Additive Regulation Strategy Of Two-Dimensional Perovskite Crystal And Applications In Photovoltaic Devices

In the past decade,there has been unprecedented rapid development of perovskite solar cells（PSCs）,with the power conversion efficiency（PCE）of three-dimensional（3D）PSCs surpassing 25%.However,the intrinsic instability of 3D PSCs has hindered their commercialization.Two-dimensional（2D）PSCs have greater potential for commercialization due to their superior stability.However,the record PCE of 2D perovskite is still much lower than 3D counterpart,mainly due to the poor electron transport properties of the organic amine introduced in 2D perovskites,which impedes carrier transport and ultimately impair device performance.Therefore,regulating the crystallization process of 2D perovskite,optimizing crystal orientation,and preparing higher quality 2D perovskite films are the key factors to achieve more efficient 2D PSCs.In this research,the new additives are introduced into the 2D perovskite layer to regulate the crystal growth,optimize the crystal orientation,and improve the film quality,ultimately leading to more efficient and stable 2D PSCs.The concrete research contents are as follows:（1）In this work,the 4-hydroxypyridine（4-HP）molecule is selected as the additive of the 2D perovskite layer,and the crystallization rate is delayed through the interaction between pyridine and hydroxyl functional groups of the 4-HP molecule and the 2D perovskite,which effectively regulate the crystal growth process to produce higher quality 2D perovskite films.The introduction of 4-HP molecules not only reduces defects in 2D perovskite films,but also induces 2D perovskite crystals in the film to be more inclined to vertical orientation and suppresses the formation of small n-valued phases,which greatly promotes carrier transport.Ultimately,compare with the control device（11.46%）,the PCE of the 4-HP optimized device increased to 14.82%.Moreover,the quality improvement in the 2D perovskite films enhances the stability of the optimized device under light,heat,and moisture.（2）In this work,three kinds of tetraphenylphosphonium halides molecules（Ph₄PX,X=I,Br,Cl）are selected and introduced into the 2D perovskite precursor solution by simple doping method to regulate crystallization of the 2D perovskite.Ph₄PX molecules have a strong interaction with 2D perovskite,which can improve the crystallinity and vertical orientation of 2D perovskite film crystals,thus preparing higher quality 2D perovskite films.Among the three additives,Ph₄PCl has the optimal crystallization control effect due to the higher electronegativity of Cl^-with stronger bonding to Pb²⁺than Br^-and I^-.Finally,the prepared 2D PSCs are increased from 11.37%of the control device to12.91%（Ph₄PI）,13.09%（Ph₄PBr）and 13.90%（Ph₄PCl）,respectively.Additionally,the optimized device also exhibits higher humidity and thermal stability.（3）In this work,the triphenylphosphine oxide（TPPO）molecule is used as an additive in the 2D perovskite layer to optimize the growth process of 2D perovskite crystals and prepare higher quality2D PSCs.The Lewis basic P=O functional group in the TPPO molecule coordinatively binds to the Lewis acidic Pb²⁺in the 2D perovskite precursor,which can effectively regulate the crystallization growth process.TPPO molecules not only passivate defects,but also induce the phase distribution of large n-valued phases at the bottom of the film,which suppresses the non-radiative recombination of2D perovskite films and enhances carrier transport.Ultimately,the PCE of the prepared 2D PSCs devices increased from 11.40%to 13.82%,with good operational stability and low hysteresis effect.Moreover,the water/oxygen stability of the optimized device is also improved,maintaining about 80%of the initial efficiency after 600 h aging at 25°C and 60%relative humidity,while the control device retains only 25%of the initial efficiency under the same conditions.