| The hybrid organic-inorganic perovskite materials have attracted considerable interest due to their salient optical and electronic properties,such as strong light absorption ability,small exciton binding energy,long carrier diffusion length,high carrier mobility,and have been widely used in photovoltaic field.The solar cells based on such materials have achieved the extraordinarily high solar-to-electric power conversion efficiencies(PCEs)as high as 22.7%.However,the uncontrollable crystal quality and interface stability extremely restrict the development of perovskite solar cells(PSCs).This study focused on the generation and separation of photogenerated charges in PSCs.From the perspective of perovskite quality regulation and interface design,the crystal defects in perovskite are reduced and the transmission of the photogenerated carriers at interface is improved,which effectively enhance the performance of PSCs.The cation with a suitable ionic radius was designed and filtrated to induced the intermediate phase by cation exchange.During the generation and consumption of the intermediate phase,the nucleation and growth of perovskite were simultaneously controlled without residue,and the mechanism of corresponding halide anion on perovskite crystal regulation was systematically studied.The high-quality perovskite film with enlarged grain size,prolonged photoluminescence lifetime,lowered defect density and increased carrier concentration was fabricated,which thereby improved the perovskite photovoltaic performance.Moreover,this method can be further extended to other mixed-cation perovskite systems.Additionally,the passivation layer was introduced at the inerface between perovskite and electron transport layer,which effectively prevented the chemical corrosion of the electron transport layer caused by degradation of the perovskite,protected the electrical properties of the electron transport layer,relieved the degradation rate of the perovskite crystal,improved the interfacial stability between perovskite and electron transport layer,promoted the efficient transport of the photogenerated charges at interface,and eventually enhanced the performance of PSCs.In order to improve the perovskite quality,the NH4+ with a suitable ionic radius was designed and filtrated to induced the intermediate phase by MA+(?)NH4+ cation exchange.(?)Regarding the formation of intermediate phase:the NH4+ with small ionic radius preferentially diffused into the[PbI6]4-octahedral layer to form NH4PbI3.Such NH4+ cations successfully occupied the cavity of lead coordination complexes which contributed to extra heterogeneous nucleation sites and reduced the defects derived from the absence of MA+.(?)Regarding the consumption of intermediate phase:during the annealing process,the highly crystalline CH3NH3PbI3 was formed by the cation exchange process between the MA+ and NH4+,instead of MA's directly entering.This successfully slowed down the crystal growth rate which effectively improved the perovskite quality with lowered defect density.For such protocol via introducing additive,the volatile NH3 as a by-product further facilitated the proposed phase transformation process.During the generation and consumption of the intermediate phase,we not only dexterously offset the inevitable differences of the nucleation rates for PbI2 and MAI,but also generate the highly crystalline perovskite film without residue.Through NH4+ induced phase transformation process,the extra heterogeneous nucleation sites and slowed-down crystal growth were simultaneously realized.Based on NH4+,the effects of Cl-,Br-and I-anions on perovskite crystal and PSCs were investigated.The Br-was successfully incorporated into perovskite by blending the nonsolute-cation-based NH4Br in perovskite precursor without change the stoichiometric ratio of Pb2+ and MA+ in perovskite precursor.The potential negative impacts on the perovskite crystallization,originated from the extra solute cations,were effectively avoided.The incorporation of Br effectively improved the phase stability of crystal structure and tuned the band gap.The introduction of Cl-by NH4Cl effectively enhanced the crystal quality.Through the density functional theory calculation,the passivation effect of negative-charged ion defects in perovskite materials by Cl-was studied,and the role of Cl-in perovskite material was further elucidated.By judicious adjusting the amount of NH4X(X=I,Br,Cl),the perovskite crystal quality was improved with the enlarged grain size of 804 nm,prolonged photoluminescence lifetime of 25.59 ns,lowered defect density of 4.53*1015cm-3 and increased carrier concentration of 9.67*1014 cm 3,and improved PCE of 10%.Such methodology of introducing the non-solute ammonium ion-based halide additive successfully provides guidance for the additive selection,the synthesis route design and even the novel synthesis reaction mechanism exploration for perovskite material synthesis,which probably inspires and enlightens researchers who work in related fields of PSCs.In order to improve the interfacial stability between perovskite and electron transport layer,the ultrathin Al2O3 film was innovatively inserted into the interface between perovskite and electron transport layer by atom layer deposition,and the regulation mechanism of Al2O3 film on the performance of PSCs has been in-depth studied.The introduction of the Al2O3 film at the interface between the perovskite and the ZnO electron transport layer,on the one hand,prevented the chemical corrosion of the ZnO electron transport layer by retarding the neutralization reaction with perovskite degradation product(HI),protected the electrical properties of the electron transport layer,and declined the degradation rate of perovskite;on the other hand,suppressed carrier recombination process at the interface,promoted the efficient transmission of photo-generated charges.In addition,the effect of passivation layer thickness on the light absorption property of perovskite was analyzed by FDTD optical simulation.The quantum tunneling model was used to theoretically predict the appropriate thickness of Al2O3 passivation layer.The performance of the PSCs could be modulated by tuning the thickness of Al2O3 middle layer,and the experimental results are consistent with theoretical results.Through tuning the thickness of Al2O3 layer deposited by ALD,the optimized PSCs performance was significantly increased by 44%at the thickness of 4 cycles.Therefore,the interface design protocol offers a promising new route to improve the performance of PSCs,which provides a promising approach for novel design of photovoltaic cells with commercial values.In this thesis,towards construction of photovoltaic devices with excellent performance,the quality control and interface design of the CH3NH3PbI3 perovskite crystal were realized.The regulation of non-solute ammonium cation and halide anions on the crystal quality of perovskite,and the passivation of ultra-thin Al2O3 layer on the interface between perovskite and electron transport layer,as well as their corresponding enhancement mechanism were in-depth studied,which effectively improved the performance of PSCs.Based on these studies,a further understanding of perovskite crystallization regulation and interface design is highly expected,which may give impetus to effectively promote the perovskite evolution. |
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