Pressure-Induced Phase Transitions and Bandgap-Tuning Effect of Methylammonium Lead Iodide Perovskite
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.154
Pressure-Induced Phase Transitions and BandgapTuning Effect of Methylammonium Lead Iodide Perovskite Shaojie Jiang,1 Yanan Fang,2 Ruipeng Li,3 Timothy J. White,2 Zhongwu Wang,3 Tom Baikie,2 and Jiye Fang1 1 Materials Science and Engineering Program, State University of New York at Binghamton, Binghamton, New York 13902, USA; 2Energy Research Institute@NTU, School of Materials Science and Engineering, Nanyang Technological University, Republic of Singapore; 3Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York 14853, USA
ABSTRACT
Pressure-induced crystallographic transitions and optical behavior of MAPbI3 (MA=methylammonium) were investigated using in-situ synchrotron X-ray diffraction and laser-excited photoluminescence spectroscopy. We observed that the tetragonal phase that presents under ambient pressure transformed to a ReO 3-type cubic phase at 0.3 GPa, which further converted into a putative orthorhombic structure at 2.7 GPa. The sample was finally separated into crystalline and amorphous fractions beyond 4.7 GPa. During the decompression, the phase-mixed material restored the original structure in two distinct pathways depending on the peak pressures. Being monitored using a laserexcited photoluminescence technique under each applied pressure, it was determined that the bandgap reduced with an increase of the pressure till 0.3 GPa and then enlarged with an increase of the pressure up to 2.7 GPa. This work lays the foundation for understanding pressure-induced phase transitions and bandgap tuning of MAPbI3, enriching potentially the toolkit for engineering perovskites related photovoltaic devices. Introduction The power conversion efficiency (PCE) of perovskite-based photovoltaic (PV) cells has a rapid increase from about 6% in 2011 to approximate 20% presently[1]. While modifying charge carrier mobility and the direct bandgap by tuning crystal chemistry can improve the PCE, extensive synthesis campaigns have revealed a limited range of materials[2]. Alternatively, pressurization is an effective and robust way to change the crystal structures and thus to guide strategies for selecting ions of appropriate size and charge by monitoring changes in PV properties[3]. The perovskite prototype has a general formula ABX3, creating a 3D framework with corner-sharing BX6 octahedra in which the A component provides charge compensation (Figure 1a). The bandgaps of Pbbased MA halide perovskites, MAPbCl3, MAPbBr3, and MAPbI3, were reported as ~3.1, ~2.3, and ~1.5 eV, respectively[4]. The appropriate bandgap for a single junction PV cell is within a range between 1.1 and 1.4 eV[5,6]. This indicates that MAPbI3 could be a desirable halide perovskite material to fundamentally understand the subject. Although previous studies of pressure-induced transformation in hybrid perovskites have validated
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