| The energy crisis is a biggest problem for human societies in the 21 st century.As we all know,solar energy is a renewable and clean energy.The utilization of sun to provide energy for power may resolve the energy problems faced by the human societies.Nowadays,various strategies for the conversion of solar energy have been developed.The highest conversion efficiency is achieved on the silicon-based solar cells to be25.6%,closing to the theoretical limit of 30%.However,the complicated production process and high production cost restrict the large-scale production and application of the silicon-based solar cells.In comparison to silicon,the organic/inorganic hybrid perovskite materials have excellent photovoltaic properties,such as suitable band gap,micron-level electron-hole diffusion length,extremely high absorption coefficient,high carrier mobility and so on.In recent years,the conversion efficiencies of perovskite solar cells have been improved from 9.7% to 22.1%,upon optimization of the device structures,materials and preparation process.However,the preparation of electronic transport layer(such as TiO2)in the perovskite devices requires calcination at high temperature(450oC),which increases the production cost and limits the commercialization of perovskite solar cells.Thus,it is important to fabricate the high performance perovskite solar cells without calcination of the electronic transport layer at high temperature.Firstly,this thesis reviewed the history and recent development of the perovskite solar cells,and introduced the experimental procesures for the preparation of perovskite solar cells and the strateigies for the improvement of its conversion efficiency.Then,the surface modification of fluorine-doped tin oxide(FTO)electrodes in thefabrication of perovskite devices was employed to improve the device photovoltaic performance.These strategies allowed the fabrication of perovskite solar cells at low temperature.The research content of this dissertation includes the following two parts:1.At 100 oC,a dense perovskite film was synthesized by combining one-step method and rapid crystallization method.A conversion efficiency of 9.0% was obtained on this film.The low conversion efficiency may be due to the huge energy barrier between FTO and the perovskite film inhibits the collection of electrons by FTO from the perovskite film.o-Dichlorobenzene was used to modify the FTO surface under UV irradiation to increase the work function.The deposited o-dichlorobenzene can effectively reduce the energy barrier of electron transport.The results show that the device under UV irradiation for 110 s has the optimized perovskite performance,with a photoelectric conversion efficiency of 13.4%,an open circuit voltage of ~ 1.0 V and a short circuit current density of 20.8 mA cm-2.2.Polyethylenimine(PEI)polymer was selected to modify the FTO electrode surface and served as an electron transport layer for the planar perovskite solar cell.The results indicate the amount of PEI is related on the performance of the resultant perovskite solar cells.The photovoltaic performance of the perovskite device fabricated from the PEI concentration of 0.04 wt% is the best,with the photoelectric conversion efficiency of 10.4%,the short-circuit current density of 20.09 mA cm-2 and the resistance of 9.97 ?.PEI improves the electron transport between FTO and the perovskite interface and reduces the device series resistance,facilating the collection electron by the FTO electrode.In summary,these studies in this dissertation indicate that the surface functionalization of FTO electrode surface with organic compounds could facilate the elctron transport between FTO and the perovskite films.Moreover,the fabrication processes at low temperature could simplify the structures of the perovskite devices.Furthermore,both strategies can improve the performance of the perovskite solar cells without calcination of the electronic transport layer at high temperature. |
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