Research On Flexible Perovskite Solar Cells Based On Ultrathin Au Electrodes

Organic-inorganic perovskites are inexpensive,have a high light absorption coefficient,and have a diffusion length of electrons and holes of more than 1 mm.Therefore,organic-inorganic perovskites are ideal functional layer materials for solar cells,photodetectors,and light-emitting diodes.Organic-inorganic hybrid metal halide perovskite solar cells(pero-SCs)have become the focus of research due to their adjustable band gap,large carrier mobility,long carrier lifetime and low cost manufacturing processes.In recent years,the power conversion efficiency(PCE)of pero-SCs devices has increased rapidly,from 3.8% in 2009 to 23.3%,which is gradually equivalent to the efficiency of silicon-based solar cells.Mixed metal halide perovskite materials have been completely changed.The field of photovoltaic materials research.The pero-SC flexible device with long carrier transport distance and broadband light absorption is ideal for wearable devices and photovoltaic glass curtain walls,showing great potential applications.The problem of flexible solar cell devices is mainly concentrated on two aspects.One is the suitable flexible substrate,the roughness of the flexible substrate and the bending resistance,which affect the subsequent electrode flatness and the functional layer crystallinity of the device.The second is an electrode with superior performance.For solar cells,in addition to excellent electrical performance,the electrode must also ensure sufficient transparency.In addition,it must have excellent bending resistance for flexible devices.Conventional solar cells mostly use indium tin oxide(ITO)or fluorine-doped SnO2(FTO)as transparent electrodes,but they exhibit poor flexibility and mechanical stability,and cracks are easily formed in a bent state.Due to the poor mechanical stability of ITO,the efficiency of ITO-based flexible pero-SC decreases rapidly after repeated bending cycles.Carbon nanotubes,graphene,conductive polymers,titanium foil,silver mesh,silver nanowires and metal films have been reported as conductive electrodes for replacing ITO and FTO.In addition,an Ag-mesh / ploymer hybrid electrode was prepared by using a composite material in a PET substrate for pero-SCs.A translucent Ag back electrode based Pero-was fabricated on a titanium foil substrate.SC,enhancing the bending resistance of the substrate;using single-walled carbon nanotubes and single-layer graphene as flexible electrodes on the PEN substrate for pero-SCs.Although the conductivity and flexibility of non-ITO / FTO transparent electrodes have made great progress,the power conversion efficiency of ITO-free pero-SC is still much lower than that of ITO-based devices,which limits further applications.A metal film with high ductility and conductivity prepared by physical deposition techniques is one of the most promising electrodes.In order to increase the transparency of the visible light wavelength region to meet the requirements of the transparent electrode,the thickness of the metal thin film should be reduced below 10 nm,but the ultra-thin metal film is affected by the Volmer-Weber growth mode,the surface is rough,and the conductivity is poor.In this work,we used an ultrathin Au film with a 3 nm Ca seed layer combined with a SU-8 modified layer as an alternative to the ITO transparent electrode in flexible MAPbI3 pero-SCs.Due to the effective suppression of the Volmer-Weber growth mode by the SU-8 / Ca mixed modified layer,the ultra-thin Au film having a thickness of 7 nm exhibited an excellent smooth and continuous surface with a roughness of 0.556 nm.The ultra-thin electrode also has good optical and electrical properties with a sheet resistance of 14 ?/sq and a transmittance of 78% at 550 nm.In addition,the cured SU-8 modified layer with high flexibility can be peeled off from the hydrophobic substrate and used directly as a flexible substrate for pero-SC.The flexible MAPbI3 pero-SC with the prepared ultra-thin Au electrode prepared on the flexible SU-8 substrate achieved 11.44% PCE,which was only 17.2% lower than the ITO-based pero-SC,and the PCE was 13.81%..More importantly,the ITO-free flexible pero-SCs showed high resistance to bending and maintained an initial efficiency of 82% at a bending radius of 2.5 mm after 2,400 bending cycles.