  There is a variety of possible ways to tune the optical properties of 2D
perovskites, though the mutual dependence between different tuning parameters
hinders our fundamental understanding of their properties. In this work we
attempt to address this issue for (C$_n$H$_{2n+1}$NH$_3$)$_2$PbI$_4$ (with
n=4,6,8,10,12) using optical spectroscopy in high magnetic fields up to 67T.
Our experimental results, supported by DFT calculations, clearly demonstrate
that the exciton reduced mass increases by around 30% in the low temperature
phase. This is reflected by a 2-3 fold decrease of the diamagnetic coefficient.
Our studies show that the effective mass, which is an essential parameter for
optoelectronic device operation, can be tuned by the variation of organic
spacers and/or moderate cooling achievable using Peltier coolers. Moreover, we
show that the complex absorption features visible in absorption/transmission
spectra track each other in magnetic field providing strong evidence for the
phonon related nature of the observed side bands.
