Researches On The Defect Passivation Of Perovskite Films And Their Applications In Solar Cells

Energy is the basis for promoting the development of human society.However,traditional fossil resources including coal and oil have shortcomings such as non-renewable and high pollution,and they can no longer meet the energy needs of human future development.Solar energy has attracted more and more countries and regions’ attention due to it is a kind of renewable and non-polluting clean energy.Therefore,solar cells have achieved rapid development.In 2009,a low-cost and easily prepared perovskite solar cell was proposed by Japanese scientists.After more than ten years of development,the power conversion efficiency of the device has increased from the initial 3.8%to the current 25.7%.Studies have shown that the theoretical upper limit of perovskite solar cell is as high as 33%.Therefore,it is possible for perovskite solar cells to replace silicon-based solar cells.However,the perovskite films prepared by the common preparation process are polycrystalline films.There are lots of defects in the bulk,surface,and interface.The existence of these defects causes severe carrier recombination,which affects the performance of the device.In this dissertation,surface treatment and additive engineering are used to regulate the defects of perovskite surface and bulk,respectively These strategies not only improved the power conversion efficiency of the perovskite solar cells,but also enhanced the stability.The specific research contents are as follows:(1)After the reaction of the perovskite film prepared by the two-step sequential deposition method,a large amount of lead iodide(PbI2)will remain on the surface of the perovskite,resulting in poor surface morphology and a large number of defects on the surface of the perovskite.In order to solve this problem,this work post-treats threedimensional(3D)perovskite with dodecylammonium bromide.The dodecylammonium bromide reacts with PbI2 on the surface of 3D perovskite to form a layer of two-dimensional(2D)perovskite and it will form a heterojunction of 2D/3D perovskite.On the one hand,the amino groups in dodecylammonium bromide passivate the surface defects of perovskite.On the other hand,the constructed 2D/3D heterojunction enhances the built-in electric field of the device,promoting the transport and separation of carriers.The power conversion efficiency of the optimal device reaches 21.81%.The formed 2D perovskite via long-chain dodecylammonium bromide enhances the stability of the devices,retaining 64%of the initial performance after 1065 h aging test in ambient air.(2)Formamidinium lead triiodide(FAPbI3)perovskite has become the preferred material for light-absorbing layer of high-performance perovskite solar cells due to its suitable bandgap and good thermal stability.However,the yellow phase(δ-FAPbI3)always exists in the prepared FAPbI3 films due to the large potential barrier of δ-FAPbI3 to photoactive black phase(α-FAPbI3).In addition,the quality of perovskite films is poor with lots of defects.By using N-(2-aminoethyl)acetamide as an additive for the FAPbI3 perovskite,the reaction barrier for the conversion from δ-FAPbI3 to α-FAPbI3 is lowered,enabling the formation of high-quality FAPbI3 perovskite films without δ-FAPbI3.The existence of carbonyl and amino groups in N-(2-aminoethyl)acetamide not only affects the process of the phase-transformation of the perovskite films,but also passivates the defects in perovskite bulk and inhibits the non-radiative recombination of carriers in the film.The improved quality of the photoactive layer is beneficial to enhance performance of the devices.The optimal power conversion efficiency of the device is 20.45%,the corresponding opencircuit voltage is 1.12 V,the short-circuit current density is 24.93 mA/cm2,and the fill factor is 0.73.Meanwhile,the chemical bond formed between N-(2-aminoethyl)acetamide and perovskite improves the stability of the devices.The optimized device still maintains 69%of the initial performance after 37 days of storage in ambient air.Under the same conditions,the original device performance has dropped to 0%.