Crystal Growth And Composition Regulation Of Light Absorbing Materials In Mesoscopic Perovskite Solar Cells

Organic and inorganic hybrid perovskite with general structure AMX₃?A=MA,FA,Cs or Rb;M=Pb,Sn or Sr;X=Cl,Br or I?is a kind of direct semiconductor material.Perovskite has emerged as a new type of ideal semiconductor for photovoltaic and optoelectronic applications due to its strong light absorption,high carrier mobility,tunable bandgap,bipolar conductivity and solution processability.Recent years have witnessed a rapid development of perovskite solar cells?PSCs?,which has attracted worldwide researchers'interest.The certified photoelectric conversion efficiency?PCE?of lab-scale PSC has reached 22.7%,which has surpassed the multicrystalline silicon solar cell that lies in the leading position of the photovoltaic market.However,at present,the PSC with high PCE usually requires expensive organic materials as hole transporting materials and precious metals as counter electrode materials.Deposition methods used such as vacuum evaporation are also not cost-effective.In addition,the devices need to be prepared under inert gas?N₂?protection.This chanllegens PSCs'large-scale preparation and commercialization.We developed a printable,hole transport materials free,mesoscopic perovskite solar cell?MPSC?based on carbon electrode,aiming at simple fabrication and cost reduction.The introduction of 5-aminolevulinic acid?5-AVA?also made the unencapsulated device obtain the remarkable stability under continuous illumination for 1000 h.However,the tens-micrometer-thick mesoscopic scaffold without hole transport materials challenges the perovskite crystallization and carrier transport in the very thick mesoporous structure,which limits the further improvement of its efficiency.This thesis focuses on improving the crystallization of perovskite in mesoporous films through additive engineering and compositional engineering for high photovoltaic performance.The main content of the thesis consists of four parts as follows:Firstly,guanidine hydrochloride was used as an additive in MAPbI₃?DMF as solvent?.The device was fabricated by a simple and feasible one step process.After optimization,the voltage of the device was raised to 1.02 V,and a photoelectric conversion efficiency of 14.35%was obtained.The study showed that guanidine hydrochloride can act as crosslinking agent and optimize the morphology of perovskite?needle-like crystals decreased,massive or island-like perovskite crystals increased?.At the same time,it passivated the defect of the crystal,reduced the recombination and improved the device's performance.Secondly,the MAPbI₃ single crystal with a size of 8 mm was grown.At room temperature,a solvent free method was used to prepare the device in situ.The single crystal powder was located on the triple-layer mesoporous structure?TiO₂/ZrO₂/carbon?.Assisted with the dry CH₃NH₂ gas,the single crystal powder was dissolved into liquid and filled into the device.After optimizing the processing time of CH₃NH₂,the champion PCE of 15.17%was obtained.In the range of 4 ^oC³5 ^oC,and relative humidity among55%⁷5%,the device acquired the dark-state stability of 4500 h.Thirdly,FAPbI₃ has a phase transition between black and yellow phases.The black phase is an ideal optoelectronic material which is not easily obtained.In the mesoporous structure?more than 13?m thickness?,it is particularly difficult to generate the black phase.In a simple one-step method,we used DMF/DMSO as mixed solvent.Through the introduction of Cs⁺into FAPbI₃,the activation energy of conversion was reduced.Vapor-assisted annealing,it inhibited the volatilization of FAI,assisted phase transformation,and enlargred perovskite particles.Finally,the FAPbI₃ was stabilized in the black phase in the mesoporous structure,and a PCE of 15%was obtained,with absorption edge being widened to 840 nm.Finally,although lead-halide perovskite cells are expected to find important,large-scale markets,there will no doubt be applications where the soluble,toxic absorber material is not suitable and alternatives should be sought.SrCl₂ was introduced into Cs_0.1FA_0.9PbI₃ to partially replace lead.We found that SrCl₂ did not inhibit the phase transformation of FAPbI₃.On the contrary,it could increase the carrier lifetime.However,it showed a negative effect on the formation of uniform perovskite films,which reduced the extraction of carriers at the TiO₂ interface and decreased the cell efficiency.The performance of the device can be improved by continuing to optimize the doping amount of the non lead elements.