Research On Performance Improvement Of Perovskite Solar Cells Based On SnO₂ Electron Transport Layers

Perovskite solar cells（PSCs）first appeared in 2009,their photoelectric conversion efficiency（PCE）has improved from 3.8%to 25.7%rapidly.Organic-inorganic hybrid perovskite materials have excellent properties,good absorption coefficient,long charge diffusion length,controllable band gap and solution processability.SnO₂electron transport layers（ETLs）and perovskite light-absorbing layers are prone to cause poor crystallinity and much surface defects during preparation.In this paper,SnO₂ETLs were treated with four solvents by hydrothermal and solventhermal method,octadecyltrichlorosilane(C₁₈H₃₇Cl₃Si,Octadecyltrichlorosilane,OTS)was used for interfacial modification between ETLs/perovskite layers,and five different antisolvents were used for preparing perovskite layers.The effects of different processes on the photoelectric performance of PSCs were investigated.The specific study and findings are as follows:（1）SnO₂ETLs were prepared by sol-gel method,the hydrothermal and solventhermal treatment solutions were deionized water,methanol,ethanol,and isopropanol,respectively.The effect of hydrothermal and solventhermal treatment on the photoelectric performance of SnO₂films and PSCs was studied.The optical transmittance of SnO₂was enhanced by hydrothermal solventhermal treatment of the films,the surface contact angle was reduced,and the photoelectric performances of PSCs were all enhanced.Hydrothermal treatment can increase the size of SnO₂grains,reduce the film roughness,improve the crystallinity of SnO₂,thus causing to reduce defects,facilitate the spreading of perovskite solution on the surface of ETLs,promote the uniform growth of perovskite layer,and facilitate the collection and transmission of electrons.The PSCs prepared by SnO₂ETLs with hydrothermally treatment at 100℃for3 h showed the best performance,the highest PCE of cell was 15.48%,the open-circuit voltage(V_oc)was 1.09 V,the short-circuit current density(J_sc)was 19.32 m A/cm~2and fill factor（Fill Factor,FF）was 73.18%,respectively.（2）OTS was used as an interfacial modification layer between SnO₂ETLs/perovskite layers,and the effects on the performances of SnO₂films,perovskite films and PSCs were studied.The concentrations of OTS in hexane were 0.05 mol/L,0.1mol/L,0.25 mol/L,0.5 mol/L,respectively.Analysing by SEM and EDS tests,SnO₂films were covered by OTS well,OTS can fill the surface pores and depressions,make the film more flat and dense,and block the direct contact between the perovskite layer and the FTO,thus causing leakage current.At the same time,Cl^-in OTS can diffuse in the perovskite solution,it was propitious to enhance the crystallinity of perovskite,increase the grain size of perovskite,enhance the absorption of light by the perovskite layer,and effectively enhance the charge extraction and transmission.The PSCs prepared based on the interfacial modification of OTS at a concentration of 0.1 mol/L possessed the highest PCE of 15.39%and the cell V_oc,J_sc,and FF was 1.08 V,19.21 m A/cm~2,and 73.78%,respectively,and the cell hysteresis coefficient HI was reduced from 0.087 to 0.021.（3）A one-step antisolvent method was used to prepare perovskite layers.Anisole,chlorobenzol,isopropanol,chlorobenzol and acetonitrile,chlorobenzol and isopropanol were used as antisolvent to perpare perovskite.The effects of different antisolvents on perovskite films and the photoelectric performance of PSCs were studied.SEM tests showed that the grain size and film thickness of the perovskite layers prepared by the antisolvent of anisole and mixed antisolvent of chlorobenzol and acetonitrile were increased compared to chlorobenzol,and XRD tests showed the best crystallinity of perovskite prepared by mixed antisolvent of chlorobenzol and acetonitrile,with enhanced film crystallinity,increased grain size,thus causing to reduce grain boundaries,and enhance light absorption by perovskite.Perovskite layers were prepared by a mixed antisolvent of chlorobenzol and acetonitrile and assembled into PSCs,cell showed the best photovoltaic performance with the cell PCE of 14.99%,V_ocof 1.09 V,J_scof 19.24m A/cm~2and FF of 71.15%.