The Optoelectronic Properties Of Carboxyl-passivated Perovskite Solar Cell

Today,the use of clean energies is extremely important to address the increasingly serious environmental problems,and solar energy is the most important clean energy.Photovoltaic perovskite materials have the advantages of simple preparation,low cost,as well as excellent photoelectric properties（such as high light absorption coefficient and long carrier diffusion length）.It was once rated as one of the top ten scientific discoveries in 2012,and has attracted the intensive attention of researchers.At present,the performance and stability of perovskite solar cells are mainly affected by the defects,and passivation engineering is an important way to control the density of defect states,leading to the improvement of efficiency and stability.This thesis focuses on the passivation of the perovskite active layer and regulates the growth of perovskite crystals,to obtain low defect state density perovskite films and improve the performance and stability of perovskite solar cells.The major results are as following:（1）In this paper,during the optimization process of perovskite solar cell,the influence of the polycarboxyl passivator on the perovskite film is studied.It was found that the defect state density of the perovskite decreased with the increase of the number of carboxyl groups,but when the defect state density was reduced to a certain extent,the performance improvement of the perovskite solar cells is slight.At the same time,this study also found that because of the many passivation sites,different passivation sites can interact with different perovskite octahedrons,which affects the carrier migration inside the perovskite and makes it pass through the multiple carboxyl sites.The short-circuit current density of the passivated device is reduced.In addition,the addition of carboxyl group passivation will also affect the crystallinity and morphology of the perovskite.（2）Trifluoromethylphenylacetic acid（TFPA）is introduced as the accelerant of Ostwaldripening to develop an in-situ crystal growth control（ICGC）strategy for high-quality thin films.With adding a proper amount of TFPA into the FAI/MAX（X is Br and Cl）precursor in the two-step method,the larger grain size and reduced defect density perovskite are achieved due to Ostwald ripening.The ICGC process makes the average particle size from 476 to 625nm.The defect density is reduced by a factor of 3.18.The high-quality thin film endows the powerconversionefficiencyofchampionperovskitesolarcell（Sn O₂/perovskite/spiro-OMe TAD）higher than 22.19%.Furthermore,TFPA is insoluble in the water and thus TFPA modified film is resistive to moisture.The device can be stored in an argon glove box for 2000 hours without efficiency change and when exposed to 65-75%relative humidity for more than 1500 hours it retains more than 85%of the initial PCE.