Mechanisms of exceptional grain growth and stability in formamidinium lead triiodide thin films for perovskite solar cells
Mechanisms of exceptional grain growth and stability in formamidinium lead triiodide thin films for perovskite solar cells
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DOI：
10.1016/j.actamat.2020.03.036
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发表时间：
2020-07
期刊：
影响因子：
9.4
通讯作者：
Srinivas K. Yadavalli;Zhenghong Dai;Mingyu Hu;Qingshun Dong;Wenhao Li;Yuanyuan Zhou;R. Zia;N. Padtur
中科院分区：
文献类型：
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作者：
Srinivas K. Yadavalli;Zhenghong Dai;Mingyu Hu;Qingshun Dong;Wenhao Li;Yuanyuan Zhou;R. Zia;N. Padtur
纯甲脒型三碘化铅（α-FAPbI3）有机-无机卤化物钙钛矿（OIHP）半导体作为光吸收剂在新型薄膜钙钛矿太阳能电池（PSCs）技术中具有重要的应用前景。这主要是因为其优越的热稳定性，更合适的带隙，和组成简单。然而，光活性非钙钛矿δ- fapbi3多晶（“黄色”相）的存在是α- fapbi3基PSCs发展道路上的主要障碍。此外，人们普遍认为，OIHP薄膜的细粒度性质不利于环境稳定性和由此产生的psc的性能。在此背景下，我们利用FAPbI3的多态性，利用溶剂-蒸汽辅助δ-to-α相变，在0.3 μm厚度的FAPbI3薄膜中诱导出异常的晶粒粗化（高达50倍），导致前所未有的平均晶粒尺寸高达~9 μm。通过对时间、温度、初始晶粒尺寸和溶剂极性指数（PI）的影响进行系统研究，阐明了其机理。超粗晶α- fapbi3薄膜的环境稳定性明显优于中晶α- fapbi3薄膜，这是基于晶界密度参数的解释。采用超粗晶α- fapbi3薄膜制备的PSCs提高了光伏（PV）性能，但效果不大。这是由于低估了与光载流子动力学相关的有效晶粒尺寸。
Pure formamidinium lead triiodide (α-FAPbI3) organic-inorganic halide perovskite (OIHP) semiconductor is very attractive for use as light absorber in the new thin-film perovskite solar cells (PSCs) technology. This is primarily because of its superior thermal stability, more suitable bandgap, and compositional simplicity. However, the existence of the photo-inactive non-perovskite δ-FAPbI3polymorph (‘yellow’ phase) is a major hurdle in the path towards the development of α-FAPbI3-based PSCs. Also, there is general consensus that the fine-grained nature of OIHP thin films is detrimental to the environmental stability and performance of the resulting PSCs. In this context, here we take advantage of the polymorphism in FAPbI3, and use solvent-vapor-assisted δ-to-α phase transformation to induce exceptional grain coarsening (up to 50-fold) in 0.3-μm thickness FAPbI3thin films, resulting in an unprecedented average grain size of up to ~9 μm. The underlying mechanisms are elucidated based on the results from a combination of some key experiments, which involve studying systematically the effects of time, temperature, initial grain size, and solvent polarity index (PI). The ultra-coarse-grained α-FAPbI3thin films show dramatically improved environmental stability over their medium-grained counterparts, which is explained based on grain-boundary density arguments. PSCs made using the ultra-coarse-grained α-FAPbI3thin films have improved photovoltaic (PV) performance, but it is somewhat modest. This is attributed to the underestimation of the effective grain size relevant to photocarrier dynamics.