CsSnI3: Semiconductor or Metal? High Electrical Conductivity and Strong Near-Infrared Photoluminescence from a Single Material. High Hole Mobility and Phase-Transitions
CsSnI3: Semiconductor or Metal? High Electrical Conductivity and Strong Near-Infrared Photoluminescence from a Single Material. High Hole Mobility and Phase-Transitions
复制标题
DOI：
10.1021/ja301539s
复制
发表时间：
2012-05-23
影响因子：
15
通讯作者：
Kanatzidis, Mercouri G.
中科院分区：
文献类型：
--
作者：
Chung, In;Song, Jung-Hwan;Kanatzidis, Mercouri G.
CsSnI3是一种特殊的钙钛矿，在室温下经历了复杂的位移和重构相变，并表现出近红外发射。由于缺乏详细的晶体结构表征和化学不稳定性，CsSnI3的实验和理论研究一直受到限制。本文结合第一性原理密度泛函理论(DFT)计算，描述了CsSnI3纯晶型晶体的合成，大尺寸无裂纹/无气泡晶体的制备，CsSnI3的精细单晶结构以及随温度变化的电荷输运和光学性质。原位单晶和同步辐射粉末X射线衍射研究揭示了CsSnI3多晶型相变的起源。CsSnI3的黑色正交形显示了无机固体的最大体积热膨胀系数之一。电导率、霍尔效应和热电势测量表明，尽管其光学带隙为1.3 eV，但具有低载流子密度的p型金属行为。霍尔效应测量表明，CsSnI3为p型直接带隙半导体，室温载流子浓度约为10(17)cm(-3)，空穴迁移率约为585 cm(2)V-1 S(-1)。在具有类似带隙的p型半导体中，空穴迁移率是最高的之一。它的粉末在950 nm处具有很强的室温近红外发射光谱。值得注意的是，随着热处理时间的延长，薄膜的电导率和光致发光强度都增大。密度泛函理论计算表明，屏蔽化交换局域密度近似得到的带隙与实验测量的带隙符合得很好。对缺陷形成能的计算有力地表明，这种电学和发光性质可能是由晶体结构中的锡缺陷引起的，这种缺陷是内在存在的。因此，虽然化学计量比的CsSnI3是一种半导体，但这种材料容易产生与锡空位相关的本征缺陷。这会产生高度可移动的孔洞，使材料看起来像金属。
CsSnI3 is an unusual perovskite that undergoes complex displacive and reconstructive phase transitions and exhibits near-infrared emission at room temperature. Experimental and theoretical studies of CsSnI3 have been limited by the lack of detailed crystal structure characterization and chemical instability. Here we describe the synthesis of pure polymorphic crystals, the preparation of large crack-/bubble-free ingots, the refined single-crystal structures, and temperature-dependent charge transport and optical properties of CsSnI3, coupled with ab initio first-principles density functional theory (DFT) calculations. In situ temperature-dependent single-crystal and synchrotron powder X-ray diffraction studies reveal the origin of polymorphous phase transitions of CsSnI3. The black orthorhombic form of CsSnI3 demonstrates one of the largest volumetric thermal expansion coefficients for inorganic solids. Electrical conductivity, Hall effect, and thermopower measurements on it show p-type metallic behavior with low carrier density, despite the optical band gap of 1.3 eV. Hall effect measurements of the black orthorhombic perovskite phase of CsSnI3 indicate that it is a p-type direct band gap semiconductor with carrier concentration at room temperature of similar to 10(17) cm(-3) and a hole mobility of similar to 585 cm(2) V-1 s(-1). The hole mobility is one of the highest observed among p-type semiconductors with comparable band gaps. Its powders exhibit a strong room-temperature near-IR emission spectrum at 950 nm. Remarkably, the values of the electrical conductivity and photoluminescence intensity increase with heat treatment. The DFT calculations show that the screened-exchange local density approximation-derived band gap agrees well with the experimentally measured band gap. Calculations of the formation energy of defects strongly suggest that the electrical and light emission properties possibly result from Sn defects in the crystal structure, which arise intrinsically. Thus, although stoichiometric CsSnI3 is a semiconductor, the material is prone to intrinsic defects associated with Sn vacancies. This creates highly mobile holes which cause the materials to appear metallic.