1.SHU-SolarE R&D Laboratory, Shanghai Key Laboratory of High Temperature Superconductors, Department of Physics, Shanghai University, Shanghai 200444, China 2.State Key Laboratory of Surface Physics and Department of Physics, Key Laboratory of Micro and Nano Photonic Structure (Ministry of Education), Fudan University, Shanghai 200433, China 3.Department of Electronic Information Materials, Shanghai University, Shanghai 200444, China 4.School of Information Science and Technology, Fudan University, Shanghai 200433, China
Fund Project:Project supported by the Natural Science Foundation of Shanghai, China (Grant No. 17ZR1409600), the National Natural Science Foundation of China (Grant Nos. 61874027, 11527805, 61874070), and State Key Laboratory of Surface Physics of Fudan University, China (Grant No. KF2018_08)
Received Date:16 August 2019
Accepted Date:13 October 2019
Available Online:28 November 2019
Published Online:01 December 2019
Abstract:Lead halide perovskite has attracted much attention due to its high absorption coefficient, long carrier diffusion length, low binding energy, and low cost. The stability of intrinsic crystal structure in I-based perovskite can be theoretically estimated by calculating cubic structures factor and octahedral factor. Experimental methods to solve the stability of structure in I-based perovskite could be mainly to either incorporate anions (e.g. Cl–, Br–) or mix cations (e.g. Cs+) into I-based perovskite matrix. Moreover, incorporating Br– into I-based perovskite leads its band gap to widen, which might be used as a top-cell material to tandem solar cell. However, in order to understand photo-physics process of anion-mixed and/or cation-mixed perovskites, it is essential to further investigate the optical properties such as absorption spectrum, photoluminescence (PL), temperature-dependent PL (TPL) behavior, etc. In this work, anion-mixed and/or cation-mixed perovskite thin films with high quality crystallization and (110) prereferral orientation are synthesized by one-step solution method. All mixed perovskite films are characterized by using X-ray diffraction (Rigaku D MAX-3C, Cu-Kα, λ = 1.54050 ?) and X-ray photoelectron spectroscopy (XPS) (Thermo Scientific Escalab 250Xi). A set of strong peaks of the mixed perovskite films at 14.12° and 28.48°, is assigned to (110) and (220) lattice plane of orthorhombic crystal structure of I-based perovskite, due to preferred orientation. The Pb 4f and I 3d doublet peaks, corresponding to Pb+2 and I– states, are observed in XPS spectra. It should be noted that in the absence of other valence states of Pb and I component at lower/upper binding energy, the chemical element composition ratio of Pb+2 and I– are close to stoichiometric proportion. For optical absorptionspectra, the optical bandgaps of the perovskite films increase with doping concentration of Br– increasing. For TPL, the perovskite films with x = 0 and x = 0.05 show abnormal red-shifts in a temperature range from 10 to 100 K. The following blue shifts in a temperature range from 125 to 350 K emerge, which is mainly attributed to band gap widening. However, incorporating more Br– into I-based perovskite leads the TPL spectra to monotonically blue-shift. A linear relationship between the TPL peak position and the doping concentration of Br– ions is observed at the same temperatures. This indicates that the Br– anion in I-based perovskite plays a crucial role in determining the optical properties. The low-temperature and high-temperature (HT) excitonic binding energy at x = 0 are 186 meV and 37.5 meV, respectively. The HT excitonic binding energy first increases and then decreases with the Br– concentration in I-based perovskite film increasing. The minimal variation of TPL peak position and FWHM (full width at half maximum) at x = 0.0333 are 13 nm and (25.8 ± 0.5) meV, respectively, suggesting higher temperature stability in optical property. This should contribute to understanding the relationship between temperature-dependent electrical and optoelectronic performance for hybrid mixed perovskite materials and devices. Keywords:hybrid mixed perovskite/ temperature-dependent photoluminescence/ optical properties/ excitonic binding energy
图 1 (a) 阴离子混合型钙钛矿MAPb(BrxI1–x)3的XRD谱; (b) (110)和(220)衍射峰强和晶面间距d随Br–比例x的变化; (c) 不同Br–比例的钙钛矿薄膜中Pb和I元素XPS谱
图 2 室温下的阴离子混合型钙钛矿
图 3 室温下阴离子混合型钙钛矿MAPb(BrxI1–x)3 PL图谱 (a)归一化PL谱; (b)峰位和峰强与Br比例x的关系
图 4 阴离子混合型钙钛矿MAPb(BrxI1–x)3可见波段变温PL谱 (a) PL谱; (b) PL投影图; (c)通过Arrhenius拟合提取激子结合能; (d) PL的强度、峰位和半高宽
图 5 混合阳离子(Cs0.05(FA0.85MA0.15)0.95)Pb(Br0.15I0.85)3 薄膜 (a) PL谱; (b)归一化变温PL投影图; (c) 可见波段发光峰位和强度随温度的变化