Mechanochromism of layered perovskites

Optical and structural properties of 2D layered Ruddlesden-Popper and Dion-Jacobson perovskites were investigated under mild hydrostatic pressures (<0.5 GPa), to provide an insight into mechanochromic properties of these promising photovoltaic materials. Pb-halides with 1,4-phenylenedimethylammonium (PDMA) and benzylammonium (BzA) organic spacers experienced under pressure a reversible red shift of the UV-VIS spectra. The only non-centrosymmetric compound studied, (BzA)2PbBr4, undergoes an isostructural phase transition accompanied by negative area compressibility. The optical absorbance and bandgaps of all materials decrease with pressure, which implies that compression significantly affects the corresponding quantum confinements. This can be tuned by both the spacer size as well as the changes in the potential barrier width that can be effectively reduced by the relatively small, applied pressure.