Study On Stability Of Perovskite Photovotaic Devices

With the overuse of fossil fuels such as oil and natural gas,the whole world is facing serious problems such as energy shortage and environmental pollution.In this regard,countries have formulated carbon emission reduction,clean energy and other policies,and development and utilization of clean and renewable energy has become increasingly urgent.As a renewable and clean energy with abundant resource,low cost and environmental friendliness,solar energy can undoubtedly alleviate problems such as energy shortage and environmental degradation if it can be used reasonably,which is of great help to the sustainable development of the global economy.In recent years,countries around the world have paid more and more attention to and research on solar photovoltaic cells.Perovskite materials have attracted much attention in the new generation of solar photovoltaic cells due to their advantages of high light absorption coefficient,low exciton binding energy,high carrier mobility and carrier lifetime,and adjustable band gap and so on.At present,the highest photoelectric conversion efficiency of perovskite solar cells has reached 25.8%(certified 25.7%).As one of the perovskite materials,formamidine lead iodide FAPbI3 has better thermal stability and more ideal band gap than the more widely studied methylamine lead iodide MAPbI3,so FAPbI3 is more suitable for commercial perovskite solar cells application.However,due to the defects formed in the preparation of polycrystalline FAPbI3 perovskite thin films,as well as inherent phase instability of FAPbI3,these have hindered the long-term stability of FAPbI3 perovskite solar cells(FAPbI3 PSC)in the external natural environment,thus affecting commercial development and promotion of FAPbI3 PSC,making it impossible to further utilize solar energy resources to alleviate the global energy crisis.Additive engineering is one of the most commonly used methods to improve performance of perovskite solar cells.Adding additives can help control the crystallization and surface morphology of perovskite films,and passivate defects of films,thereby making device performance and stability of perovskite cells improved.In this paper,we used two different additive engineering to passivate FAPbI3 film defects and improve the film quality to improve the stability and optoelectronic performance of corresponding FAPbI3 devices.The specific research contents are as follows:(1)The formamidine lead iodide FAPbI3 film was prepared by a two-step spin coating method by adding dimethyl itaconate to the PbI2 precursor solution.The uncoordinated Pb2+dangling bond in FAPbI3 was passivated by dimethyl itaconate,so as to reduce the non-radiative recombination of carriers in the film.The device photoelectric conversion efficiency(PCE)of FAPbI3 increased from 16.63%to 17.37%after adding the optimal concentration(5%)of dimethyl itaconate.Aging test about stability were carried out in a constant humidity(6%)air atmosphere glove box.After 200 hours,the normalized efficiency of the FAPbI3 device without the addition of dimethyl itaconate dropped to about 96%of the initial efficiency,while the normalized efficiency of the FAPbI3 device with the optimal dimethyl itaconate addition concentration dropped to about 97%of the initial efficiency,it proved that the long-term stability was improved.(2)Formamidine formate(FAHCOO)was added to PbI2 precursor to prepare FAPbI3 thin films by a two-step spin-coating method.The I-vacancy defect in FAPbI3 was passivated by HCOO-ions in FAHCOO,thereby reducing the non-radiative recombination and ionic migration in the films.In addition,the addition of FAHCOO could provide FAPbI3 template for the second reaction and induce the growth of specific crystal planes,thus improving the quality of perovskite thin films.After optimization,it was found that the device efficiency of FAPbI3 increased from 16.69%to 19.04%when the addition amount of formamidine formate was 5%.Aging test about stability was carried out in a constant humidity(6%)air atmosphere glove box.After 200hours,the normalized efficiency of the FAPbI3 device without the addition of formamidine formate dropped to about 95.6%of the initial efficiency,while the normalized efficiency of the FAPbI3 device with the optimal concentration of formamidine fonnate addition dropped to about 98%of the initial efficiency,which proved that formamidine formate could improve the stability of FAPbI3 device in air environment.Then we studied the effect of formamidate formate on the operational stability of FAPbI3 solar cell through a maximum power point tracking test under standard sunlight AM1.5G.Among them,the FAPbI3 device with 5%formamidine formate maintains 100%of the initial efficiency after the maximum power point tracking test under 4100 s illumination,while the FAPbI3 control device without formamidate formate decreased to about 94%of the initial efficiency.It showed that formamidine formate had a good effect on improving operational stability of perovskite photovoltaic devices.