The Preparation And Performance Research Of Carbon-based Hole-transport-layer-free Perovskite Solar Cells Under Atmospheric Environment

With the development of new semiconductor materials,organic-inorganic hybrid perovskite solar cells have attracted considerable attention due to the optoelectronic properties,and the efficiency has rapidly optimized from an initial 3.8%to over 25%.Methylammonium lead tribromide（MAPb Br₃）-based perovskite solar cells（PSCs）have been versatilely used in water electrolysis,electrocatalysis,multi-junction solar cells and light emitting diode due to the wide band gap and better stability against water,light and heat.However,the commercial application of PSCs should be synthetically considered among the PCEs,production cost,preparation process,stability and environmental friendliness.Taking the above factors into consideration,we tried to prepare highly efficient,stable,preparative simple and environmentally friendly carbon-based hole-transport-layer-free（HTL-free）MAPb Br₃ PSCs under atmospheric environment.In this thesis,three aspects of film-forming engineering,rare earth doping and passivation strategies are discussed to effectively optimize the crystal properties of the perovskite phase and further promote the PCEs and stability of the PSCs.By optimizing the perovskite absorber layer,the average PCE of the PSCs has been improved from 3.74 to 9.77%,together with an increase of the open-circuit voltage(V_OC)from 0.99 to 1.67 V.The main research contents are as follows.Firstly,the film-forming engineering of the MAPb Br₃ perovskite absorber layer was improved by precursor process,carbon-based HTL-free perovskite solar cell with the structure of FTO/c-Ti O₂/m-Ti O₂/MAPb Br₃/Carbon was prepared by an optimized two-step sequential deposition method under an atmospheric environment.MA components and Br ions will escape from MAPb Br₃ perovskite crystals during annealing,resulting in the formation of vacancies and uncoordinated Pb²⁺on the surface of perovskite.Pb²⁺will become the carrier recombination center,which severely limits the device performance.Therefore,adding 20%MABr into Pb Br₂precursor solution can effectively reduce MA vacancies and uncoordinated Pb²⁺defects.The addition of MABr promoted the complete conversion of Pb Br₂ into MAPb Br₃ perovskite,resulting in improved grain growth,reduced defect density,and a denser and better crystallinity of MAPb Br₃ layers,which further ameliorated the uncontrollability of perovskite grain size and surface morphology in the traditional one-step and two-step methods.After optimization,the maximum PCE of the PSCs reached 7.64%.Secondly,we further optimize the perovskite absorber layer on the basis of a precursor engineering method.By modulate the MAPb Br₃ perovskite lattice through rare earth doping,the grain size and surface roughness can be improved.This strategy reduces the defects density and inhibits the non-radiative recombination of perovskite films,bringing a remarkable increase in performance of devices.We incorporated Y³⁺ions into MAPb Br₃ lattice,the ionic radius of Y³⁺ions is much smaller than Pb²⁺ions,the contraction of lattice leads to the enhancement of the reciprocity between Pb²⁺and Br^-,which increased the tolerance factor of perovskite lattice and improves the phase stability.At the same time,with the incorporation of Y³⁺ions,the defect density and non-radiative recombination of perovskite films were decreased,thus the device exhibited superior photovoltaic performance.At an optimal concentration(doping 2%Y³⁺),Y³⁺-doped MAPb Br₃ PSCs achieved a PCE of 8.31%and the V_OC of 1.56 V.Then,in order to find a method to prepare perovskite films with low production cost,good repeatability and high performance and stability,rare earth ions were replaced by bifunctional-molecule 3-chlorobenzylamine（3-CBA）additive.The introduction of 3-CBA additive into the perovskite precursor solution affected the growth kinetics of perovskite crystals,the defect density and the non-radiation recombination were suppressed in perovskites by using 3-CBA additives to control the speed and orientation of crystal growth.Then the perovskite films were treated with 3-CBA additive to further passivate the defects of the surface.The perovskite films were effectively resisted H₂O and O₂ in air by double passivation of bulk and surface defects of the perovskite layer,which improves the long-term stability of the device.After 3-CBA treatment,the PCE of the device was increased from 6.29%to9.55%,with the V_OC of 1.6 V and the fill factor of 0.76.Finally,in order to enhance the performance and stability of PSCdevice,surface passivation process is used to modify the interface between the perovskite film and the carbon electrode.On the basis of 3-CBA body passivation,we utilized phenylethylammonium bromine（PEABr）to treat the MAPb Br₃ perovskite film.On the one hand,the PEABr can effectively passivate the uncoordinated ions of the perovskite film and resulting in the uniform and compact morphology of MAPb Br₃films with low trap density.On the other hand,it can improve the energy level arrangement,which is conducive to the hole extraction between perovskite layer and carbon electrode,resulting the recombination suppression and high efficient PSCs.Finally,the V_OC of device based on carbon-based HTL-free MAPb Br₃ perovskite cells improved from 1.60 V to 1.67 V and achieved a PCE of 9.77%.At the same time,the hydrophobic benzene ring on the surface passivator can effectively block water and oxygen,thus slowing down the decomposition of the perovskite film and improving the long-term stability of the device.