Stability Study Of MAPbI₃ Flexible Perovskite Solar Cells Based On Interfacial And Bulk Modification

Metal halide perovskites possess extraordinary optoelectronic and physical properties such as tunable band gaps,strong absorption coefficients,long carrier diffusion lengths,and low exciton binding energies,and are considered promising photoactive material candidates.Its low-temperature solution process（≤150℃）facilitated the development of flexible perovskite solar cells（F-PSCs）.Although F-PSCs has also achieved great success,it was difficult to meet the practical applications due to the problems of many defects at perovskite interfaces,lowly bending stability and water oxygen stability.Therefore,it was crucial to fabricate high-quality electron transport layers（ETLs）and perovskite light-absorbing layers on flexible substrates at low temperature for highly efficient and stable F-PSCs.In this paper,interfacial and bulk regulation and modification of the perovskites were taken to achieve the improvement of the performance and stability of F-PSCs.First,SnO₂ETLs were prepared by a low-temperature spin-coating processes,and the effects of the interface of substrates with different thicknesses and interfacial regulation of bilayer ETLs on the charge transport characteristics and photoelectric properties of F-PSCs were investigated.On this basis,the flexibility,oxygen and water barrier properties and charge transport properties of the MAPb I₃ perovskite layer were optimized by bulk modification to obtain the F-PSCs with excellent stability.The main research contents of this paper are as follows:1.SnO₂ETL was prepared by spin-coating process at low temperature（150℃）,and the effect of SnO₂ ETLs prepared with different concentrations（2.5～10wt%）on the formation of perovskite films and the performance of perovskite solar cells was investigated.By optimizing the concentration of SnO₂ precursor solution,dense and uniform perovskite films with large particle size and good crystallinity was formed,and the interface charge extraction and transmission are improved.The rigid device based on 7.5wt%SnO₂ ETLs achieved the PCE of 15.82%;and after storing for 600 h in ambient air without encapsulation,it still maintains 92%of the initial efficiency.At the same time,the properties of perovskite films and their corresponding devices based on SnO₂ ETLs treated at high temperature（450°C）and low temperature（150°C）were compared,and it was found that ETLs treated at low temperature had obvious advantages in optoelectronic properties.Finally,the flexible devices also achieved the PCE of 13.12%and retained 78%of the initial efficiency after 1000 bends at a bending radius of 3 mm.after storing for84 days in ambient air without encapsulation,it still maintains 48%of the initial efficiency.2.Different types of homojunction SnO₂ bilayer ETLs were constructed to improve the interfacial charge transport properties and hysteresis of devices based on the SnO₂ ETLs,and the differences between them and single-layer SnO₂ films and the performance of the corresponding devices were compared.Inserting a Sn Cl₂·2H₂O sol-gel layer（Cl₂-SnO₂）under the SnO₂ colloidal layer（Col-SnO₂）can form better interface contact,and the interaction between the two forms smooth and compact SnO₂ bilayer nanocrystalline structures with good interfacial contact and fewer interfacial defects between the perovskite layer,showing more excellent electron extraction and transport properties.The device based on the Cl₂-SnO₂/Col-SnO₂ bilayer structure showed the PCE of 15.01%.Compared with the devices with the Col-SnO₂ single-layer structure,the PCE of the devices based on the Cl₂-SnO₂/Col-SnO₂bilayer structure is improved by about 23.3%,the hysteresis is significantly suppressed and the device exhibits better stability.3.Conducting polymer（agarose）as additive and conductive polymer（agarose）/inorganic metal oxide nanoparticles（Ti O₂）as composite additive were investigated to improve the bulk quality of perovskite to further enhance the photovoltaics performance and stability of F-PSCs.The results showed that the agarose molecules will fill the voids of the perovskite films during the crystallization process,forming an organic network structure around the perovskite grains,making the perovskite films more compact,reducing the formation of defects and facilitating the transport of charges,while enhancing the hydrophobicity of the perovskite film.Ti O₂ nanoparticles can form a composite cross-linked network skeleton structure with agarose molecules,which further improves the long-term environmental stability and bending stability of flexible devices.The PCE of the pristine MAPb I₃ perovskite-based F-PSCs was 15.17%,and only 9.32%of the initial efficiency was retained after 1500 cycles of bending（bending radius of 3 mm）,and storage in ambient air without encapsulation for 36 days only retained 62.21%of the initial efficiency.While the AG-MAPb I₃ perovskite-based F-PSCs showed the PCE of 17.30%,retained 60.24%of the initial efficiency after1500 cycles of bending（bending radius of 3 mm）,and maintained 76.63%of the initial efficiency after 36 days in ambient air without encapsulation.The F-PSCs based on Ti O₂/AG-MAPb I₃ perovskite obtained the PCE of15.35%,and retained 63.48%of the initial efficiency after 2400 cycles of bending（bending radius of 3 mm）,and maintained 92.78%of the initial efficiency after 49 days in ambient air without encapsulation.