Trap States in Lead Iodide Perovskites
Trap States in Lead Iodide Perovskites
复制标题
DOI：
10.1021/ja512833n
复制
发表时间：
2015-02-11
影响因子：
15
通讯作者：
Zhu, X. -Y.
中科院分区：
文献类型：
--
作者：
Wu, Xiaoxi;Trinh, M. Tuan;Zhu, X. -Y.
最近发现的基于碘化铅钙钛矿的高效太阳能电池导致了对理解这些材料中光载流子生成的研究活动激增，但对可能对太阳能电池性能有害的陷阱状态知之甚少。在这里，我们提供的三维（3D）CH 3 NH3 PbI 3钙钛矿薄膜的表面上的空穴陷阱和激子陷阱在这些材料中的光学间隙以下的直接证据。激子陷阱具有弱的光学跃迁强度，可以从上述带隙激发的弛豫中填充，并且随着维度从3D CH 3 NH3 PbI 3减小到二维（2D）（C4 H9 NH3 I）（2）（CH 3 NH3 I）（n-1）（PbI 2）（n）（n = 1，2，3）钙钛矿，并且在2D族中，随着n从3减小到1，激子陷阱变得更加显著。我们还表明，在氯化物的存在下生长的CH 3 NH3 PbI 3钙钛矿薄膜中的激子陷阱的密度比在没有氯化物的情况下生长的激子陷阱的密度低至少一个数量级，从而解释了一个广为人知的神秘的更好的太阳能电池性能的前者。陷阱状态可能是由电子声子耦合引起的，并且在钙钛矿晶体结构最容易变形的表面/界面处增强。
Recent discoveries of highly efficient solar cells based on lead iodide perovskites have led to a surge in research activity on understanding photo carrier generation in these materials, but little is known about trap states that may be detrimental to solar cell performance. Here we provide direct evidence for hole traps on the surfaces of three-dimensional (3D) CH3NH3PbI3 perovskite thin films and excitonic traps below the optical gaps in these materials. The excitonic traps possess weak optical transition strengths, can be populated from the relaxation of above gap excitations, and become more significant as dimensionality decreases from 3D CH3NH3PbI3 to two-dimensional (2D) (C4H9NH3I)(2)(CH3NH3I)(n-1)(PbI2)(n) (n = 1, 2, 3) perovskites and, within the 2D family, as n decreases from 3 to 1. We also show that the density of excitonic traps in CH3NH3PbI3 perovskite thin films grown in the presence of chloride is at least one-order of magnitude lower than that grown in the absence of chloride, thus explaining a widely known mystery on the much better solar cell performance of the former. The trap states are likely caused by electronphonon coupling and are enhanced at surfaces/interfaces where the perovskite crystal structure is most susceptible to deformation.