Elucidation of the role of guanidinium incorporation in single-crystalline MAPbI3 perovskite on ion migration and activation energy.

Apurba Mahapatra,Janusz Lewiński,Suverna Trivedi,Pawan Kumar,Jan Nawrocki,Pankaj Yadav,Mohammad Mahdi Tavakoli,Rashmi Runjhun,Daniel Prochowicz,Abul Kalam

doi:10.1039/d0cp01119c

Abstract

Ion migration plays a significant role in the overall stability and power conversion efficiency of perovskite solar cells (PSCs). This process was found to be influenced by the compositional engineering of the A-site cation in the perovskite crystal structure. However, the effect of partial A-site cation substitution in a methylammonium lead iodide (MAPbI3) perovskite on the ion migration process and its activation energy is not fully understood. Here we study the effect of a guanidinium (GUA) cation on the ion transport dynamics in the single crystalline GUAxMA1-xPbI3 perovskite composition using temperature-dependent electrochemical impedance spectroscopy (EIS). We find that the small substitution of MA with GUA decreases the activation energy for iodide ion migration in comparison to pristine MAPbI3. The presence of a large GUA cation in the 3D perovskite structure induces lattice enlargement, which perturbs the atomic interactions within the perovskite lattice. Consequently, the GUAxMA1-xPbI3 crystal exhibits a higher degree of hysteresis during current-voltage (J-V) measurements than the single-crystalline MAPbI3 counterpart. Our results provide the fundamental understanding of hysteresis, which is commonly observed in GUA-based PSCs and a general protocol for in-depth electrical characterization of perovskite single crystals.

Highlights

The migration process of ions in perovskite films has been intensively studied using photo-thermal induced resonance (PTIR) microscopy,[18] temperature-dependent impedance spectroscopy,[19,20] Muon spin relaxation,[19] defect spectroscopy,[21] current–potential curves[22,23] and Kelvin probe force microscopy (c-KFM).[24]
We study the effect of GUA on ion transport in mixed-cation GUAxMA1ÀxPbI3 perovskite single crystals using temperature-dependent electrochemical impedance spectroscopy (EIS)
We attempted the synthesis of GUAxMA1ÀxPbI3 single crystals containing a higher GUA content by mixing PbI2, MAI and GUAI with the molar ratios of 1 : 0.7 : 0.3 and 1 : 0.6 : 0.4, but using the above-mentioned procedure, we failed to crystallize the materials as single crystals

Summary

Introduction

The migration process of ions in perovskite films has been intensively studied using photo-thermal induced resonance (PTIR) microscopy,[18] temperature-dependent impedance spectroscopy,[19,20] Muon spin relaxation (mSR),[19] defect spectroscopy,[21] current–potential curves[22,23] and Kelvin probe force microscopy (c-KFM).[24]. We study the effect of GUA on ion transport in mixed-cation GUAxMA1ÀxPbI3 perovskite single crystals using temperature-dependent electrochemical impedance spectroscopy (EIS). We show that the GUAxMA1ÀxPbI3 perovskite single crystals exhibit lower activation energy for the iodide ion migration than MAPbI3 single crystals.

Results

Conclusion