Journal
ADVANCED ENERGY MATERIALS
Volume 10, Issue 14, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/aenm.201903900
Keywords
2D materials; DFT calculations; perovskites; photoelectron spectroscopy; quantum wells
Categories
Funding
- US-Israel Binational Science Foundation [2014357]
- Georgia Research Alliance
- ONR [N00014-17-1-2208]
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Reduced dimensionality forms of perovskites with alternating layers of organic ligands are a promising class of materials for achieving stable perovskite solar cells. Most work until now has focused on phases utilizing two ammonium terminated ligands per formula unit. However, phases utilizing a single diammonium ligand per formula unit are advantageous in that they can potentially have a thinner insulating organic layer between Pb-halide layers, yet the structural effects on their optoelectronic properties are not yet well understood. In this study two organic ligands, butane 1,4-diammonium (BDA) and N,N-dimethylpropane diammonium (DMPD), are investigated as spacers in n = 1, 2D perovskites. Using ultraviolet and inverse photoelectron spectroscopies, BDAPbI(4) is shown to have a larger transport gap by 350 meV and a larger exciton binding energy by 140 meV than DMPDPbI4. Through density functional theory calculations, the cause of this difference is traced to the out-of-plane tilting of the Pb-halide octahedra provoked by the asymmetric ligand in DMPDPbI4. Parallel channels of nearly straight Pb-I-Pb bonds are formed in one direction, leading to enhanced electronic coupling and higher band dispersion in that direction. In BDAPbI(4), no such channels exist, resulting in greater electronic confinement and a larger bandgap and exciton binding energy.
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