Photoinduced Giant Dielectric Constant in Lead Halide Perovskite Solar Cells

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.

Tunable ferroelectric polarization and its interplay with spin–orbit coupling in tin iodide perovskites

“…Finally, one may envisage the photocurrent being used to extract direct information on the different SOC-induced contributions, such as Rashba and Dresselhaus terms, for example, by means of the photogalvanic effect 39 . All these facts could have interesting applications benefiting from the peculiar electronic and photovoltaic properties of the material, thus opening the possibility of development of new optoelectronic devices 19 .…”

“…A full understanding of the hysteresis in (MA)PbI 3 is essential for further progress and is likely to lead to performance improvements 18,19 . However, green energy requirements pose serious constraints on the use of Pb-based materials, thus raising the question whether Pb could be replaced by nontoxic elements, such as Sn (refs 20-22).…”

Light-Induced Space-Charge Accumulation Zone as Photovoltaic Mechanism in Perovskite Solar Cells

“…5,6 However, the emergence and widespread observations of peculiar phenomena, including acute hysteresis in current density-voltage (J-V) curve, and switchability by voltage pretreatment, 7 indicate that the mechanisms that determine the performance of hybrid perovskite solar cells have not yet been understood. Here, we report the interpretation of the large capacitance under illumination 8,9 that reveals the origin of this feature. We suggest a large accumulation of majority carrier at the contact that indicates an unprecedented photovoltaic mechanism in the family of high performance solar cells.…”

“…9,14 In addition to the capacitive properties in dark, the low frequency capacitance increases rapidly under photogeneration of carriers. 8 It is therefore reasonable to assume that such capacitance is enhanced by electronic phenomena, requiring a different explanation from the ionic polarization observed in dark conditions. Overall, the large low-frequency capacitance observed to rise under illumination is believed to play a major role in performance via contact modification, 15 but a detailed understanding of the mechanism, whereby the capacitance displays such extraordinary rise in a solar cell, has not been stated before.…”

Formation and Diffusion of Metal Impurities in Perovskite Solar Cell Material CH3NH3PbI3: Implications on Solar Cell Degradation and Choice of Electrode

“…The low defect formation energies in MAPbI 3 indicate that the energy cost for bond breaking and distortion is low, which further implies low defect diffusion barriers. Indeed, fast diffusion of native defects in MAPbI 3 14, 17, 18, 19, 20, 21, 22, 23, 24, 25 and the resulting phenomena (such as hysteresis in current–voltage curves,25, 26, 27, 28 giant dielectric constant,28, 29 switchable photovoltaic effect,17 photon‐induced phase separation,30 etc.) have been reported and extensively discussed in the literature.…”