Application Of Sprayed Silver Nanowire Transparent Conductive Electrode In Perovskite Solar Cell

As the energy crisis and environmental pollution problems become more serious,the development of new types of clean energy is extremely important.Solar energy has become the most promising emerging energy technology due to its environmental protection,high efficiency and inexhaustible advantages.In recent years,perovskite solar cells have been rapidly developed due to their high efficiency,low cost,ease of large scale fabrication,and the ability to produce flexible and semi-transparent solar cells.Its power conversion efficiency（PCE）has rapidly increased from 3.8%in 2009 to the current 23.3%,and thus has great application prospects.However,ITO,which is often used as a transparent electrode of perovskite solar cells,has disadvantages such as high production cost,complicated production process,poor toxicity,and poor resistance to bending,which is not conducive to large-scale production.At the same time,high temperatures above 300°C are required during production of ITO,which also makes it unsuitable for the rapid development of semi-transparent perovskite solar cells.Silver nanowires are considered to be an ideal choice for replacing ITO transparent conductive electrodes due to their high electrical and optical transparency,good flexibility,and low temperature solution preparation.Spraying process is the preferred method for the preparation of silver wire because it is the simplest,the lowest cost method and suitable for large areas.However,due to the poor contact between the silver wires,the silver wire obtained by spraying coating cannot lead to the full use of the conductive ability of the silver wire.At the same time,there is a problem of poor adhesion between the silver wire and the substrate.In this paper,the inverted perovskite solar cells and sprayed silver nanowires are investigated.A transparent conductive composite electrode with high adhesion and low square resistance was obtained through the modification of the silver nanowires,and a high-efficiency,low-cost semi-transparent and ITO-free perovskite solar cell was successfully constructed.The specific content is divided into the following two parts:（1）Semi-transparent perovskite solar cells with spray coated silver nanowire（AgNW）top electrode and Ag NW/ZnO composite top electrode were fabricated and investigated.For the spray coated AgNW electrode,both sheet resistance（Rs）and averaged visible light transmittance（AVT,400-800 nm）decrease with the decrease of nozzle moving speed,which is ascribed to the increase of AgNW density of the electrode.A highest PCE of 13.27%with a low AVT of 16.3%was achieved for a cell having AgNW top electrode with a Rs of 15Ω/□.A thin layer of Zn O nano particles was coated onto the AgNW electrode,which was found to be able to decrease the sheet resistance of the Ag NW electrode.This is ascribed to the improvement the interconnection between AgNWs by filling the voids between AgNW wires.In the meanwhile,owing to the light scattering effect of ZnO nano particles,light transparence of the AgNW/ZnO composite electrode in the visible light range（400-800 nm）increases slightly after the deposition of ZnO layer.Both device performance and reproducibility of the perovskite solar cells are improved by using the AgNW/ZnO top electrode.A highest PCE of 11.13%with an AVT of 23.3%was achieved for a small area cell（0.09 cm²）,whereas PCE of 8.18%was also achieved for the cell with a large area of 1 cm².（2）The device performance of perovskite solar cells with the spray coated silver nanowires electrode,or the silver nanowires and sol-gel ZnO composite electrodes as the bottom electrodes was systematically studied.Based on the transparent silver nanowire electrode（square resistance 120Ω/□）obtained by spraying coating,the perovskite solar cell device with the structure of AgNW/PEDOT:PSS/CH₃NH₃PbI_3-xCl_x/PC₆₁BM/Al was fabricated.By optimizing PEDOT:PSS thickness,the device with a poor PCE of only 8.85%is obtained.The main reason is that the poor conductivity of sprayed silver nanowires leads to poor carrier extraction and conduction.At the same time,because the surface roughness of the silver nanowire is relatively large and the poor adhesion between the silver wire and the substrate results in poor film formation of the upper film and extremely easy formation of defect states between the interfaces,resulting in a low FF of the device.The adhesion between the silver wire and the substrate has been greatly improved,and its square resistance has also decreased significantly when a layer of sol-gel zinc oxide is spin-coated on top of the silver nanowire.This is due to the strong cohesion of the sol-gel zinc oxide,which promotes the contact between the silver lines and enhances the adhesion between the silver lines and the substrate.The surface roughness of the silver nanowire after spin-coated with sol-gel zinc oxide has also been significantly reduced,which is more conducive to the deposition of the upper film.At the same time,the Zn O film can effectively cut off the contact between the AgNW and the perovskite active layer,avoiding a chemical reaction between them,thereby improving the stability of the device.The performance and reproducibility of the perovskite solar cells obtained by using the silver wire and the sol-gel-zinc oxide composite electrode have been significantly improved,and an ITO-free perovskite solar cell with a PCE of 14.13%was finally obtained.