Research On Defect Passivation Of Perovskite Layer Containing Polycyano Groups And Its Effect On The Performance Of Solar Cell

Energy and environmental issues are stimulating the global exploration of new energy technologies.Solar energy has become the main force in new energy due to its unlimited reserves,widespread presence across the earth,and pollution-free and renewable advantages.As the leader of the third-generation solar cells,perovskite solar cells have a conversion efficiency that has risen from 3.8%in 2009 to 25.5%,showing great appeal in terms of high performance and high efficiency.However,compared with leading photovoltaic technology,perovskite solar cells are generally not efficient,and they exhibit poor environmental stability.This is mainly due to the shallow or deep defects in the formation of perovskite crystals during the preparation by the solution spin coating method,so it is very necessary to passivate the defects.Based on this,we study the passivation of the perovskite layer to improve the perovskite solar cells performance.In order to achieve high efficiency perovskite solar cells,understanding both the crystal structure and the opto-electronic properties of perovskite layers are of importance.First,we studied the liquid-phase one-step and liquid-phase two-step processes commonly used in the preparation of perovskite.With similar perovskite composition and a band gap of 1.58 e V,the perovskite layer obtained by the liquid-phase one-step method has a better crystal structure and fewer defect states.This results in a higher open circuit voltage V_OC and fill factor FF,thus showing a higher conversion efficiency PCE.Based on this,we will study the passivation of perovskite solar cells based on the liquid phase one-step method in the following research.Next,we studied the use of 4-hydroxyphthalonitrile(4HPN)and4-aminophthalonitrile(4APN)for the passivation of perovskites containing electron-donating polycyanomolecules.The hydroxyl and amino groups in 4HPN and4APN are expected to interact with negatively charged defects in perovskites,while cyano groups interact with positively charged defects in perovskites.At the same time,4HPN and 4APN can play a cross-linking role,which can effectively improve the perovskite crystal structure.Adding 4HPN to the perovskite layer resulted in an improved perovskite crystal structure and improved perovskite solar cells performance,which increased the efficiency from 20.8%of the reference to 21.6%.However,the addition of 4APN did not play the desired role,and only played a minor role.This may be due to the strong electronegativity of hydroxyl oxygen on 4HPN,which increases its electron cloud density,which is not found on amino groups.Multiple functional groups with rich-electrons enable 4HPN to have more sites for binding with uncoordinated Pb²⁺,making 4HPN more passivating.Based on the passivation of perovskite molecules containing electron-donating groups,we further proposed the use of electron-withdrawing group-containing polycyanomolecules to interact with perovskites,using a simple passivation molecule4-nitro Phthalonitrile(4NPN),its ?-? acceptor nitro group(-NO₂)and cyano group(-CN),can passivate charged defects in perovskites.Different from the above molecules forming cross-linking with perovskite,4NPN will mainly act as a Lewis base to directly interact with the positively charged defects in the perovskite.Adding electron-deficient 4NPN to the perovskite layer of the perovskite solar cell can not only increase the open circuit voltage V_OC and fill factor FF,increase the efficiency to more than 22%,and improve its environmental stability.These improvements are due to the strong polarized nitro/cyano group for effective passivation of perovskite film defects.In addition,the electron-deficient 4NPN can slightly adjust the energy level of the perovskite,thereby promoting more effective hole transfer.