Study On New-type Highly Stable Perovskite Materials

Since 2009,perovskite solar cells have achieved extremely rapid development due to their superior performance.In just a few years,the certified power conversion efficiencies(PCEs)have exceeded 24%,and they have become the most widely studied new star in the photovoltaic field.As the core part of the perovskite solar cells,the light absorption layer plays an important role in the power conversion efficiency and stability of the devices.However,the instability of the perovskite materials in humidity,light,oxygen or high-temperature environment has greatly limited further development and practical application of perovskite solar cells.In recent years,two-dimensional(2D)/mixed dimensional(MD)perovskite materials have attracted much attention owing to their high humidity stability.However,the devices based on the 2D/MD perovskite materials show poor photovoltaic performances because of their wide band gaps and large exciton binding energy.Thus,it is necessary to design new-type highly efficient and stable 2D and MD perovskite materials.In view of the above research background,we mainly focused on three progressive aspects:the preparation of new-type 2D/MD perovskites,the research of effect factors for 2D/MD perovskite performance and the mechanism of improved stability for 2D/MD perovskites.In order to obtain highly efficient and stable perovskite solar cells,we have carried out a series of research works,as follows:(1)Preparation of new-type two-dimensional/three-dimensional(2D/3D)mixed perovskite materials based on ammonium iodide.Through simulation calculation,it is found that the introduction of small-size ammonium salt into 3D perovskite can avoid the structural damage of 3D perovskite and maintain the original superior photovoltaic performance.Firstly,we innovatively introduced small size NH4' into 3D perovskite based on mixed FA and MA to prepare 2D/3D perovskite materials based on ammonium iodide.Different from the blue shift of other 2D/MD perovskites made from large size ammonium salts,the UV-vis absorption peak positions of new-type 2D/3D mixed perovskites exhibited red shift,the absorption intensities significantly increased and the band gaps decreased.Hence,they are more suitable to be used as the optical absorption layer.Consequently,the device based on this material achieved a high PCE of 18.25%,and the photovoltaic performance is comparable to that of conventional 3D perovskite solar cells.In addition,the devices displayed ultra-high humidity and light stability.(2)Preparation of highly efficient and stable MD perovskite solar cells based on ethanolamine.To improve the PCE and the stability of perovskite solar cells at the same time,we innovatively designed new-type MD perovskite materials by introducing ethanolamine iodide that contains hydroxyl into the 3D perovskite.The results showed that the MD perovskite devices with 3%ethanolamine iodide exhibited excellent photovoltaic performance,the PCE significantly increased to 18.79%.Meanwhile,the MD perovskite devices showed superior humidity,thermal and UV stability.(3)Effect of different ammonium salts on the properties of quasi-2D perovskites.In the aspect of exploring the factors that affect the properties of the 2D/MD perovskites,the effects of different ammonium salts on the properties of 2D perovskite were investigated firstly.Through a series of comparison,we finally adopted the most typical benzylamine,dimethylamine,1,3-propanediamine and 1,4-butanediamine to prepare four kinds of quasi-2D perovskite materials.As a result,we not only obtained quasi-2D perovskite solar cells based on benzylamine with high PCE of 17.40%and high humidity stability,but also found that the humidity stability of the quasi-2D perovskite materials depends on the hydrophobicity of the introduced ammonium salts.(4)Effect of different 2D constituent ratios and varisized ammonium salts on the performance of 2D perovskites.A series of 2D perovskite materials were prepared by adjusting the constituent ratios,n=3,5,7,9 and 11,and introducing varisized ammonium salts made from ethylamine,propylamine and butylamine.The results showed that there is a balanced relationship between the PCE and the humidity stability of 2D perovskites.It was concluded that the 2D perovskite solar cells based on the larger n and the smaller-size ammonium salt displayed higher PCE and lower humidity stability.When n is smaller and the size of ammonium salt is larger,the 2D perovskite solar cells exhibited lower PCE but higher humidity stability.(5)Mechanism study of the high humidity stability of MD perovskite based on NH4+.After obtaining highly efficient and stable MD perovskite materials,the mechanism of improving the stability of 2D perovskites was further studied.By analyzing the aging performance changes of MD perovskite based on ammonium iodide under different humidity,the mechanism of the high stability of MD perovskite was proposed and verified.It mainly showed three processes:Firstly,the cations exchange process of FA+ and NH4+;Then,the hydrated intermediate phase NH4PbX3*(H2O)2(X=I or Br)and 2D protective layers were formed that can avoid the decomposition of 3D perovskite;Meanwhile,the yellow FA phase was transformed into black FA phase under continuous illumination,which can remain the PCE of MD perovskite devices.The above research contents and results enable us to more clearly understand the properties of 2D/MD perovskite materials,which is conducive to the design of more efficient and stable perovskite materials.They also make us stride forward to realize the preparation of highly efficient and stable of perovskite solar cells,and lay a solid foundation for the practical application of perovskite solar cells.