.Preparation and in situ Raman spectroscopy of TNAs-CPB PSCsTo verify the conclusions of the previous section and to further explore the cell performance enhancement strategies,we replaced the TNPs in the TNPs-CPB PSCs with TNAs to assemble cells with TNAs-CPB PSCs structure,and the test protocol was the same as in the previous section.The TNAs-Cs Pb Br₃interface was first physically examined using SEM,XRD,UV-Vis-DRS and PL and Raman single spectrum was collected,and found to contain Raman peaks of both titanium dioxide and Cs Pb Br₃.Next,in-situ Raman tests were carried out on the TNAs-CPB PSCs:（1）The cells were first tested for J-V curves to ensure that the Raman laser could be used as an excitation light source to achieve proper cell operation,and it was found that the performance of the cells containing the TNAs structure was superior to that of the cells containing the conventional Ti O₂dense layer.（2）The cell was continuously irradiated for 8 h using a xenon lamp to evaluate its stability,and the results showed that its photostability was excellent.（3）The laser power was tuned to investigate the laser-dependent effects on the intensity and displacement of the Raman peaks(located at 80 cm^-1,144 cm^-1,310 cm^-1,396 cm^-1,516cm^-1and 637 cm^-1),and it was shown that the peak intensity became larger with increasing laser and the peak position was less laser-dependent.（4）The bias-dependent effects of Raman peak intensity and displacement were investigated by regulating the bias voltage,showing that the peak intensity becomes smaller with increasing bias voltage and the peak position bias dependence was small.（5）The I-T curves of the cell were monitored,and it was found that the cell had a significant photocurrent response to 532 nm excitation light and also to 633 nm laser light,indicating that the TNAs expanded the photoresponse range of the cell and enhanced the absorption of visible light.