Optimization Of SnO₂ Electron Transport Layer In Perovskite Solar Cells

In the past decade,the development of perovskite solar cells（PSCs）has made remarkable progress.As a research hotspot in the photovoltaic field,power conversion efficiency of PSCs has risen to 25.7%.The electron transport layers greatly affect the performance of PSCs.SnO₂ is the most widely used ETLs in perovskite solar cells.SnO₂ electron transport layers are favored for their excellent carrier transport performance,but there are still some drawbacks during use,such as the presence of nanoparticles in the precursor solution of SnO₂,interfacial defects at the interface between the SnO₂ electron transport layer and the perovskite layer,and the energy level distribution of SnO₂ in the whole device was not perfect.Here,through solvent engineering and interface modification strategies,using organic solvents acetonitrile and polyhydroxy compound sodium L-ascorbate to optimize the preparation of SnO₂electron transport layers and the upper buried interface,to explore the final effect on the photovoltaic performance of devices.The main focus of this paper and the conclusions obtained are as listed below:（1）The precursor solution of SnO₂ was prepared using acetonitrile partially instead of ultrapure water,and the process was optimized during the deposition process of the electron transport layer,that is,a brief vacuum treatment was applied to the SnO₂wet film to improve the morphology of the film.The test result showed that the addition of acetonitrile makes the distribution of SnO₂ colloid more uniform,effectively improving the film quality of the electron transport layer.After solvent engineering optimization,the transmission of the SnO₂ electron transport layer prepared in the ultraviolet visible band has been significantly improved.Moreover,the organic solvent significantly reduces the contact angle between the SnO₂ precursor solution and the FTO conductive glass,indicating that the wettability of the precursor solution on the substrate is greatly improved,which can simplify the traditional preparation process that using ultraviolet-ozone irradiation treatment of the FTO conductive glass in advance,undoubtedly greatly simplifying the preparation process of perovskite solar cells.Using the optimized SnO₂ electron transfer layers as substrates,perovskite device with a power conversion efficiency of 22.28%can be prepared,which was increased by 16%compared to that of the control sample.（2）Using an interface modification strategy,the surface of the SnO₂ electron transport layer was modified with 0.4 mg/m L sodium L-ascorbate aqueous solution,successfully passivating the electron transport layer film and improving its surface wettability,which made the morphology of the subsequently deposited perovskite photocatalytic active layer denser and uniform,and the perovskite crystal size also increased.By arranging the energy level distribution of each functional layers in the device,we found that the optimized electron transport layer had a more reasonable arrangement of E_VB（semiconductor valence band value）and E_CB（semiconductor conduction band value）.The photoelectric performance test showed that the conductivity of the optimized SnO₂ electron transport layer was significantly improved,which enabled the device to achieve a high short circuit current density of 24.44mA/cm²,and its power conversion efficiency was as high as 22.73%.