Iodine interstitials as a cause of nonradiative recombination in hybrid perovskites

The identification of deep-level defects that act as detrimental nonradiative recombination centers is critical for optimizing the optoelectronic performance of hybrid perovskites. Although extensive studies have been devoted to revealing the nature of deep-level defects in hybrid perovskites, it is still unclear what defects are responsible for the experimentally observed nonradiative recombination rates. Employing first-principles approaches, we quantitatively show that the iodine interstitial is a dominant nonradiative recombination center in methylammonium-lead iodide. This important insight points to a target for defect engineering in order to further improve the performance of hybrid perovskites.

Figure 1

Formation energy of the iodine interstitial, ${\mathrm{I}}_i$, as a function of the Fermi level under I-rich conditions. The $(0/-)$ charge-state transition occurs at 0.78 eV above the valence-band maximum (VBM), and the $(+/0)$ transition at 0.48 eV below the conduction-band minimum (CBM).

Figure 2

Local atomic structures of ${\mathrm{I}}_i$ in three charge states ($+$, 0, and $-$). The arrows and labels show the relevant carrier capture processes. In the labels of capture coefficients, the subscript denotes the carrier being captured ($n$ for electrons and $p$ for holes) while the superscript denotes the charge state of the initial configuration. The green dashed circles highlight the location of the I interstitials.

Figure 3

Configuration coordinate diagram for (a) the $(+/0)$ and (b) the $(0/-)$ charge-state transitions of the iodine interstitial.

Figure 4

(a) Nonradiative capture coefficients of ${\mathrm{I}}_i$ as a function of temperature. (b) Nonradiative recombination coefficient $A$ of ${\mathrm{I}}_i$ as a function of temperature for three different defect densities (${10}^{14}$, ${10}^{15}$, and ${10}^{16}{\mathrm{cm}}^{-3}$). The black circles in (b) correspond to the experimental $A$ coefficients reported in the literature [10, 11, 12, 13, 14].