Gert-Jan Wetzelaer1,Mohammad Sajedi Alvar1,Paul Blom1
Max Planck Institute for Polymer Research1
Gert-Jan Wetzelaer1,Mohammad Sajedi Alvar1,Paul Blom1
Max Planck Institute for Polymer Research1
Hybrid organic-inorganic perovskites are promising materials for the application in solar cells and light-emitting diodes. However, the basic current-voltage behavior for electrons and holes is still poorly understood in these semiconductors due to their mixed electronic-ionic character. To develop an experimentally-validated numerical device model, it is therefore necessary to isolate individual physical phenomena. We investigate the dynamics of ion motion in methyl ammonium lead iodide (MAPbI<sub>3</sub>) by impedance spectroscopy and electric displacement as a function of frequency. The displacement response is fully reproduced by a numerical device model that enables us to determine the frequency-dependent dielectric constant, the ion concentration and the ion diffusion coefficient. These validated ion dynamics are applied to analyze space-charge-limited electron and hole currents in MAPbI<sub>3</sub>. We demonstrate that the frequency dependence of the permittivity plays a crucial role in the analysis of space-charge-limited currents and their dependence on voltage scan rate [1]. Our mixed electronic-ionic device model accurately reproduces the current-voltage characteristics of single-carrier devices, showing that in MAPbI<sub>3</sub> transport of electrons dominates over holes. Furthermore, the direction of the hysteresis reveals the sign of the mobile ionic species. Knowing the ion dynamics and charge-transport properties, we demonstrate that in MAPbI<sub>3</sub> solar cells, the light-enhanced and frequency-dependent permittivity is of crucial importance for the device characteristics, importantly reducing charge recombination in the solar cell. As a result, we demonstrate that the current-voltage characteristics of perovskite solar cells can be fully described with a device model that contains only experimentally validated input parameters.<br/>References:<br/>[1] Sajedi Alvar, M., Blom, P.W.M. & Wetzelaer, GJ.A.H. Space-charge-limited electron and hole currents in hybrid organic-inorganic perovskites. <i>Nat Commun</i> 11, 4023 (2020). https://doi.org/10.1038/s41467-020-17868-0