Study On The Modification Of Electron Transport Layer And Interface Modification Of Perovskite Solar Cells By Inorganic Salts

Since the emergence of perovskite solar cells（PSCs）in 2009,its photoelectric conversion efficiency（PCE）has rapidly increased from 3.8%to 25.7%,showing great application potential in the field of photovoltaics.SnO₂ has become an ideal electron transport layer（ETL）material for efficient and stable PSCs due to its high transmittance,good charge mobility and good chemical stability.However,there are inherent defect states on the surface of SnO₂ films,such as oxygen vacancies and hydroxyl groups.These defects capture electrons at the SnO₂/perovskite interface and form a barrier to hinder the transmission of photogenerated electrons,thus limiting the photovoltaic performance of PSCs.How to prepare SnO₂ films with excellent performance and construct a perfect SnO₂/perovskite interface is of great significance for further improving the photovoltaic performance of PSCs.In this paper,SnO₂ ETL was modified by inorganic salt Cu Cl₂,and SnO₂/perovskite interface was modified by inorganic salt Sb Cl₃ and（NH₄）₂S to reduce the defect state of SnO₂/perovskite interface and improve the transmission of photogenerated carriers,thereby improving the photoelectric performance of PSCs.The specific contents of the paper are as follows:（1）CuCl₂ was introduced to modify SnO₂ ETL to reduce its surface defect states.The experimental results show that the introduction of Cu Cl₂ in the colloidal dispersion of SnO₂ can oxidize Sn²⁺on the surface of SnO₂ nanocrystals to Sn⁴⁺,reduce the oxygen vacancies on the surface of SnO₂ thin film,improve its conductivity as ETL,and obtain a good energy level matching with the perovskite layer.In addition,Cu Cl₂ modified SnO₂ETL can further improve the crystal quality of perovskite films.Compared with the control device（18.15%）,the PSCs prepared by Cu Cl₂ modified SnO₂ ETL showed higher PCE（20.31%）and higher environmental stability.At the same time,Cu（NO₃）₂·3H₂O was used to modify SnO₂ ETL,and the effect was similar to that of Cu Cl₂,which fully indicated that Cu²⁺played a leading role in the modification mechanism of SnO₂ ETL.（2）SbCl₃ was introduced at the SnO₂/perovskite interface for modification.The experimental results show that,the introduction of Sb Cl₃ reduces the charge traps on the surface of SnO₂,thereby inhibiting the charge recombination at the SnO₂/perovskite interface.In addition,Cl^-ions diffuse into the perovskite layer and form Cl-Pb bonds with the uncoordinated Pb²⁺ions in the perovskite,thereby passivating Pb defects.Finally,the PSCs device modified with Sb Cl₃ obtained 20.69%PCE.After 16 days of storage in air（relative humidity of 35%）,the PSCs device efficiency was 87.9%of the initial value,showing good environmental stability.（3）（NH₄）₂S was introduced at the SnO₂/perovskite interface for modification.The experimental results show that NH₄⁺ions reduce the density of hydroxyl defect states on the surface of SnO₂ films,thereby enhancing the hydrophobicity of the interface and reducing the nucleation sites of perovskite,which is beneficial to increase the perovskite grains.At the same time,S^2-can not only fill the oxygen vacancies on the surface of SnO₂,but also interact with uncoordinated Pb²⁺to reduce Pb defects at the interface,thereby inhibiting charge recombination at the interface.After（NH₄）₂S modification,the open circuit voltage of the device increased from 1.07 V to 1.11 V,the photoelectric conversion efficiency reached 20.53%,and the long-term stability in air was improved.