Modification And Mechanism Study Of SnO₂ Based Electron Transport Layer In Perovskite Solar Cell

Perovskite Solar Cells(PSCs)as a new kind of solar cells,characterized by highly energy conversion efficiency,simple preparation process and low cost.Since 2009,its energy conversion efficiency has risen from 3.8%to 25.2%,making it comparable to today’s crystalline silicon solar cells.Perovskite solar cells are composed of transparent conductive oxide,electron transport layer(ETL),perovskite absorption layer,hole transport layer(HTL)and backside electrode.In which,the electron transport layer can extracts the charge,transmits the charge and blocks the hole.So far,researchers have developed many kinds of electron transport layer materials,including TiO2,ZnO,SnO2,PCBM,C60,etc.Among them,SnO2 material is an inorganic wide-gap semiconductor with good chemical stability,light transmittance and excellent electron mobility(240 cm2(V*s)-1),and can be prepared at low temperature.It is the most commonly used electron transport layer material nowadays.However,SnO2 material also has many disadvantages,which affect the efficiency and stability of perovskite solar cells.(1)There exist oxygen vacancy defects on the surface of SnO2 films,which cause recombination at SnO2/Perovskite interface.(2)There is an energy mismatch between SnO2 and perovskite materials,which leads to energy loss and reduces the open circuit voltage of the device.(3)The surface roughness of SnO2 greatly reduces the wettability of perovskite solution and affects the crystallization of perovskite.Aiming at the surface/interface problem of SnO2,this paper proposes an interface modification method to improve the photovolatic performance of the PSCs,and then the effects of different preparation methods on the properties of perovskite films and devices are studied.1.Corresponding functional layers deposited on the transparent conductive oxide by solution spinning and magnetron sputtering coating method to assemble the regular planar perovskite solar cells.Because the preparation process of SnO2 film without high temperature sintering,there exist oxygen vacancy defect on the surface.Which will affect the carrier transport and cause carrier recombination on the surface,reducing the photovoltaic performance of perovskite devices.This section is the first time to prepare GQDs interface modification layer by ultrasonic spraying method.The-OH andCOOH on the surface of GQDs can bond with Sn4+to offset the oxygen vacancy,andNH2 on GQDs surface can passivate the defect of perovskite.This bridge structure can effectively promote the carrier transport at the SnO2/perovskite interface.Inhibiting the carrier recombination in the perovskite,and enhance the photovoltaic performance of devices.When the concentration of GQDs solution is 0.05 mg mL-1 and the spraying time is 120 s,the highest performance achieved,and the device efficiency increased from 13.61%to 16.54%.2.In this section,sulfamic acid materials(Aulfamic acid,Aminomethylsulfonic acid,2-aminoethanesulfonic acid,3-amino-1-propanesulfonic acid)selected to modify the SnO2/perovskite interface.Sulfamic acid materials have simple molecular structure,it is easy to study its effect on the interface.Through test and analysis,found that the sulfonic acid group could bond with Sn4+to fill the oxygen vacancy,and the amino group could passivate the defect of perovskite.At the same time,the sulfamic acid(SA)promoted perovskite crystallization.Moreover,the sulfamic acid modify layer improves the Fermi level of SnO2,which relieves energy mismatch between SnO2 and perovskite.When 0.5 mg mL-1 sulfamic acid solution was use to modify SnO2,the device efficiency increased from 18.22%to 20.41%.3.In this section,the two-step preparation process of perovskite solar cells explored,and a simple,efficient and repeatable preparation process of perovskite solar cells concluded,with a device efficiency of 21.41%.After that,Amphetamine hydroiodate(PPAI)used to passivate perovskite films.Through analysis of perovskite the film,found that the PPAI could form a new two-dimensional perovskite phase PPA2PbI4 with the residual PbI2 on the surface of perovskite films.When 20 mM PPAI solution was use to passivate perovskite film,a maximum photovoltaic efficiency of 22.57%achieved.