Low-cost High-efficiency Carbon-based Perovskite Solar Cells: Design,interface Regulation And Device Assembly Technique

The power conversion efficiency（PCE）of perovskite solar cells（PSCs）have rapidly increases from 3.8%to 25.7%,rivalling polycrystalline silicon solar cells.However,the most common-used hole transport layers（HTLs）as well as the energy-consuming electrode fabrication process both increase the fabrication cost of PSCs.Therefore,the replacement of the costly HTLs and noble metal electrodes would be a critical improvement for the industrialization of PSCs.The merits of carbon electrode such as excellent charge transfer characteristic,inherent stability as well as low energy consumption make it become a favorable choice to replace either HTLs and/or metal electrodes.Carbon-based perovskite solar cells（C-PSCs）are considered as one of the most promising types of PSCs for commercialization.Besides,all-air processed device assembly technique can further reduce the fabrication cost of C-PSCs.However,the absence of HTLs in C-PSCs leads to the mismatched band alignment and poor interfacial contact at the perovskite/carbon interface.Meanwhile,the crystallinity of the air processed perovskite film is low,resulting in high defect state density in perovskite films.Hence,to enhance the crystallinity of the air processed perovskite film,promote the charge transport between perovskite layer and transport layer,this thesis makes attempt on designing and optimizing the fabrication process of C-PSCs as well as modifying the interfaces between perovskite layer and transports layer.Details of research contents are as follows:（1）Phenethylammonium iodide（PEAI）is adopted as 2D spacer cation to fabricate 2D-3D（PEA₂Pb I₄-MAPb I₃）perovskite with a facile in-situ growth method.The growth of the 2D perovskite is confined at the grain boundaries to passivate the defect states at the perovskite grain boundaries.In addition,the energy band structure of the perovskite film is modified by the 2D perovskite which created a favorable energy band alignment between the perovskite layer and carbon electrode consequently promote the hole transport.Compared to the control and post-treated 2D-3D C-PSCs,the in-situ grown 2D-3D C-PSCs presents a superior PCE of 16.23%.Besides,the hydrophobic benzene ring of PEA⁺significantly enhanced the long-term stability of the device.The device retains 95.4%of its initial efficiency after been stored in ambient air condition（relative humidity at 20%-80%）for 60 days.（2）The bottom interfacial modification（BIM）strategy is developed to modulate the composition of the bottom of the perovskite films.FABr is introduced to the bottom of the perovskite films to modify the band alignment at the Sn O₂/perovskite interface consequently promotes the interfacial electron transport.Meanwhile,the crystallinity of the perovskite film is enhanced after the BIM treatment.The all-air processed HTL-free C-PSC fabricated by the BIM method exhibits an PCE of 16.20%.In addition,the BIM C-PSCs exhibit enhanced stability ascribed to the improved crystallinity of the perovskite films,and retains 81%of its initial efficiency after storing in ambient air condition for60 days.（3）An FAI solution penetration method is developed for further modifying the perovskite/carbon top interface.The penetrated FAI is able to react with the residual Pb I₂ at the perovskite grain boundaries to fill the gaps at the perovskite/carbon interface thus enhance the contact between these two layers.Combining the BIM method,dual-modified perovskite films exhibit further improved crystallinity and reduced trap state density.As a result,the dual-modified HTL-free C-PSCs with an architecture of ITO/Sn O₂/perovskite/carbon present a power conversion efficiency up to 17.49%in air.Moreover,the C-PSCs exhibit superior ambient stability maintaining 96%of its initial performance under storage in ambient air condition up to 60 days due to the carbon electrode being filled by the penetrated FAI against the moisture erosion.（4）We develop flexible HTM-free C-PSCs with enhanced flexibility and light utilization by implanting carbon nanotubes（CNTs）into perovskite film and carbon electrode to boost the connection at perovskite/carbon interface as well as by coating a polymethyl methacrylate（PMMA）antireflection layer to increase the transmittance of the polyethylene naphthalate/indium tin oxide（PEN/ITO）substrates.The CNTs are proven to not only enhance the flexibility of the devices,but also facilitate charge extraction and transport at perovskite/carbon interface.The average transmittance of the PEN/ITO substrates increase by 3.63%after the incorporation of PMMA antireflection layer.As a result,the flexible HTM-free C-PSC with an architecture of PMMA/PEN/ITO/Sn O₂/MAPb I₃/carbon presents a power conversion efficiency（PCE）of 14.44%,which is the highest PCE for flexible HTM-free C-PSC devices.Moreover,this flexible PSC retains more than 84%of the original PCE after bending 1000 cycles at 7 mm bending radius attributed to the enhanced connection at the perovskite/carbon interface.