Preparation And Optimization On Functional Layers Of Perovskite Solar Cells

Perovskite solar cells are considered to be one of the most important and potential developments in photovoltaic technology due to their excellent performance and rapid development.The superior performance of perovskite solar cells is due to their long carrier lifetime and diffusion length.Further optimization of carrier transfer and transport within the perovskite photovoltaic device can improve the performance of the perovskite solar cells effectively.This paper focuses on improving the carrier extraction and suppressing the carrier charge recombination of perovskite devices to achieve better efficiency by employ SnO₂ as electron transport material（ETM）and use additive for perovskite and Spiro-OMeTAD.The main research contents and results are as follows:（1）Compared with TiO₂,SnO₂ has the advantages of higher electron mobility,more suitable energy level structure and low preparation temperature,which is more excellent ETM.We prepared a uniform aqueous solution of SnO₂ nanocrystal at room temperature by adjust the hydrolysis process of SnCl₂ in aqueous solution with the aid of appropriate hydrochloric acid.And then we prepared the SnO₂ electron transport layer（ETL）on the surface of FTO by spin coating using the aqueous solution of SnO₂nanocrystals.By optimizing the number of spin coatings,we can improve the film quality of the obtained SnO₂ ETL,which has better coverage,flatness and carrier extraction efficiency.The optimization of film can accelerate electron injection and transportation process,reduce the electron-hole recombination and improve the photovoltaic performance of devices fabricated based on this.Finally,we obtained 19.3%photoelectric conversion efficiency under optimal preparation conditions.（2）We introduce zinc acetylacetonate as an additive into the perovskite precursor solution.The introduction of Zn can reduce the density of defect states in the perovskite crystal effectively.The coordination of acetylacetonate with PbI₂ can effectively affect crystallization process of perovskite with obtaining perovskite film composed of uniform dense perovskite grains.Excessive PbI₂ in the precursor is tend to distribute in the grain boundary with the exist of zinc acetylacetonate that can passivating the defect of grain boundary.From the characterization of XRD,PL,TRPL,etc.,we can see that the added film has better crystallinity and smaller defect density,which is beneficial to increase the carrier transport in the perovskite film and reduce recombination.Thanks to the dual action of Zn²⁺and acetylacetonate,the device performance has been significantly improved.Compared with the unadded device,the short-circuit current density and fill factor of device are significantly improved,and the device performance increase from 17.9%to 19.7%.（3）We introduced tris（2-cyanoethyl）borate into the spiro solution as an additive to promote the oxidation of Spiro-OMeTAD,We discussed its influence mechanism by UV-vis,CV,NMR,hole mobility and other tests.The results show that the addition of borate can effectively promote the oxidation of Spiro.The improvement of device performance is mainly due to the higher hole mobility of the Spiro film,rather than the change of the energy level structure.PL and TRPL tests show that the higher conductivity of Spiro improves the hole extraction process and inhibits carrier recombination at the interface between perovskite and Spiro.Finally,the performance of devices increases from 17.7%to 19.5%.