Alkali metal iodides and hydroiodic acid additives for phase-stability CsPbI&lt;sub&gt;3&lt;/sub&gt; films prepared at low temperature

Ya-Ting Yan,Bin-Qi Li,Jin-Hua Gu,Zhi-Li Zhu,Jing-Yan Zhang

doi:10.7498/aps.70.20201950

Abstract

Inorganic cesium lead triiodide (CsPbI3) perovskite films show great prospect due to their high thermal stability and ideal band gap energy. To be used as a photovoltaic absorber, the CsPbI3 must form the black phase (α-CsPbI3). To prepare high-quality CsPbI3 films with phase stability in air at low temperatures, alkali metal iodides and hydroiodic acid (HI) additives are added into precursor solution. The results show that the quality and the phase stability of CsPbI3 with alkali metal iodides and HI additives are obviously improved compared with those with only HI additive. The SEM images show that the CsPbI3 film with 2.5% KI additive becomes more compact than that without KI additive and has no visible pinholes. As the KI additive increases, pinholes start to appear. From the XRD, it can be seen that the crystallinity of perovskite is improved when KI additive increases to 5.0%, while it starts to decrease with KI additive further increasing. The PL intensity of the CsPbI3 film with 2.5% KI additive is higher than the others’, implying a relatively low non-radiative recombination loss and low defect state in that film. And the CsPbI3 film with 2.5% KI additive exhibits increased absorption in the visible region, which is beneficial to enhancing the efficiency of perovskite solar cells. Considering the SEM images, crystallinity, PL intensity and light absorption of perovskite, the optimized KI additive is 2.5% in our work. For the CsPbI3 film with NaI additive, the SEM images show that the films become more compact and have no visible pinholes when NaI additive is 5%. As the NaI additive increases, pinholes appear. The crystallinity of perovskite increases with NaI additive increasing. The PL intensity of the CsPbI3 film with 5% NaI additive is higher than the others’, implying lower defect states in films. And the CsPbI3 film with 5% NaI additive exhibits the improved absorption in the visible region. Considering the SEM images, crystallinity, PL intensity and light absorption of perovskite, the optimized NaI additive is 5%. Therefore, adding alkali metal iodides and HI is an effective method to further improve the stability and efficiency of CsPbI3 perovskite solar cells.

Highlights

SEM surface images of CsPbI3 perovskite films doped with different KI content: (a) x = 0%; (b) x = 2.5%; (c) x = 5.0%; (d) x = 7.5%; (e) x = 10.0%
图 2 不同 KI 掺杂浓度 CsPbI3 薄膜的 (a) XRD 图谱与 (b)(100) 衍射峰半高宽 Fig. 2. (a) (XRD) patterns of CsPbI3 perovskite films doped with different KI content and (b) full width of half maximum at (100) peak
From the XRD, it can be seen that the crystallinity of perovskite is improved when KI additive increases to 5.0%, while it starts to decrease with KI additive further increasing

Summary

Introduction

本文, 在前驱液中同时添加碱金属碘化物 (NaI, KI) 和 HI 制备 CsPbI3 钙钛矿薄膜. 图 1 比较了不同 KI 掺杂浓度 CsPbI3 薄膜的 SEM 图像, 从图中看出, 未掺杂的 CsPbI3 薄膜孔洞较多, 薄膜不致密, 而 2.5% KI 掺杂浓的 CsPbI3 薄膜致密度提高, 表面无明显孔洞. 图 3 为不同 KI 掺杂浓度 CsPbI3 薄膜的 PL 谱和吸收谱. 图 3(b) 为不同 KI 掺杂浓度 CsPbI3 薄膜的吸收谱, 从图中可以看出 KI 掺杂对 CsPbI3 薄膜的带隙影响不大, 其中 2.5% KI 掺杂和未掺杂样品的带隙几乎一致, 而高浓度 (5.0%, 7.5%, 10.0%) 掺杂后 CsPbI3 薄膜的带隙略微减小.

Results

Conclusion