Over 21% Efficiency Stable 2D Perovskite Solar Cells

Owing to their insufficient light absorption and charge transport, 2D Ruddlesden-Popper (RP) perovskites show relatively low efficiency. In this work, methylammonium (MA), formamidinum (FA), and FA/MA mixed 2D perovskite solar cells (PSCs) are fabricated. Incorporating FA cations extends the absorption range and enhances the light absorption. Optical spectroscopy shows that FA cations substantially increase the portion of 3D-like phase to 2D phases, and X-ray diffraction (XRD) studies reveal that FA-based 2D perovskite possesses an oblique crystal orientation. Nevertheless, the ultrafast interphase charge transfer results in an extremely long carrier-diffusion length (approximate to 1.98 mu m). Also, chloride additives effectively suppress the yellow delta-phase formation of pure FA-based 2D PSCs. As a result, both FA/MA mixed and pure FA-based 2D PSCs exhibit a greatly enhanced power conversion efficiency (PCE) over 20%. Specifically, the pure FA-based 2D PSCs achieve a record PCE of 21.07% (certified at 20%), which is the highest efficiency for low-dimensional PSCs (n <= 10) reported to date. Importantly, the FA-based 2D PSCs retain 97% of their initial efficiency at 85 degrees C persistent heating after 1500 h. The results unambiguously demonstrate that pure-FA-based 2D PSCs are promising for achieving comparable efficiency to 3D perovskites, along with a better device stability.

Automated summary

This study fabricated 2D perovskite solar cells incorporating FA, MA, and FA/MA, resulting in significantly enhanced light absorption and device stability. The introduction of FA cations increased the 3D-like phase relative to 2D phases and effectively suppressed the formation of the yellow delta phase.