Effect of Crystal Grain Orientation on the Rate of Ionic Transport in Perovskite Polycrystalline Thin Films

Abstract

In this work, we examine the effect of microstructure on ion-migrationinduced photoluminescence (PL) quenching in methylammonium lead iodide perovskite films. Thin films were fabricated by two methods: spin-coating, which results in randomly oriented perovskite grains, and zone-casting, which results in aligned grains. As an external bias is applied to these films, migration of ions causes a quenching of the PL signal in the vicinity of the anode. The evolution of this PLquenched zone is less uniform in the spin-coated devices than in the zone-cast ones, suggesting that the relative orientation of the crystal grains plays a significant role in the migration of ions within polycrystalline perovskite. We simulate this effect via a simple Ising model of ionic motion across grains in the perovskite thin film. The results of this simulation align closely with the observed experimental results, further solidifying the correlation between crystal grain orientation and the rate of ionic transport.

Probing the ionic defect landscape in halide perovskite solar cells

“…Indeed, in our recent work, we demonstrated a distribution of migration rates for each of the reported defects 39 . This is also supported by a combined experimental-theoretical work, where modeling of ion migration induced PL quenching was only possible by applying a Gaussian distribution of ion migration rates 86 . 30,[34][35][36]38 (often called emission rates in the papers) were plotted in an Arrhenius diagram for comparison to our findings (species β (crosses), γ (circles), δ (stars)).…”

Gap States in Methylammonium Lead Halides: The Link to Dimethylsulfoxide?

“…Both the film made with DMSO ( Figure 4b) and alloyed film (Figure 4d) show significant density of gap states above the VBM. Mindful of the potential for variability in MAPbI 3 electronic structure as a function of processing, as demonstrated early on by many groups, [34][35][36][37][38] we repeated our measurements on four batches of MAPbI 3 films prepared independently, and obtained very consistent results. The smoothed satellite-corrected spectra of three batches of these MAPbI 3 films on TiO 2 , superimposed to better illustrate the differences induced by different additives, are presented in Figure S5, Supporting Information.…”

Shining Light on the Photoluminescence Properties of Metal Halide Perovskites

“…Complicating this measurement is the difficulty in assigning a definite position to the quenching front, as often it is rough and undefined. In a recent publication, [ 254 ] our group exploited the grain microstructure uniformity of zone‐cast perovskite ribbons to make extremely precise measurements of the quenching front progression, as seen in Figure . By fitting the position of the quenching front with respect to time, and using the applied external bias of 0.9 V µm −1 , we were able to extract a mobility value 3.8 × 10 −9 cm 2 V −1 s −1 , leading to a diffusion coefficient of 9.8 × 10 −11 cm 2 s −1 , in good agreement with the reported values.…”