Crystal Growth Regulation via Co-spacer Cations Mixed with Methylammonium in Lead Iodide in Perovskite Photovoltaics

In this work, we used co-spacer cations to control thephase distributionusing a mixture of benzylammonium (BZA) and guanidium (GA). We observedthat the crystal structure was different when the two-dimensional(2D) perovskite was prepared only with BZA and when the 2D perovskitewas prepared with a combination of BZA and GA. The perovskite filmprepared from these mixed cations demonstrated increased grain sizeand enhanced crystallinity from the BZA-based perovskite to the GA-basedperovskite. Thus, perovskite solar cells from these mixed cation perovskitesexhibit a power conversion efficiency (PCE) of 14.95-16.23%and the GA-based device shows a PCE of up to 18.31%. Our studies revealthat the size and the nature of the organic spacer cation are relatedto the overall stability of the corresponding lead iodide and suggestthat the phase distribution of the 2D perovskite is finely controlledby the mixture of two different large organic cations.