The Effect Of PbI₂ Films Microstructure On The Light Harvestor Layer Of Perovskite Solar Cells And Its Temperature Dependent Performance

In the organic / inorganic hybrid perovskite solar cells research, the microstructure regulation of CH₃NH₃ PbI₃ layer is an important topic. The power conversion efficiency of perovskite solar cells is not only relating to the light absorber performance, but also the collection efficiency of photo generated carriers. The collecting capability of carrier depend on the transfer and recombination process. The microstructure of CH₃NH₃ PbI₃ layer is an important factor in that process of the device. During the two-step process which prepared CH₃NH₃ PbI₃ light-absorbing layer, the light-absorbing layer is formed by the reaction between PbI₂ films and CH₃NH₃ I, therefore the microstructure of PbI₂ films will have a major impact on the microstructure in light absorbing layer.In this paper we prepare the PbI₂ films by spin-coating method, and fi nd that the microstructure of PbI₂ films can be significantly regulated by n-butanol addition in the solution spin coating process. Introducing 5 v/v % n-butanol additive to prepare PbI₂ layer with a mesoporous structure, is useful to the reaction between the pore and CH₃NH₃ I. We can find that the addition of n-butanol solvent increases the CH₃NH₃ PbI₃ size of grains by Scanning Electron Micrograph. Incorporating the XRD of a sample we can see, without changing PbI₂ films crystal structure, the addition of change CH₃NH₃ PbI₃ films crystal structure significantly. I-V tests show that open-circuit voltage Voc and the power conversion efficiency of the solar cells typical perovskite device PCE compared with the control device has improved by adding a solution of n-butanol solvent PbI₂, respectively, from 13.8% to 15.6% and from 1.006 V to 1.096 V. Impedance measurements show that butanol complex additive may increase the recombination resistance of the device and reduce the photo recombination rate of generated carrier recombination rate, the transmission resistance of device interface is also decreased at same time, which is help for the interface charge collection process. In photoluminescence measurements, CH₃NH₃ PbI₃ films with n-butanol additive has a stronger fluorescence emission, indicate that the defect density in films decrease, while the fluorescence quenching degree CH₃NH₃ PbI₃ films on Ti O2 electron transport layer is also enhanced, indicating charge transfer process during interface can be improved.On the other hand, this paper also explores the capacitance characterization of mesoporous perovskite solar cells, the capacitance method and I-V measurement are very important means of device characterization. In this paper the CV method and variable temperature admittance spectroscopy methods are also used, which two play important roles in the research process Si, CIGS solar cells, but the application is perovskite devices is still relatively rare. In this thesis, CV measurements to study the doping concentration of mesoporous perovskite devices, interface barrier and depletion layer width. We got its defect activation energy. We also understand the situation of the defect distribution, and the obtained defect energy distribution exhibits a broad spectrum with the maximum at 240 me V. This work showed that C-V method and variable temperature admittance spectroscopy can be used as a powerful tool for perovskite solar cells research device.