Publication date: 23rd October 2020
The partial incorporation of large organic cations (A-site cation engineering) into the octahedral sites of the three-dimensional (3D) perovskites has been widely investigated in films to optimize the performance of solar cell devices. However, the very few works reporting on the addition of large organic A-site cations in two-dimensional (2D) Ruddlesden-Popper (RP) perovskites have focused their attention on single crystals with low dimensionality (n = 2 and 3). Here, we have studied the gradual substitution of the methylammonium (MA) cation in thin films of 2D RP (BA)2(MA)2Pb3I10 perovskites (BA = n-butylammonium) by guanidinium (Gua), dimethylammonium (DA), ethylammonium (EA), rubidium (Rb), propylammonium (PA) or cesium (Cs) to synthesize mixed A-cation (BA)2(MA1-xAx)2Pb3I10 perovskites. Our experimental results allow us to determine the percentage limit at which the A-site cation is homogeneously incorporated in all n phases without destabilizing the overall structure. Grazing Incidence Wide-Angle X-ray Scattering (GIWAXS) measurements reveal the loss of the preferential orientation of the crystallites in the films at percentages above the threshold. The addition of percentages above the limit reveals the preferential insertion of the A-cation in the low dimensional phases (n = 2 and 3) with relaxed Goldschmidt tolerance factors. The steady-state and time-resolved absorption and photoluminescence (PL) measurements show that the structural changes in the 2D RP perovskites may lead to modifications of the optoelectronic properties, as larger bandgap (with EA), blue-shift of the PL peak position (above the threshold), strong quenching of the PL (with Cs) or reduced concentration of trap states (with Gua and EA). The extensive characterization of the newly prepared mixed A-cation 2D RP perovskite films can be very valuable to correlate the size and shape of the A-cation with the changes of the properties.
This work was financially supported by the Ministerio de Economía y Competitividad (MINECO) through project CTQ2017-84221-R
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