Synthesis And Properties Of Mixed-halide Perovskite Solar Cells Based On Carbon Electrodes

Facing with the serious energy crisis and environmental pollution,developing and utilizing renewable energy to guarantee the sustainable development of human civilization,has become more and more important.Among the wind energy,tidal energy,geothermal energy,solar energy was the most valuable owing to its wide distribution,safety,environment friendly.Recently,perovskite solar cells have attracted considerable attention for their high carrier mobility,high light absorption and low exciton binding energy.The most extensive PSCs structure was fabricated by conductive substrate?FTO or ITo?,electron transport layer?compact layer,mesoporous layer or supporting layer?,perovskite layer,hole transport layer and electrod.The electron transport layer requires high electron mobility,low defect state,good light transmittance and appropriate band gap.The perovskite layer needs to obtain a compact and smooth thin film with large grain size.The hole transport layer needs to have high conductivity,close contact with the perovskite layer and the matched energy level.The electrode layer needs appropriately low chemical potential and high power function.The most commonly used electronic transport layer material is TiO₂ because of its suitable band position and stable chemical properties.The most commonly used perovskite material is CH₃NH₃PbI₃,and can be improved by doping the anion?I,Br,Cl?,cation?MA,FA,Cs?to optimize and improve the morphology and properties of perovskite thin films.The most commonly used hole transport layer material is organic small molecule material,but it is limited by high-cost,the poor stability.The most commonly used electrode material is metal electrode?Pt,Au,Ag?,but since Pt and Au are expensive and Ag is easily oxidized,metal electrodes are gradually replaced by other materials.Integrating the development background of the perovskite solar cells,in this paper,we have investigated the structure,morphology,preparation technology,mechanism and other aspects to improve the quality of perovskite film.In order to improve the efficiency of PSCs,the formation process of perovskite layer and the structural design of the perovskite solar cells have been studied.The main contents of this paper are as follows.?1?TiO₂ compact layer was prepared using hydrolysis of TiCl₄,TiO₂ nanorod arrays were synthesized by hydrothermal method,and investigated by XRD and SEM to characterize the crystal structure and morphology.?2?The CH₃NH₃PbI₃ perovskite precursor solution was prepared by adding CH₃NH₃I and PbI₂ into the DMF/DMSO mixed solvents.The main configuration of the PSCs in this section was FTO/TiO₂ blocking layer/TiO₂ nanorod arrays layer/CH₃NH₃PbI₃/spiro-MeOTAD/Ag.The samples demonstrated umbrella-shaped perovskite crystals with different crystal sizes and coverage areas.When the weight percent of the mixed solvent was too high,the perovskite crystal grain sizes decreased gradually accompanied with gradual emergence of pinholes between crystal boundaries,resulting in imperfect surface coverage.When the weight percent of the mixed solvent was too low,PbI₂ phase appeared.?3?The CH₃NH₃Pb(I_1-xBr_x)₃?x=0.1?0.15?0.2?0.25?0.3?perovskite precursor solution was prepared by adding CH₃NH₃I,PbI₂,CH₃NH₃Br,PbBr₂ into the 50 wt%DMF/DMSO mixed solvents.The main configuration of the PSCs in this section was FTO/TiO₂ blocking layer/TiO₂ nanorod arrays layer/CH₃NH₃Pb(I_1-xBr_x)₃/spiro-MeOTAD/Ag.The influence and microscopic mechanism of the crystal structure and energy level structure of perovskite layer were studied.The gradual substitution of Br ion for I ion has widened the bandgap of the perovskite layer,leading to the improvement of the open-circuit voltage of the device,thus improving the photoelectric conversion efficiency.When the x value was 0.2,CH₃NH₃Pb(I_0.8Br_0.2)₃,the photoelectric conversion efficiency of the device was the highest,up to 12.26%.?4?The effect of solvent engineering on the film quality and crystal structure of perovskite films was studied by using toluene,chlorobenzene and ethyl ether.When using ethyl ether,it can obtain the uniform and smooth perovskite thin film with complete coverage.The average conversion efficiency was 14.00%.?5?Investigation of the main configuration of FTO/TiO₂ blocking layer/TiO₂nanorod arrays layer/ZrO₂/CH₃NH₃Pb(I_0.8Br_0.2)₃/C.The energy level structure of the device was studied and the photoelectric properties and long-term stability of PSCs were tested.After 60 days of testing,the hole-conductor-free carbon-based PSCs showed excellent long-term stability,and the parameters were almost no attenuation within 60days.A large area?2.5 cm²?device was fabricated and the photoelectric properties were tested.