Intermediate Phase Intermolecular Exchange Triggered Defect Elimination in CH3NH3PbI3 toward Room-Temperature Fabrication of Efficient Perovskite Solar Cells

Low-Temperature Preparation of High-Quality Perovskite Polycrystalline Films via Crystallization Kinetics Engineering

Preparation of lead halide perovskite polycrystalline films at a low annealing temperature is highly restricted by their intrinsically large crystallization activation energy, which hinders the conversion of the precursors/intermediates to perovskites and yields as-prepared polycrystals with tiny grain sizes and terrible crystal quality. Herein, we demonstrate through in-situ, real-time spectroscopic studies that both the nucleation and crystal growth kinetics can be improved without the need for a high annealing temperature by treating the film with thiourea, as accounted for by the reduced activation energy. As a consequence, the thiourea-treated perovskite polycrystalline film exhibits larger grain sizes and greater crystallinity than the untreated one. More importantly, owing to the synergistic effect of the promoted crystallization kinetics and the passivation of surface defects, the low-temperature prepared films treated with thiourea even present more prominent photophysical properties than those fabricated by using the conventional high-temperature method. The strategy of crystallization kinetics engineering proposed in this work paves the way for fabricating high-quality perovskite polycrystalline films in a low-temperature manner.

Resistance Switching Effect of Memory Device Based on All-Inorganic Cspbbri2 Perovskite

In this study, the CsPbBrI₂ perovskite film was prepared by the preparation of the sol-gel and the spin-coating method, and the cubic lattice was stabilized by introducing Br⁺ into the CsPbI₃ film, which solved the problem of instability of the traditional perovskite phase. Based on the CsPbBrI₂ perovskite film, the Ag/CsPbBrI₂/ITO memory device with a resistance switching effect was prepared. The morphology and phase compositions of the film were analyzed by scanning electron microscope and X-ray diffraction. The non-volatile and repeatable resistance switching effect of the Ag/CsPbBrI₂/ITO memory device was measured under open-air conditions. The experimental results show that the surface of the CsPbBrI₂ perovskite film is uniform and dense, and the Ag/CsPbBrI₂/ITO memory device has an order of magnitude resistance-on-off ratio after 500 cycles of cyclic voltage. This study shows that Ag/CsPbBrI₂/ITO memory devices based on CsPbBrI₂ perovskite films have potential applications in the field of non-volatile memory devices. At the same time, the transient properties of the CsPbBrI₂ film that can quickly dissolve in deionized water make it potentially useful in short-period data storage units and implantable electronic devices with human or environmental sensors.

Template-Assisted Formation of High-Quality α-Phase HC(NH2)2PbI3 Perovskite Solar Cells

Formamidinium (FA) lead halide (α-FAPbI3) perovskites are promising materials for photovoltaic applications because of their excellent light harvesting capability (absorption edge 840 nm) and long carrier diffusion length. However, it is extremely difficult to prepare a pure α-FAPbI3 phase because of its easy transformation into a nondesirable δ-FAPbI3 phase. In the present study, a "perovskite" template (MAPbI3-FAI-PbI2-DMSO) structure is used to avoid and suppress the formation of δ-FAPbI3 phases. The perovskite structure is formed via postdeposition involving the treatment of colloidal MAI-PbI2-DMSO film with FAI before annealing. In situ X-ray diffraction in vacuum shows no detectable δ-FAPbI3 phase during the whole synthesis process when the sample is annealed from 100 to 180 °C. This method is found to reduce defects at grain boundaries and enhance the film quality as determined by means of photoluminescence mapping and Kelvin probe force microscopy. The perovskite solar cells (PSCs) fabricated by this method demonstrate a much-enhanced short-circuit current density (  J sc) of 24.99 mA cm-2 and a power conversion efficiency (PCE) of 21.24%, which is the highest efficiency reported for pure FAPbI3, with great stability under 800 h of thermal ageing and 500 h of light soaking in nitrogen.

Enhanced Performance of Perovskite Solar Cells with Zinc Chloride Additives

Perovskite solar cells (PSCs) have attracted extensive attention due to their impressive photovoltaic performance. The quality of the perovskite layer is very critical to achieve high device performance. Here, we explore the partial substitution of PbI₂ by ZnCl₂ in the preparation of CH₃NH₃PbI₃ and its effects on perovskite morphology, optical properties, and photovoltaic performance. Consequently, the device with 3% ZnCl₂ shows great improvement in power conversion efficiency (PCE) from 16.4 to 18.2% compared to that of the control device. Moreover, the device is more stable than the control device, with only 7% degradation after aging for 30 days. These results are attributed to the increased grain size, improved film morphology, and reduced recombination loss after the partial substitution of PbI₂ by ZnCl₂ in the perovskite film. This work develops a new approach for morphology control through rational additives in the perovskite film, and paves the way toward further enhancing the device performances of PSCs including PCE and stability.