Vasileiadou Eugenia S, Wang Bin, Spanopoulos Ioannis, Hadar Ido, Navrotsky Alexandra, Kanatzidis Mercouri G
Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.
Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California Davis, Davis, California 95616, United States.
J Am Chem Soc. 2021 Feb 17;143(6):2523-2536. doi: 10.1021/jacs.0c11328. Epub 2021 Feb 3.
Two-dimensional (2D) hybrid organic-inorganic halide perovskites are a preeminent class of low-cost semiconductors whose inherent structural tunability and attractive photophysical properties have led to the successful fabrication of solar cells with high power conversion efficiencies. Despite the observed superior stability of 2D lead iodide perovskites over their 3D parent structures, an understanding of their thermochemical profile is missing. Herein, the calorimetric studies reveal that the Ruddlesden-Popper (RP) series, incorporating the monovalent-monoammonium spacer cations of pentylammonium (PA) and hexylammonium (HA): (PA)(MA)PbI ( = 2-6) and (HA)(MA)PbI ( = 2-4) have a negative enthalpy of formation, relative to their binary iodides. In contrast, the enthalpy of formation for the Dion-Jacobson (DJ) series, incorporating the divalent and cyclic diammonium cations of 3- and 4-(aminomethyl)piperidinium (3AMP and 4AMP respectively): (3AMP)(MA)PbI ( = 2-5) and (4AMP)(MA)PbI ( = 2-4) have a positive enthalpy of formation. In addition, for the (PA)(MA)PbI family of materials, we report the phase-pure synthesis and single crystal structure of the next member of the series (PA)(MA)PbI ( = 6), and its optical properties, marking this the second = 6, bulk member published to date. Particularly, (PA)(MA)PbI ( = 6) has negative enthalpy of formation as well. Additionally, the analysis of the structural parameters and optical properties between the examined RP and DJ series offers guiding principles for the targeted design and synthesis of 2D perovskites for efficient solar cell fabrication. Although the distortions of the Pb-I-Pb equatorial angles are larger in the DJ series, the significantly smaller I···I interlayer distances lead to overall smaller band gap values, in comparison with the RP series. Our film stability studies on the RP and DJ perovskites series reveal consistent observations with the thermochemical findings, pointing out to the lower extrinsic stability of the DJ materials in ambient air.
二维（2D）有机-无机卤化物杂化钙钛矿是一类卓越的低成本半导体，其固有的结构可调性和吸引人的光物理性质已促成了具有高功率转换效率的太阳能电池的成功制备。尽管观察到二维碘化铅钙钛矿比其三维母体结构具有更高的稳定性，但对其热化学概况仍缺乏了解。在此，量热研究表明，包含戊基铵（PA）和己基铵（HA）等单价单铵间隔阳离子的Ruddlesden-Popper（RP）系列：(PA)ₙ(MA)PbI₃ₙ₊₁（n = 2 - 6）和(HA)ₙ(MA)PbI₃ₙ₊₁（n = 2 - 4）相对于其二元碘化物具有负的生成焓。相比之下，包含3-和4-（氨甲基）哌啶鎓（分别为3AMP和4AMP）等二价和环状二铵阳离子的Dion-Jacobson（DJ）系列：(3AMP)ₙ(MA)PbI₃ₙ₊₁（n = 2 - 5）和(4AMP)ₙ(MA)PbI₃ₙ₊₁（n = 2 - 4）具有正的生成焓。此外，对于(PA)ₙ(MA)PbI系列材料，我们报道了该系列下一个成员(PA)₆(MA)PbI₁₉的纯相合成、单晶结构及其光学性质，这是迄今为止报道的第二个n = 6的体相成员。特别地，(PA)₆(MA)PbI₁₉也具有负的生成焓。此外，对所研究的RP和DJ系列之间的结构参数和光学性质的分析为高效太阳能电池制备的二维钙钛矿的定向设计和合成提供了指导原则。尽管DJ系列中Pb-I-Pb赤道角的畸变较大，但与RP系列相比，明显更小的I···I层间距离导致整体带隙值更小。我们对RP和DJ钙钛矿系列的薄膜稳定性研究揭示了与热化学结果一致的观察结果，指出DJ材料在环境空气中的外在稳定性较低。
