The Research On The Photostability Of Perovskite Solar Cells

In recent years,the rapid advances of organic–inorganic hybrid perovskite semiconductors have enabled the significant developments in photovoltaic cells?PSCs?.However,the poor stability of the device fails by far the market requirements,becoming one of the major constraints to the development of the PSCs.Among all the factors which leads to the unstability of the PSCs,light is inevitable.In addition,the researches on the light induced changes in PSCs started late.There are lots of conflicting reports to date,not only the proposed mechanism but also the observed phenomenon.So far,there are few methods to improve the photostability of solar cells.This thesis focuses on the photostability of the perovskite solar cells and carries out the following research work:?1?CH₃NH₃PbI₃ films have been prepared by a two-step spin-coating method,and the influence of annealing temperature on the purity,surface morphology,grain size and charge transport characteristics of the CH₃NH₃PbI₃ film has been investigated.It was found that the optimal annealing temperature is 90?.At this annealing temperature,the property of CH₃NH₃Pb I₃ film is best,and the power conversion efficiency?PCE?of the device is highest.?2?The light induced changes in PSCs has been systematically studied based on the changes of the conductivity,structure,composition and surface morphology of the absorbed layer.It was found that as the extension of illumination time,the PCE of PSCs increased first,and then declined sharply.The buried mechanism was put forward,which is that when the device is exposed in light,the junction can form photovoltage from hole transport layer?HTL?to electron transport layer?ETL?.Under the action of electric field generated by light,the positive ions/vacancies in CH₃NH₃PbI₃ can be driven toward ETL side.At the same time,the negative ions/vacancies are driven toward HTL side.The accumulated chargescan increase the band-bending and the built-in voltage is increased as well.So,in the first few minutes,performance of the device is improved.But if the device is exposed in light for a longer time,CH₃NH₃PbI₃ will disintegrate into CH₃NH₃I and Pb I₂,much slit was appeared on the surface of absorbed layer,therefore performance of the device will decrease?3?According to the mechanism of light induced changes in PSCs,the photostability of PSCs was improved by improving the quality of absorbed layer,in which FA⁺was added into MAPb I₃.?4?In order to further improve the photostability of the PSCs,we focused on the hole transport layer.The NiO_x film obtained by magnetron sputtering was acted as the hole transport layer of the PSCs.Based on the characterizations of NiO_x prepared by different rf power,we found that 60W is optimal.By using NiO_x instead of Spiro-OMeTAD as the hole transport layer,and Zn O or PCBM as electron transport layer of the PSCs,the photostability of the PSCs was improved.