Study Of The Effect Of TiO₂ Nanorods Photoelectron Materials In The Organometal Halide Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells has attracted considerable attention due to their special properties, such as large absorption coefficient, electron-hole diffusion length and high charge carrier mobility. The power conversion efficiency?PCE? of perovskite solar cells has attained to 20%,which is comparable to that of the Si based solar cell. Furthermore, compared with silicon based solar cells, perovskite solar cells have the advantages of more simple preparation process, lower raw material prices, more extensive material sources and so on, which makes perovskite solar cell possess larger application potential.In general, the basic structure of perovskite solar cells is: FTO/ electron transfer material?ETM? layer / perovskite layer / hole transfer material?HTM? layer / metal electrode layer. Titanium dioxide?TiO₂?is the most commonly used electron transport material in the perovskite solar cells, and which is cheap, easy to produce, stable and friendly to the environment. The optimization of the structure and properties of TiO₂ can improve the photo induced electron injection efficiency, accelerate the photoelectron transport in TiO₂, and inhibit the composite reaction in the TiO₂ / perovskite interface so as to improve the performance of perovskite solar cells. In order to improve the transmission efficiency of the electron in the TiO₂ injection, one-dimensional TiO₂ nano materials, such as TiO₂ nanowires and array structure, TiO₂ nanotubes and TiO₂ nanorods, were used to replace TiO₂ nanoparticle mesoporous structure. Chemical elements were doped into TiO₂ nanocrystals to suppress the complex reaction, which reduce the oxygen vacancy TiO₂ surface, effectively inhibite the optical carriers recombination reaction of TiO₂ / perovskite interface.This thesis is divided into two parts: First, two kinds of TiO₂ nanorods?NRs? were prepared by two different reaction solvents. The perovskite solar cells were fabricated by using the two kinds of TiO₂ NRs as an ETM layer, respectively. The characteristics of TiO₂ NRs and their cells performance were investigated. Second, we synthesized successfully N/Zr-codoped TiO₂ NRs on FTO/TiO₂ seed layer by the hydrothermal method, which was further fabricated into the perovskite solar cells as an ETM layer. And their cell performance was investigated.In the first section,TiO₂ NRs were synthesized by the hydrothermal methods with ethanol-HCl?e? and water-HCl?w? solutions, respectively. MAPb I3-xClx perovskite solar cells were fabricated using the TiO₂ NRs as an ETM. The performance of the solar cells was optimized by changing the growth time of TiO₂ NRs. The photoelectric conversion efficiency?PCEs? of the best solar cells based on TiO₂NRs?e? and TiO₂NRs?w? are 8.6% and 11.8%, respectively. To explain this phenomenon, some investigations were performed. We can conclude that TiO₂NRs?w?appears a higher degree of order and alignmentthan TiO₂NRs?e?, and the thickness of perovskite capping layer in the cells based on TiO₂NRs?w?is more uniform than that on TiO₂NRs?e?according to the SEM test. UV-vis absorption spectra display TiO₂NRs?w?has a better optical propriety than TiO₂ NRs?e?. PL, TRPL, and EIS spectra indicate that the charge transfer for TiO₂NRs?w? is faster than TiO₂NRs?e?, while the charge recombination for TiO₂NRs?w? is more reduced than TiO₂NRs?e?. The PCE as high as 11.8% was achieved for the MAPb I3-xClx perovskite solar cells based on TiO₂NRs?w? by optimizing the parameters of TiO₂ NRs.In the second section, the physical and chemical properties of TiO₂ NRs doped with N or N/Zr were studied, of which the solar cells performance were investigated as the ETM layer. The effect of different doping concentrationsfor TiO₂ on the properties of perovskite solar cells was analyzed according to a series of experiments tests. Based on the SEM of TiO₂ mesoporous layers, it is found that chemical element doping does not affect the diameter of TiO₂ nanorods size, but affect the growth of the secondary structure of TiO₂ surface The ultraviolet visible absorption spectrum of the doped TiO₂ is obviously red shifted, and the band gap of TiO₂ semiconductor calculated according to the absorption intensity is narrowed with the doping of the chemical element. The analysis from the transient, steady-state fluorescence spectroscopy and the electrochemical impedance spectra indicated the doped TiO₂ has higher light electron injection efficiency.. Besides the electron hole recombination rate is lower in the interface between the perovskite and TiO₂. The perovskite solar cells with short circuit current of 20.74 m A/cm2, open circuit voltage of 0.89 V, and the PCE of 12.06% are achieved by optimizing the doping concentration of N/Zr in the TiO₂.