Li Junze, Ma Jiaqi, Cheng Xue, Liu Zeyi, Chen Yingying, Li Dehui
School of Optical and Electronic Information , Huazhong University of Science and Technology , Wuhan 430074 , China.
Wuhan National Laboratory for Optoelectronics , Huazhong University of Science and Technology , Wuhan 430074 , China.
ACS Nano. 2020 Feb 25;14(2):2156-2161. doi: 10.1021/acsnano.9b08975. Epub 2020 Jan 27.
Two-dimensional (2D) perovskites show great potential for optoelectronic applications due to their bandgap tunability, extremely large excition binding energy, and large crystal anisotropy compared with their three-dimensional counterparts. To fully explore exciton-based applications and improve their performance, it is essential to understand the exciton behavior in 2D perovskites. Here, we investigate exciton anisotropy within the crystallographic plane and cross plane of (CHNH)PbI 2D perovskite crystals by polarization-resolved photoluminescence, reflection, and photoconductivity studies. We observe a polarization-dependent emission evolution and an enhanced self-trapped exciton emission with an oblique incident excitation from the cross plane. Furthermore, the anisotropy of excitons in (CHNH)PbI 2D perovskite crystals is identified by polarization-resolved photoluminescence and photoconductivity measurement, and a completely opposite polarization-dependent behavior was observed for free excitons and self-trapped excitons. We attribute this different anisotropy to the existence of out-of-plane excitons and different optical selection rule for free excitons and self-trapped excitons. Our findings will shed light on designing and improving the performance of exciton-based optoelectronic devices in 2D perovskites.
与三维钙钛矿相比，二维（2D）钙钛矿因其带隙可调性、极大的激子结合能和较大的晶体各向异性，在光电器件应用方面展现出巨大潜力。为了充分探索基于激子的应用并提高其性能，了解二维钙钛矿中的激子行为至关重要。在此，我们通过偏振分辨光致发光、反射和光电导研究，研究了（CHNH）PbI二维钙钛矿晶体在晶面内和晶面间的激子各向异性。我们观察到偏振依赖的发射演化，以及从晶面间以斜入射激发时增强的自陷激子发射。此外，通过偏振分辨光致发光和光电导测量确定了（CHNH）PbI二维钙钛矿晶体中激子的各向异性，并且观察到自由激子和自陷激子呈现出完全相反的偏振依赖行为。我们将这种不同的各向异性归因于面外激子的存在以及自由激子和自陷激子不同的光学选择规则。我们的研究结果将为设计和提高二维钙钛矿中基于激子的光电器件性能提供启示。
