Quantifying and Reducing Ion Migration in Metal Halide Perovskites through Control of Mobile Ions

Abstract

The presence of intrinsic ion migration in metal halide perovskites (MHPs) is one of the main reasons that perovskite solar cells (PSCs) are not stable under operation. In this work, we quantify the ion migration of PSCs and MHP thin films in terms of mobile ion concentration (No) and ionic mobility (µ) and demonstrate that No has a larger impact on device stability. We study the effect of small alkali metal A-site cation additives (e.g., Na+, K+, and Rb+) on ion migration. We show that the influence of moisture and cation additive on No is less significant than the choice of top electrode in PSCs. We also show that No in PSCs remains constant with an increase in temperature but μ increases with temperature because the activation energy is lower than that of ion formation. This work gives design principles regarding the importance of passivation and the effects of operational conditions on ion migration.

Post‐Synthetic Interstitial Metal Doping for Efficient and Stable 3D/2D Heterostructured Perovskite Solar Cells

“…Beyond the XPS test, we also measured the mobile ion concentration of 3D/2D PSCs without and with doping different concentrations of ZnI 2 across various temperatures (Figure S12, Supporting Information). [ 24 ] It is shown that the average mobile ion concentration of devices decreased from 1.46×10 15 cm −3 for the 3D/2D PSCs to 4.27×10 13 cm −3 for the ZIM 3D/2D PSCs at room temperature of 300K, indicating the significantly suppressed ion migration within device when Zn 2+ was interstitially doped into perovskite lattice. Besides, compared with the 3D/2D device, the Zn 2+ doped 3D/2D device (especially the ZIM 3D/2D PSCs and 6 mM ZnI 2 doped 3D/2D PSCs) could maintain a relatively lower concentration level of mobile ions when samples were measured at higher temperatures (305K to 330K), indicating the validation of Zn 2+ in PSCs for suppressing ion migration behavior under heat.…”

“…Temperature‐dependent mobile ion concentration measurements were performed using the temperature control stage and module (T96) from Linkam, integrated with PAIOS. [ 24 ] Cross‐sectional scanning electron microscopy (SEM) images were taken utilizing a field‐emission scanning electron microscope (FE‐SEM, JEOL 7001). The XPS spectrum was tested using Krato Ultra by utilizing an Al Kα radiation source.…”

Use of carbon electrodes to reduce mobile ion concentration and improve reliability of metal halide perovskite photovoltaics

“…The main reason for their lack of widespread use in industry is their limited lifespan. PSCs in their current form degrade more quickly to replace silicon-based solar cells at the consumer level but there is ongoing research into the underlying mechanisms that cause this degradation including ion migration [5][6][7] .…”