| Organic-inorganic hybrid perovskite materials are one of the most promising candidates for photovoltaic application due to their superior photoelectric properties,such as tunable bandgap,high carrier mobility and high defect tolerance.Currently,the record efficiency of perovskite solar cells(PSCs)has rocketed to over 25%.However,most of the high efficiency PSCs are based on solution processed perovskite films,which could introduce the formation of large amounts of defects during fabrication process,thus facilitating ion migration in the film and diminishing the performance and stability of PSCs.Meanwhile,the uncoordinated ions at the interface between perovskite and charge transport layers(CTLs)result in high interfacial defect concentration,which could encumber carrier transport and degrade the device performance.In this thesis,we developed a multifunctional route to reduce the defect concentration both at the bulk and the interface of perovskite films,regulating the interfacial energy structures,and finally improve the carrier transport in PSCs.The details are as follow:(1)Potassium doping-induced bulk phase stability enables stable and efficient PSCs.Potassium iodide(KI)was introduced into wide-bandgap perovskite films to suppress the ion migration.Experiment results reveal that the potassium cations(K+)can insert into perovskite lattice,blocking ion migration inside perovskite grains.Meanwhile,K2PbI4 could be formed at the grain boundaries by the reaction of KI and PbI2,thus passivating the grain boundary defects.Benefiting from this synergy effect,the photo-induced phase segregation of the film is effectively suppressed,giving rise to the significant reduction of the open-circuit voltage(Voc)deficit of the PSCs and thus the improved device performance.In addition,this KI doping route can be popularized to the PSCs with different bandgaps.(2)Interface regulation between perovskite and hole transport layer(HTL)by construction of 2D/3D perovskite heterostructure.Long chain alkylammonium bromides were introduced onto the 3D wide-bandgap perovskite surface to regulate the interface properties between perovskite and HTL.Experiment results reveal that the long chain alkylammonium bromides can react with PbI2,leading to the formation of 2D layered perovskite,which can effectively passivate the wide-bandgap perovskite surface.By finely controlling the alkyl chain length,the interfacial energy band structure between perovskite and hole transport layer(HTL)is optimized,which can improve the hole transport,giving rise to reduced interfacial charge accumulation.Consequently,the wide-bandgap PSCs with hexanelammonium bromide(HABr)modification achieved a champion PCE of 19.8%with an ultra high open-circuit voltage(Voc)of 1.31 V.More importantly,the HABr-induced hydrophobicity in the 2D layer can not only block moisture,but also retard migration of the alkali cations from the perovskites across the interface,eventually endowing the wide-bandgap perovskite based devices with a superior moisture stability.(3)Reconstruction of energy structures at buried interface by self-diffusion doping and robust onterfacial modifier.A self-diffusion interfacial doping by using ionic potassium L-aspartate(PL-A)was developed to restrain the carrier trap induced recombination by the reconstruction of energy structures at the buried SnO2/Perovskite interface.Experiments and theories certify that the PL-A anion will remain at the SnO2 surface as a surface dipole because of the strongly chemical adsorption after the perovskite film spin-coating while its cation will gradually diffuse to perovskite and form a N-doping,providing higher force and better match of energy level for the carrier transport.As a result,the efficiency delivered a 23.74%for the PL-A modified smallarea devices.The corresponding large-area devices(1.05 cm2)achieved an efficiency of 22.23%.Besides,the modified devices exhibited negligible hysteresis and enhanced ambient air stability exceeding to 1500 h. |
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