Center for Nanophotonics, AMOLF, Science Park 104, 1098, XG, Amsterdam, The Netherlands.
Department of Nanoengineering, University of California San Diego, CA, 92093, USA.
Adv Mater. 2018 Dec;30(52):e1804792. doi: 10.1002/adma.201804792. Epub 2018 Oct 26.
Grain boundaries play a key role in the performance of thin-film optoelectronic devices and yet their effect in halide perovskite materials is still not understood. The biggest factor limiting progress is the inability to identify grain boundaries. Noncrystallographic techniques can misidentify grain boundaries, leading to conflicting literature reports about their influence; however, the gold standard - electron backscatter diffraction (EBSD) - destroys halide perovskite thin films. Here, this problem is solved by using a solid-state EBSD detector with 6000 times higher sensitivity than the traditional phosphor screen and camera. Correlating true grain size with photoluminescence lifetime, carrier diffusion length, and mobility shows that grain boundaries are not benign but have a recombination velocity of 1670 cm s , comparable to that of crystalline silicon. Amorphous grain boundaries are also observed that give rise to locally brighter photoluminescence intensity and longer lifetimes. This anomalous grain boundary character offers a possible explanation for the mysteriously long lifetime and record efficiency achieved in small grain halide perovskite thin films. It also suggests a new approach for passivating grain boundaries, independent of surface passivation, to lead to even better performance in optoelectronic devices.
晶界在薄膜光电设备的性能中起着关键作用，但它们在卤化物钙钛矿材料中的作用仍未被理解。限制进展的最大因素是无法识别晶界。非晶态技术可能会错误识别晶界，导致关于它们影响的文献报告相互矛盾；然而，金标准 - 电子背散射衍射 (EBSD) - 会破坏卤化物钙钛矿薄膜。在这里，通过使用固态 EBSD 探测器解决了这个问题，该探测器的灵敏度比传统磷光屏和相机高 6000 倍。将真实晶粒尺寸与光致发光寿命、载流子扩散长度和迁移率相关联表明，晶界并非良性的，而是具有 1670 cm s 的复合速度，与晶体硅相当。还观察到非晶态晶界，导致局部光致发光强度增加和寿命延长。这种异常的晶界特征为在小晶粒卤化物钙钛矿薄膜中实现神秘的长寿命和创纪录的效率提供了可能的解释。它还为钝化晶界提供了一种新方法，与表面钝化无关，从而在光电设备中实现更好的性能。
