Over 21% Efficiency Stable 2D Perovskite Solar Cells

Abstract

Owing to the insufficient light absorption and charge transport, two-dimensional(2D) Ruddlesden-Popper (RP) perovskites show the relatively low efficiency. Here, we fabricated the methylammonium(MA), formamidinum(FA) and FA/MA mixed 2D PSCs. Incorporating FA cations extends the absorption range and enhance the light absorption. Optical spectroscopy showed that FA cations substantially increased the portion of 3D-like phase to 2D phases, and XRD studies revealed that FA based 2D perovskite possessed an oblique crystal orientation. Nevertheless, the ultra-fast interphase charge transfer result in an extremely long carrier diffusion length (∼1.98 μm). Also, chloride additives effectively suppress the yellow δ-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 PCE over 20%. Specifically, the pure FA based 2D PSCs achieved 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 its initial efficiency at 85°C persistent heating after 1500 hrs. Our results unambiguously demonstrate that pure FA based 2D PSCs are promising to achieve comparable efficiency to the 3D perovskite, along with a better device stability. This article is protected by copyright. All rights reserved