First-Principles Study of Ion Diffusion in Perovskite Solar Cell Sensitizers

Jun Haruyama; Keitaro Sodeyama; Liyuan Han; Yoshitaka Tateyama

doi:10.1021/jacs.5b03615

First-Principles Study of Ion Diffusion in Perovskite Solar Cell Sensitizers

J Am Chem Soc. 2015 Aug 19;137(32):10048-51. doi: 10.1021/jacs.5b03615. Epub 2015 Aug 10.

Authors

Jun Haruyama, Keitaro Sodeyama, Liyuan Han^{1

2}, Yoshitaka Tateyama²

Affiliations

¹ ∥Photovoltaic Materials Unit, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan.
² ⊥PRESTO and CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 333-0012, Japan.

PMID: 26258577
DOI: 10.1021/jacs.5b03615

Abstract

Hysteresis in current-voltage curves has been an important issue for conversion efficiency evaluation and development of perovskite solar cells (PSCs). In this study, we explored the ion diffusion effects in tetragonal CH3NH3PbI3 (MAPbI3) and trigonal (NH2)2CHPbI3 (FAPbI3) by first-principles calculations. The calculated activation energies of the anionic and cationic vacancy migrations clearly show that I(-) anions in both MAPbI3 and FAPbI3 can easily diffuse with low barriers of ca. 0.45 eV, comparable to that observed in ion-conducting materials. More interestingly, typical MA(+) cations and larger FA(+) cations both have rather low barriers as well, indicating that the cation molecules can migrate in the perovskite sensitizers when a bias voltage is applied. These results can explain the ion displacement scenario recently proposed by experiments. With the dilute diffusion theory, we discuss that smaller vacancy concentrations (higher crystallinity) and replacement of MA(+) with larger cation molecules will be essential for suppressing hysteresis as well as preventing aging behavior of PSC photosensitizers.