The Optimization Of SnO₂-based Electron-transporting Layer Used In Perovskite Solar Cells

Perovskite materials have excellent optoelectronic properties such as solution processability,good absorption coefficient,excellent carrier mobility,long migration length,and tunable band gap.Therefore,it is widely used in solar cells,light-emitting diodes,and photodetectors.Since the advent of perovskite solar cells（PVSCs）in2009,after more than ten years of development,their power conversion efficiency（PCE）have increased from 3.8%to the current 25.7%.There are still problems such as poor repeatability,poor stability,large hysteresis,and high cost.These problems are mainly solved by exploring the composition ratio of materials,device structures and preparation process.Electron-transporting layer（ETL）is an important part of PVSCs,SnO₂ film has the advantages of high light transmittance,high electron mobility,wide band gap,simple preparation,and high stability for serving as ETL of PVSCs.However,SnO₂ ETL has the shortages such as high defect density and low electrical conductivity.This thesis mainly includes the modification of ETL for the conventional（n-i-p）structure PVSCs.The main contents are as follows:（1）We propose a solvent engineering method to prepare SnO₂ thin films by pretreating a conductive glass substrate（ITO）with hydrogen peroxide（H₂O₂）before spin-coating SnO₂ precursors solution.Pretreatment of ITO with H₂O₂ will increase the number of-OH on the surface of ITO and enhance the wettability of ITO,which is conducive to the rapid and flat spreading of SnO₂ solution on ITO glass.The prepared SnO₂ thin film is flat,dense and smooth,with less defect state density and better surface morphology.At the same time,the SnO₂ film with better surface morphology is conducive to the crystal growth of perovskite.PCE of the device prepared by H₂O₂pretreatment is as high as 19.84%,which is higher than that of the control device,which is 18.21%,and the stability of the device is also improved.The pretreated device can maintain 84%of its original PCE after 30 days of storage at room temperature with atmospheric enviroment.PCE of the control deviceonly retained79%.（2）Component engineering method:adding potassium tripolyphosphate(K₅P₃O₁₀)to SnO₂ precursors solution,K₅P₃O₁₀ is a stabilizer and chelating agent,which can form a bond with Sn,reduce the density of defect states,and contribute to a relatively smooth SnO₂ film.Moreover,K₅P₃O₁₀ is conducive to the crystallization and growth of the perovskite layer,and improves the interface contact between ETL and perovskite active layer.As a metal salt,K₅P₃O₁₀ has high conductivity.Doping can effectively enhance the electrical conductivity of SnO₂ thin films.PCE of the doped device is as high as 19.01%,while control one presents a PCE of 16.59%,and the stability of the device is also improved.The doped device can maintain 82%of its original PCE after 30 days of storage at room temperature with atmospheric enviroment.PCE of the control deviceonly retained 75%.（3）Interface engineering:N-phenyldiethanolamine was introduced as a passivation layer in the PVSCs of ITO/SnO₂/N-OH/perovskite/HTMs/MoO₃/Ag.N-phenyldiethanolamine can effectively form bonds with Sn to reduce the surface defect state density and the surface morphology of SnO₂ ETL.Moreover,N-phenyldiethanolamine has a positive induction effect on the perovskite,which is contributed to improving the crystallinity of the perovskite active layer and further improving device performances.PCE of the PVSCs based on N-phenyldiethanolamine is 19.02%higher than that of the control device（17.79%）.Device stability is also improved.The interface-modified device can maintain 90%in30 days at room temperature with atmospheric enviroment,while the retained PCE of the control device is only 81%.