Wu Bo, Ning Weihua, Xu Qiang, Manjappa Manukumara, Feng Minjun, Ye Senyun, Fu Jianhui, Lie Stener, Yin Tingting, Wang Feng, Goh Teck Wee, Harikesh Padinhare Cholakkal, Tay Yong Kang Eugene, Shen Ze Xiang, Huang Fuqiang, Singh Ranjan, Zhou Guofu, Gao Feng, Sum Tze Chien
Guangdong Provincial Key Laboratory of Optical Information Materials and Technology and Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, P. R. China.
Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore.
Sci Adv. 2021 Feb 17;7(8). doi: 10.1126/sciadv.abd3160. Print 2021 Feb.
Bismuth-based double perovskite CsAgBiBr is regarded as a potential candidate for low-toxicity, high-stability perovskite solar cells. However, its performance is far from satisfactory. Albeit being an indirect bandgap semiconductor, we observe bright emission with large bimolecular recombination coefficient (reaching 4.5 ± 0.1 × 10 cm s) and low charge carrier mobility (around 0.05 cm s V). Besides intermediate Fröhlich couplings present in both Pb-based perovskites and CsAgBiBr, we uncover evidence of strong deformation potential by acoustic phonons in the latter through transient reflection, time-resolved terahertz measurements, and density functional theory calculations. The Fröhlich and deformation potentials synergistically lead to ultrafast self-trapping of free carriers forming polarons highly localized on a few units of the lattice within a few picoseconds, which also breaks down the electronic band picture, leading to efficient radiative recombination. The strong self-trapping in CsAgBiBr could impose intrinsic limitations for its application in photovoltaics.
铋基双钙钛矿CsAgBiBr被视为低毒性、高稳定性钙钛矿太阳能电池的潜在候选材料。然而，其性能远不能令人满意。尽管它是一种间接带隙半导体，但我们观察到其具有明亮的发射光，双分子复合系数较大（达到4.5±0.1×10 cm s）且电荷载流子迁移率较低（约为0.05 cm s V）。除了铅基钙钛矿和CsAgBiBr中都存在的中间弗罗利希耦合外，我们通过瞬态反射、时间分辨太赫兹测量和密度泛函理论计算，发现了后者中声子产生的强形变势的证据。弗罗利希势和形变势协同作用，导致自由载流子在几皮秒内超快自陷形成高度局域在晶格几个单元上的极化子，这也打破了电子能带图像，导致高效的辐射复合。CsAgBiBr中强烈的自陷可能会对其在光伏领域的应用造成内在限制。
