3 research outputs found

    Hindered Formation of Photoinactive δ‑FAPbI<sub>3</sub> Phase and Hysteresis-Free Mixed-Cation Planar Heterojunction Perovskite Solar Cells with Enhanced Efficiency via Potassium Incorporation

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    Organic–inorganic hybrid lead halide perovskite solar cells have demonstrated competitive power conversion efficiency over 22%; nevertheless, critical issues such as unsatisfactory device stability, serious current–voltage hysteresis, and formation of photo nonactive perovskite phases are obstacles for commercialization of this photovoltaics technology. Herein we report a facial yet effective method to hinder formation of photoinactive δ-FAPbI<sub>3</sub> and hysteresis behavior in planar heterojunction perovskite solar cells based on K<sub><i>x</i></sub>(MA<sub>0.17</sub>FA<sub>0.83</sub>)<sub>1–<i>x</i></sub>PbI<sub>2.5</sub>Br<sub>0.5</sub> (0≤ <i>x</i> ≤ 0.1) through incorporation of potassium ions (K<sup>+</sup>). X-ray diffraction patterns demonstrate formation of photoinactive δ-FAPbI<sub>3</sub> was almost completely suppressed after K<sup>+</sup> incorporation. Density functional theory calculation shows K<sup>+</sup> prefers to enter the interstitial sites of perovskite lattice, leading to chemical environmental change in the crystal structure. Ultrafast transient absorption spectroscopy has revealed that K<sup>+</sup> incorporation leads to enhanced carrier lifetime by 50%, which is also confirmed by reduced trap-assisted recombination of the perovskite solar cells containing K<sup>+</sup> in photovoltage decay. Ultraviolet photoelectron spectroscopy illustrates that K<sup>+</sup> incorporation results in a significant rise of conduction band minimum of the perovskite material by 130 meV, leading to a more favorable energy alignment with electron transporting material. At the optimal content of 3% K<sup>+</sup> (molar ratio, relative to the total monovalent cations), nearly hysteresis-free, enhanced power conversion efficiencies from 15.72% to 17.23% were obtained in this solar cell

    Tunable Crystallization and Nucleation of Planar CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> through Solvent-Modified Interdiffusion

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    A smooth and compact light absorption perovskite layer is a highly desirable prerequisite for efficient planar perovskite solar cells. However, the rapid reaction between CH<sub>3</sub>NH<sub>3</sub>I methylammonium iodide (MAI) and PbI<sub>2</sub> often leads to an inconsistent CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> crystal nucleation and growth rate along the film depth during the two-step sequential deposition process. Herein, a facile solvent additive strategy is reported to retard the crystallization kinetics of perovskite formation and accelerate the MAI diffusion across the PbI<sub>2</sub> layer. It was found that the ultrasmooth perovskite thin film with narrow crystallite size variation can be achieved by introducing favorable solvent additives into the MAI solution. The effects of dimethylformamide, dimethyl sulfoxide, γ-butyrolactone, chlorobenzene, and diethyl ether additives on the morphological properties and cross-sectional crystallite size distribution were investigated using atomic force microscopy, X-ray diffraction, and scanning electron microscopy. Furthermore, the light absorption and band structure of the as-prepared CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> films were investigated and correlated with the photovoltaic performance of the equivalent solar cell devices. Details of perovskite nucleation and crystal growth processes are presented, which opens new avenues for the fabrication of more efficient planar solar cell devices with these ultrasmooth perovskite layers

    The Influence of the Work Function of Hybrid Carbon Electrodes on Printable Mesoscopic Perovskite Solar Cells

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    In printable mesoscopic perovskite solar cells (PSCs), carbon electrodes play a significant role in charge extraction and transport, influencing the overall device performance. The work function and electrical conductivity of the carbon electrodes mainly affect the open-circuit voltage (<i>V</i><sub>OC</sub>) and series resistance (<i>R</i><sub>s</sub>) of the device. In this paper, we propose a hybrid carbon electrode based on a high-temperature mesoporous carbon (m-C) layer and a low-temperature highly conductive carbon (c-C) layer. The m-C layer has a high work function and large surface area and is mainly responsible for charge extraction. The c-C layer has a high conductivity and is responsible for charge transport. The work function of the m-C layer was tuned by adding different amounts of NiO, and at the same time, the conductivities of the hybrid carbon electrodes were maintained by the c-C layer. It was supposed that the increase of the work function of the carbon electrode can enhance the <i>V</i><sub>OC</sub> of printable mesoscopic PSCs. Here, we found the <i>V</i><sub>OC</sub> of the device based on hybrid carbon electrodes can be enhanced remarkably when the insulating layer has a relatively small thickness (500–1000 nm). An optimal improvement in <i>V</i><sub>OC</sub> of up to 90 mV could be achieved when the work function of the m-C was increased from 4.94 to 5.04 eV. When the thickness of the insulating layer was increased to ∼3000 nm, the variation of <i>V</i><sub>OC</sub> as the work function of m-C increased became less distinct
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