Light-absorbing Layer Modification And Interface Modulation For Perovskite Solar Cells

Based on the national strategic goals of carbon peaking and carbon neutrality,developing green and low-carbon new energy technologies is an important initiative to promote energy transformation and high-quality development.As one of the sustainable clean energy sources,photovoltaic technology has been booming in recent years.Among them,perovskite solar cells(PSCs)have rapidly emerged as leading competitors in the photovoltaic field owing to low cost,easy preparation process,and excellent photovoltaic conversion performance,which have attracted widespread attention in academia and industry.The certified efficiency of PSCs has exceeded 26%,although there is still a gap from the Shockley-Queisser limit especially the severe nonradiative recombination causing high open-circuit voltage(VOC)loss.In addition,the commercial application of PSCs confronts stability challenges.The soft ionic lattice results in numerous charged defects within 3D perovskite film,which are not only the nonradiative recombination centers but also trigger perovskite degradation under the stimulation of external environment.Furthermore,the interfaces between perovskite layer and charge transport layers are also rich in defects.And the interface properties greatly affect the carrier transport and recombination processes.Therefore,it is of far-reaching significance for fabricating efficient and stable PSCs by in-depth investigation into the mechanisms of additives and interfacial modifiers on perovskite photovoltaic properties,and rational design of perovskite microstructures to overcome the serious nonradiative recombination and instability issues.Herein,from the perspectives of perovskite bulk optimization and interface modification,additive strategy and interface post-treatment method are adopted to optimize the defect property and carrier behavior of perovskite film through the modulation of intermolecular interactions,so as to realize simultaneous enhancement of device performance and stability.The main research contents are as follows:(1)Pseudohalide thiocyanate(SCN-)was employed to inhibit oxidative degradation of Sn2+to Sn4+,and its effects on photovoltaic performance and stability of mixed Sn-Pb PSCs were investigated.The results show that the incorporation of KSCN significantly improves the crystallization quality of FA-based mixed tin-lead perovskite films and prolongs the carrier lifetime.SCN-,with an ionic radius similar to that of iodide ion,is able to occupy the X-site in perovskite lattice.The coordination interactions between Sn2+and SCN-heal the undercoordinated Sn2+and restrain the formation of Sn vacancies.DFT calculations indicate that the addition of SCN-increases the adsorption energy of oxygen on perovskite surface,thereby inhibiting Sn2+oxidation and alleviating the p-type self-doping caused by oxidation.It reduces defect density and nonradiative recombination losses,and also helps to improve the charge transport property at the perovskite/electron-transport layer interface.Ultimately,the power conversion efficiency(PCE)of FASn0.5Pb0.5I3-based PSCs was enhanced by 14.5%to 13.74%,and device stability was also significantly strengthened.(2)2D/3D PSCs were constructed based on multiple-ring aromatic ammonium 1naphthalenemethylammonium(NMA),and the electron acceptor molecule 1,2,4,5tetracyanobenzene(TCNB)was further utilized to improve the charge transport property.It is found that the TCNB molecule with high electron affinity can trigger intermolecular π-πinteractions,which heightens structural rigidity and simultaneously decreases the exciton binding energy of low-dimensional phase.Meanwhile,as an electron acceptor molecule,TCNB achieves p-type doping effect on perovskites,optimizing the energy level alignment at the perovskite/hole transport layer interface and thus promoting hole carrier transport.In addition,HRTEM results demonstrate that 2D phases are distributed at grain boundaries of 3D perovskites,which diminishes defect density.As a result,the carrier lifetime is prolonged and trap-assisted nonradiative recombination is suppressed.Consequently,the champion device based on 2D/3D perovskite achieves a PCE of 24.01%.The environmental stability of 2D/3D perovskite devices is also notably improved due to the increased hydrophobicity and reinforced lattice structure.(3)A-site cation alloying at perovskite interface was achieved by a post-treatment strategy with organic ammonium halide s-methylthiouroniumiodide(MTUI)to construct a 1D/3D perovskite heterostructure.It is shown that MTUI can react with residual lead iodide in perovskite films to form 1D perovskite chains with face-sharing octahedra.By virtue of hydrogen bonding between=NH2+and I-and the coordination between S and Pb2+,MTUI posttreatment repairs VFA defect on perovskite surface and inhibits the formation of VI,so that defect density is obviously reduced and nonradiative recombination is greatly restrained.In addition,MTUI post-treatment increases the work function of perovskite,which is beneficial for charge transport at the interface of perovskite/hole transport layer.As a result,the VOC of PSCs is increased from 1.09 V to 1.17 V,and the PCE is up to 24.37%.Besides,the face-sharing octahedra in 1D chains enhance thermal stability of perovskite films and prevent the ion migration behavior,so the stability of MTUI post-treatment device is accordingly improved.(4)The post-treatment strategy was improved by molecular engineering of organic spacers,which synergistically modulated the interactions among ammonium ligands,isopropanol solvent and perovskite and elucidated the influence mechanism of functional group in organic spacer on interfacial passivation effect.Cyano group in p-cyanophenethylamine hydrochloride(CPEACl)attracts more electrons than the fluorine in p-fluorophenethylamine hydrochloride(FPEACl),which not only helps CPEACl bond with isopropanol but also promotes bonding between CPEA and perovskite after post-treatment.The hydrogen bonding between cyano and hydroxyl restricts hydroxyl activity in isopropanol,mitigating solvent dissolution damage to underlying 3D perovskite and thus decreasing ligand penetration.The stronger electronwithdrawing ability of cyano also enhances the bonding strength between-NH3+ of CPEACl and[PbI6]4-octahedron,which magnifies physical and chemical passivation effects on perovskite.CPEACl post-treatment reduces the Young’s modulus of perovskite film,alleviates residual tensile strain through lattice reconstruction,and repairs FA vacancies simultaneously.As a result,the champion device achieves a PCE of 24.76%with a VOC of 1.18 V.The hydrophobicity and steric hindrance effect of organic spacers also greatly strengthen the environmental stability of perovskite films and devices.