  Recently, layered hybrid perovskites have been attracting huge interest due
to a wide range of possible chemical compositions and the resulting tunability
of the materials properties. In this study, we investigate the effect of the
chain length of the organic ligands on the optical properties of stacks of two
dimensional perovskite layers consisting of alkylammonium lead iodide
(CnH2n+1NH3)2PbI4 with n=4-18. Photoluminescence and absorption spectroscopy
reveal a blueshift with increasing chain length n including a jump of 110 meV
between the n=10 and n=12 ligands due to a change in octahedral tilting. Using
Xray diffraction (XRD) we determine the crystal structure and find the
octahedral tilting to be the main cause of this blueshift. However, for very
short chain lengths additional effects further reduce the transition energy.
Results of effective mass approximation model calculations show good agreement
between the expected reduction of transition energy and measured
photoluminescence emission wavelength for these samples. This highlights how
octahedral tilting plays a major role in determining the optical bandgap and
suggests that miniband formation plays only a minor role in this material.
