The Research Of Surface/Interfacial Regulation And Defect Passivation Of Perovskite Solar Cells

Based on the optimization of surface/interface of perovskite and device preparation,the certified power conversion efficiency(PCE)of perovskite solar cells(PSCs)has exceeded 26%.The advantages of low-temperature solution-processing,flexible fabrication and applicable tandem devices make PSCs the most potentially efficient and low-cost photovoltaic devices.However,high defect density and activity as well as unsatisfactory interface characteristics,lead to large energy losses and instability of devices.Defects,especially at the surface,could decrease carrier mobility,diffusion length,and lifetime of perovskite through charge scattering and trapping.Defects could interact with environmental molecules to cause degradation of perovskite materials and devices.The accumulated defects at the interface between perovskite and charge transport layer cause energy-level mismatch and interface charge accumulation,affecting built-in electric-field and stability of devices.Herein,the influence mechanism of defects on the photophysical properties,and stability of perovskite as well as interface charge transfer and stability of devices is systematically investigated.From the perspective of crystallization modulation,dimensional design and surface-treatment,effective approaches for interface defect and energy-level manipulation are designed.The manipulation mechanism of multi-ligand molecules on perovskite defects and interface is elucidated,and gradient bandalignment are constructed to facilitate charge transfer.The photo-induced halide phase separation,Sn2+ oxidation,and ion migration are significantly inhibited.Interface charge transport dynamics and device stability are synergistically improved.The main research contents are as follows:(1)The grain boundaries and surface dual-regulation of CsPbI2Br perovskite are achieved through formamidine salt additives and surface-treatment.The effect mechanism of dualregulation on open circuit voltage(Voc)and stability of devices is systematically studied.Under the chelation coordination between formamidinethioureide additives and perovskite,the nucleation and growth regulation endow dense CsPbI2Br films with large grains over 2 μm.The shallow-level iodine vacancy(VI)and deep-level lead iodide antisite(PbI)defects are effectively passivated,and the formation of deep-level lead clusters(Pb0)are inhibited.The regulatory mechanism of surface-treatment,formamidine bromide on interface defects and energy levels is revealed.The cation exchange realizes the Br-rich layer and constructs gradient energy level arrangement at the CsPbI2Br/Spiro-OMeTAD interface,thus promoting hole transport and electron departure.The defect-assisted non-radiative recombination is effectively suppressed,and interface charge transfer is significant improved.The device achieved a PCE of 16.74%with a high Voc of 1.34V,and the hysteresis effect was significantly reduced.The phase transition and photo-induced phase separation are inhibited by defects suppression and Br-rich surface formation,and thus enable devices with excellent humidity and light stability.(2)1D perovskites with intermolecular π-π stacking and edge-shared[MI6]4-octahedra are synthesized by organic conjugated spacer molecule,4-Aminobenzamidine dihydrochloride.1D/3D Sn-Pb perovskite structure with high stability and efficient charge transport are constructed.The effect mechanism of 1D perovskite on crystallization,defects,photoelectric properties,and structural stability of Sn-Pb perovskite is systematically studied.1D perovskites with intermolecular π-π stacking are self-assembled on the substrate,providing nucleation sites for perovskite crystallization and thus endowing perovskite films with low defects and tensile strains.After the formation of perovskite film,1D perovskites self-assembled at the grain boundary of perovskite/charge transport layer interface to in-situ encapsulate the 3D perovskites.π-π stacking Organic spacer cations provides an ordered channel for charge transport,passivates defect sites and stabilizes surface Sn-I octahedral,thus effectively inhibiting Sn2+ oxidation and I-ion migration are effectively inhibited.Then the carrier lifetimes and surface potential homogenerity are greatly ehnaced.Consequently,the built-in electric-field and Voc of devices are greatly enhanced.The devices achieve a PCE of 22.23%,and the hysteresis is significantly reduced.The suppressed ion migration and hydrophobicity improvement endow the devices with excellent storage and light stability.(3)A surface reconstruction strategy for Sn-based perovskite films is designed using 6maleimidohexanehydrazide trifluoroacetate(MHATFA)/isopropyl alcohol(IPA)surfacetreatment.The effect mechanism of MHATFA on surface defects and energy-level at the perovskite/C60 interface was systematically studied.For one thing,MHATFA can protect FASnI3 films from the damage of IPA solvent,and achieve surface polishing of FASnI3 film.The hydrazide and carboxyl(C=O)groups realize the passivation of Sn-related defects(Sn4+,VI,Sni,SnI)and enhance the oxidation barrier of Sn2+.The surface potential homogeneity and carrier lifetimes are greatly enhanced.For another,the enhancement mechanism of charge transport dynamics at the perovskite/C60 interface is illuminated.The surface dipole formation(C=O…Sn2+)induces an up-shifted Fermi-level at the shallow surface,and forms a grade heterojunction favorable for electron transport and hole departure.As a result,the devices achieve a PCE of 13.64%with negligible hysteresis.Moreover,the more stable and ordered surface enhance the excellent humidity and light stability of devices.The mechanism of inhibiting Sn-and I-related defects on stability enhancement of Sn-based perovskite and devices is illuminated.(4)Aiming at relieved p-type doping an instability caused by surface defects,the cooperative surface-treatment of imidazole and trifluoromyloxime salt is designed to achieve compensation(VFA,VSn)and passivation(ISn,IFA,Sn4+)of surface defects which are related with surface p-type doping.The effect mechanism of surface defect regulation on carrier mobility and lifetime,surface potential,and energy-level of Sn-Pb perovskite is systematically studied.The internal relationship between surface defects and band structure is studied,and the interfacial energy-level barrier is reduced.Encouragingly,the relived p-doping enhances the carrier lifetime(7.12 μs)and electron mobility.Surface energetic transformation induces a n-n+homojunction and thus back-surface electric field which promotes electron extraction and inhibits interface charge recombination.The minority carriers and band offset at perovskite/C60 interface are greatly reduced,and the built-in electric field of the devices is greatly enhanced.Consequently,the devices deliver a PCE of 22.05%with greatly reduced hysteresis.The enhanced barrier of I-ion migration and Sn2+ oxidation endow the devices with excellent storage and light stability.