Sharma Romika, Zhang Qiannan, Nguyen Linh Lan, Salim Teddy, Lam Yeng Ming, Sum Tze Chien, Duchamp Martial
School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Technological University, Singapore 639798, Singapore.
School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore.
ACS Nanosci Au. 2023 Mar 28;3(3):230-240. doi: 10.1021/acsnanoscienceau.2c00065. eCollection 2023 Jun 21.
Organic-inorganic halide perovskites are interesting candidates for solar cell and optoelectronic applications owing to their advantageous properties such as a tunable band gap, low material cost, and high charge carrier mobilities. Despite making significant progress, concerns about material stability continue to impede the commercialization of perovskite-based technology. In this article, we investigate the impact of environmental parameters on the alteration of structural properties of MAPbI (CHNHPbI) thin films using microscopy techniques. These characterizations are performed on MAPbI thin films exposed to air, nitrogen, and vacuum environments, the latter being possible by using dedicated air-free transfer setups, after their fabrication into a nitrogen-filled glovebox. We observed that even less than 3 min of air exposure increases the sensitivity to electron beam deterioration and modifies the structural transformation pathway as compared to MAPbI thin films which are not exposed to air. Similarly, the time evolution of the optical responses and the defect formation of both air-exposed and non-air-exposed MAPbI thin films are measured by time-resolved photoluminescence. The formation of defects in the air-exposed MAPbI thin films is first observed by optical techniques at longer timescales, while structural modifications are observed by transmission electron microscopy (TEM) measurements and supported by X-ray photoelectron spectroscopy (XPS) measurements. Based on the complementarity of TEM, XPS, and time-resolved optical measurements, we propose two different degradation mechanism pathways for air-exposed and non-air-exposed MAPbI thin films. We find that when exposed to air, the crystalline structure of MAPbI shows gradual evolution from its initial tetragonal MAPbI structure to PbI through three different stages. No significant structural changes over time from the initial structure are observed for the MAPbI thin films which are not exposed to air.
有机-无机卤化物钙钛矿因其具有诸如可调节的带隙、低材料成本和高载流子迁移率等有利特性，成为太阳能电池和光电子应用中令人感兴趣的候选材料。尽管取得了重大进展，但对材料稳定性的担忧仍然阻碍着基于钙钛矿的技术的商业化。在本文中，我们使用显微镜技术研究了环境参数对MAPbI（CH₃NH₃PbI₃）薄膜结构性质变化的影响。这些表征是在制成后转移到充满氮气的手套箱中的MAPbI薄膜上进行的，这些薄膜暴露于空气、氮气和真空环境中，后者通过使用专用的无空气转移装置得以实现。我们观察到，与未暴露于空气的MAPbI薄膜相比，即使暴露于空气中不到3分钟也会增加对电子束劣化的敏感性，并改变结构转变途径。同样，通过时间分辨光致发光测量了暴露于空气和未暴露于空气的MAPbI薄膜的光学响应的时间演变和缺陷形成。在较长时间尺度上，首先通过光学技术观察到暴露于空气中的MAPbI薄膜中缺陷的形成，而通过透射电子显微镜（TEM）测量观察到结构变化，并得到X射线光电子能谱（XPS）测量的支持。基于TEM、XPS和时间分辨光学测量的互补性，我们提出了暴露于空气和未暴露于空气的MAPbI薄膜的两种不同降解机制途径。我们发现，当暴露于空气中时，MAPbI的晶体结构通过三个不同阶段从其初始的四方MAPbI结构逐渐演变为PbI₂。未暴露于空气的MAPbI薄膜未观察到随时间从初始结构发生明显的结构变化。
