Synthesis Of Bismuth Compound And Their Application In Perovskite Solar Cells

Perovskite solar cells?PVSCs?,as the hottest third-generation solar cells in recent years,have the advantages of high power conversion efficiency?PCE?,and solution processed preparation.The outstanding performance of perovskite solar cells mainly comes from the excellent photoelectric properties of the perovskite light-absorbing layer,which mainly include its adjustable composition and band gap,high carrier mobility,long carrier diffusion distance,and high extinction coefficient.In just ten years of development,perovskite solar cells have entered the ranks of solar cells with high power conversion efficiency.But to achieve its commercial application,it must improve the device's power conversion efficiency while improving its stability.SnO₂ is a commonly used electron transport layer in perovskite solar cells.It has excellent optoelectronic properties such as high light transmission and high electrical conductivity.In addition,SnO₂ can be processed through low-temperature solution preparation method.It is considered to be ideal electron transport layer material for flexible perovskite solar cell devices.However,there are some problems in the preparation of SnO₂electron transport layer through low temperature solution preparation,mainly including the existence of a large number of oxygen vacancies and pinholes and cracks on the SnO₂ surface,which will cause charge recombination and leakage current.Bismuth compounds?Bi₂O₂S,Bi₂O₂Se,Bi₂OS₂,etc.?are considered to have the advantages of ultra-high carrier mobility and suitable band gap etc.and thus are considered to have great application potential in the fields of optoelectronics,thermoelectricity,photocatalysis.This main contains of this thesis is to synthesize several bismuth-based compounds and apply them to regulate the SnO₂ electron transport layer and perovskite light absorption layer,thereby improving the power conversion efficiency and stability of perovskite solar cells.The specific content is as follows:?1?Pure Bi₂O₂S material was synthesized and successfully used to modify the SnO₂ electron transport layer.The modified SnO₂ electron transport layer exhibits reduced oxygen vacancies,which will contribute to reducing the oxygen vacancies related defect recombination and achieving better charge transport.The modified SnO₂ electron transport layer has improved morphology and reduced surface energy,which will be helpful to the upper perovskite crystal growth.The power conversion efficiency of the modified MAPb I₃ based perovskite solar cell device was increased from 14.61%to 17.13%,and the stability was also improved.Besides,this method is also applicable to?Cs FAMA?Pb?IBr?₃ based perovskite solar cells.The power conversion efficiency of the modified perovskite solar cell devices was increased from 18.10%to 20.14%.?2?Pure Bi₂O₂Se material was synthesized and firstly used as an electron transport layer in perovskite solar cell.The power conversion efficiency of the devices?9.12%?is increased by110%compared with that of devices without an electron transport layer?4.32%?.We further proposed the SnO₂/Bi₂O₂Se bilayer electron transport layer structure and made a series of tests.Photoelectric properties and surface morphology tests demonstrate that it has better light transmission,higher electrical conductivity,and even surface morphology.The perovskite film deposited on the SnO₂/Bi₂O₂Se bilayer electron transport layer exhibits larger perovskite crystal grains and better crystallinity.We further prepared perovskite solar cells and performed characterization tests.The power conversion efficiency of devices based on the SnO₂/Bi₂O₂Se bilayer electron transport layer?19.06%?is increased by 17%compared with that of devices based on SnO₂ electron transport layer?16.29%?.In addition,the stability of SnO₂/Bi₂O₂Se bilayer electron transport layer devices has also been greatly improved.?3?The Bi₂OS₂ material was synthesized and peeled into a two-dimensional nanosheet structure by liquid exfoliation methods.The effect of adding Bi₂OS₂ with different concentrations into the perovskite light-absorbing layer was fully studied.Additive Bi₂OS₂ can form a Pb-S bond with unbounded Pb²⁺in the perovskite thin film,while uncorporated lead ions mainly located at the grain boundaries of the perovskite thin film could capture transported electrons.Therefore,the formation of Pb-S bonds can effectively reduce non-radiative recombination.As a heterogeneous nucleation site,2D Bi₂OS₂ can reduce the nucleation barrier and assist the formation of large-grained perovskite films.However,excessive Bi₂OS₂ will produce too many nucleation sites,so that perovskite nuclei cannot have large growth space become large grains.The power conversion efficiency and stability of perovskite solar cells with an appropriate amount of Bi₂OS₂ additive are improved.Compared with non-additive PVSCs,PVSCs with0.02mg/m L Bi₂OS₂ additive have better perovskite crystallinity,larger grain size,and passivated defects.Thus,the power conversion efficiency?PCE?of the device was increased from 16.02%to 17.75%.