Effect of guanidinium on the optical properties and structure of the methylammonium lead halide perovskite

The stability and performance of perovskite-based solar cells can be improved by changing the nature of the organic cation. Herein, mixed methylammonium-guanidinium perovskites (MA(1-x)GA(x)PbI(3)) are structurally and optically characterized. The Pawley fit method confirmed the formation of the iodide halide GAPbI(3) tetragonal phase (P42_NMC). Up to 20% of the guanidinium cation was incorporated in the methylammonium lead iodide perovskite, producing a lattice enlargement, which was investigated studying the shift of the diffraction peaks of the MAPbI(3) (I4_CM) tetragonal lattice. Long-term stability was tested, resulting in improved mixed perovskites with a low GA content. The bandgap shifted to lower energies. The absorption bandgap diminished slightly when the GA cation substituted up to 20% of MA in MAPbI(3), degrading when the GA amount in the mixed perovskite is larger. FESEM morphological analysis was performed showing that a uniform thin film was deposited. PL studies showed that only shallow defects had been introduced. (C) 2017 Elsevier B.V. All rights reserved.