(C₆H₅C₂H₄NH₃)₂GeI₄: A Layered Two-Dimensional Perovskite with Potential for Photovoltaic Applications

Abstract

Recently, two-dimensional organic-inorganic perovskites have attracted increasing attention due to their unique photophysical properties and high stability. Here we report a lead-free, two-dimensional perovskite, (PEA)GeI (PEA = CH(CH)NH). Structural characterization demonstrated that this 2D perovskite structure is formed with inorganic germanium iodide planes separated by organic PEAI layers. (PEA)GeI has a direct band gap of 2.12 eV, in agreement with 2.17 eV obtained by density functional theory (DFT) calculations, implying that it is suitable for a tandem solar cell. (PEA)GeI luminesces at room-temperature with a moderate lifetime, exhibiting good potential for photovoltaic applications. In addition, 2D (PEA)GeI is more stable than 3D CHNHGeI in air, owing to the presence of a hydrophobic organic long chain. This work provides a direction for the development of 2D Ge-based perovskites with potential for photovoltaic applications.

Progress and Perspective in Low‐Dimensional Metal Halide Perovskites for Optoelectronic Applications

“…Layered crystal structure of (a) (C n H 2 n +1 NH 3 ) 2 PbI 4 ( n = 18) with bulk alkylammonium cation. Reproduced with permission, Copyright 2010, American Chemical Society, (b) (C 6 H 11 NH 3 ) 2 PbBr 4 with cycloalkylammonium cation, Reproduced with permission, Copyright 2009, the Royal Society of Chemistry, (c) (NH 4 ) 3 Sb 2 I 9 single crystal with trivalent antimony cation, Reproduced with permission, Copyright 2017, Wiley‐VCH, (d) MA 2 CuCl 2 Br 2 with divalent copper cation, Reproduced with permission, Copyright 2015, American Chemical Society, (e) (C 6 H 5 C 2 H 4 NH 3 ) 2 GeI 4 with divalent germanium cation, Reproduced with permission, Copyright 2017, American Chemical Society, (f) MA 2 Pb(SCN) 2 I 2 with thiocyanate anion, Reproduced with permission, Copyright 2016, American Chemical Society.…”

“…Furthermore, with different organic cations, a series of copper‐based layered perovskites with various large organic cations including (CH 3 CH 2 CH 2 CH 2 NH 3 ) 2 CuBr 4 , (C 5 H 9 NH 3 ) 2 CuBr 4 , (C 6 H 5 CH 2 CH 2 NH 3 ) 2 CuCl 4 , (C 8 NH 6 CH 2 CH 2 NH 3 ) 2 CuCl 4 are explored with ferromagnetic and photovoltaic applications (Figure d) . In addition, ferrous perovskite (CH 3 NH 3 ) 2 Fe(II)Cl 4 and germanium‐containing perovskite (C 6 H 5 C 2 H 4 NH 3 ) 2 GeI 4 (Figure e) also tend to form layered structures, due to the similarity in their ionic radii of metal cations …”

Lead-free hybrid perovskites for photovoltaics

“…(a,b) Reprinted with permission from [140], copyright 2015 The Royal Society of Chemistry; (c) Reprinted with permission from [143], copyright 2017 American Chemical Society.…”

“…In particular, by introducing cations that are more bulky than MA + , such as phenylethylamine (PEA) cation C 6 H 5 (CH 2 ) 2 NH 3 + , a layered structure can be formed with inorganic germanium iodide layers separated by organic PEA layers (Fig. 9) [143]. The (PEA) 2 GeI 4 HP revealed a direct bandgap of 2.12 eV making it suitable for tandem solar cells.…”

“…The (PEA) 2 GeI 4 HP revealed a direct bandgap of 2.12 eV making it suitable for tandem solar cells. This layered perovskite was also found to be much more stable in humid air than MAGeI 3 because of its high hydrophobicity of the organic component [143]. …”