Photoinduced Giant Dielectric Constant in Lead Halide Perovskite Solar Cells

TLDR

Lead halide perovskites are a leading photovoltaic material, achieving up to 17.9% efficiency. The study investigates whether structural fluctuations drive the giant dielectric constant observed in these materials. Photoexcited carriers shift the local unit‑cell equilibrium and polarizability, aided by the rotational freedom of the methylammonium cation. The material shows a giant dielectric constant (~1000) that rises linearly with illumination intensity up to 1000× under 1 sun, a property intrinsic to MAPbX3 that sheds light on high‑efficiency perovskite operation.

Abstract

Organic–inorganic lead trihalide perovskites have emerged as an outstanding photovoltaic material that demonstrated a high 17.9% conversion efficiency of sunlight to electricity in a short time. We have found a giant dielectric constant (GDC) phenomenon in these materials consisting on a low frequency dielectric constant in the dark of the order of ε0 = 1000. We also found an unprecedented behavior in which ε0 further increases under illumination or by charge injection at applied bias. We observe that ε0 increases nearly linearly with the illumination intensity up to an additional factor 1000 under 1 sun. Measurement of a variety of samples of different morphologies, compositions, and different types of contacts shows that the GDC is an intrinsic property of MAPbX3 (MA = CH3NH3+). We hypothesize that the large dielectric response is induced by structural fluctuations. Photoinduced carriers modify the local unit cell equilibrium and change the polarizability, assisted by the freedom of rotation of MA. The study opens a way for the understanding of a key aspect of the photovoltaic operation of high efficiency perovskite solar cells.