Pressure-Induced Polymorphic, Optical, and Electronic Transitions of Formamidinium Lead Iodide Perovskite

Abstract

Formamidinium lead iodide (FAPbI) perovskite as a superior solar cell material was investigated in two polymorphs at high pressures using in situ synchrotron X-ray diffraction, FTIR spectroscopy, photoluminescence (PL) spectroscopy, electrical conductivity (EC) measurements, and ab initio calculations. We identified two new structures (i.e., Imm2 and Immm) for α-FAPbI but only a structural distortion (in C2/c) for δ-FAPbI upon compression. A pressure-enhanced hydrogen bond plays a prominent role in structural modifications, as corroborated by FTIR spectroscopy. PL measurements and calculations consistently show the structure and pressure dependences of the band gap energies. Finally, EC measurements reveal drastically different transport properties of α- and δ-FAPbI at low pressures but a common trend to metallic states at high pressures. All of these observations suggest strongly contrasting structural stabilities and pressure-tuned optoelectric properties of the two FAPbI polymorphs.

Pressure‐Induced Emission Enhancement, Band‐Gap Narrowing, and Metallization of Halide Perovskite Cs3Bi2I9

“…The application of external hydrostatic pressure can modify bond length and bond angle in halide perovskites without altering the chemical composition, thereby finely tuning the electronic configuration with improved optical and electrical properties, such as narrowed band gap and prolonged carrier lifetime. [5] In recent years,three-dimensional halide perovskite has been comprehensively studied upon compression, and acquired ag reat deal of fundamental understanding of structureproperty relationships.Avariety of novel properties also have been discovered, including enhanced structural stability, piezochromism, and metallization. [5b, 6] High-pressure technique likes av ersatile tailor to modify various physical properties of the adaptable Cs 3 Bi 2 I 9 .T his approach provides af easible strategy to optimize its properties,s imultaneously, expanding the recognition and continuing research prospects of the zero-dimensional halide perovskite to satisfy current urgent needs.…”

CH3NH3PbI3 and HC(NH2)2PbI3 Powders Synthesized from Low‐Grade PbI2: Single Precursor for High‐Efficiency Perovskite Solar Cells

“…In the J-V curves, the solid and dashed lines representr everse-scanned and forward-scannedd ata, respectively, measuredunder AM 1.5G 1sun illumination at a scanr ate of 130 mV s À1 . [52] The steady-state PL spectra were measured and are compared in Figure 5b.T he PL intensities of the a-phaseF APbI 3 films are similar regardless of the precursors. FAPbI 3 thin films were prepared by spin coating solutions containing the FAPbI 3 powder or highgrade PbI 2 and FAI, and the as-deposited films were annealed at 145 8Cf or 40 min.…”

“…The absorbance of the d-phaseF APbI 3 film obtainedf rom the black a-phaseF APbI 3 powder is significantly blueshifted relative to the film obtained from the pure d-phase powder.F rom the Tauc plot based on ad irect band gap transition model, the band gap was determined to be approximately 1.5 eV for the FAPbI 3 film prepared from the d-phase powders, whereas the band gap of the FAPbI 3 film prepared from the a-phase powderw as approximately 2.4 eV,w hich corresponds to onedimensional d-phase FAPbI 3 . [52] The steady-state PL spectra were measured and are compared in Figure 5b.T he PL intensities of the a-phaseF APbI 3 films are similar regardless of the precursors. Interestingly,t he film prepared from the a/d mixed-phase powder (PbI 2 /FAI = 1:1.5) shows much higherP L intensity,and this may be due to the a/d phase junction.…”

Recent Advances in Energetics and Stability of Metal Halide Perovskites for Optoelectronic Applications

“…Changes in A‐site cation result in the stronger impact on electronic structures of perovskites. Formamidinium (FA) is widely used due to its appropriate ionic radius and superior thermal stability . The IP value of FAPbI 3 was measured to be 5.7 eV by Koh et al, 5.63 eV by Zhumekenov et al, or 5.4 eV by Pang et al, respectively.…”