Organic-inorganic hybrid perovskites have attracted the attention of researchers all over the world because of their excellent optoelectronic properties. As a solar cell prepared by the active layer, the photoelectric conversion efficiency has exceeded 25%, which is close to the highest value of the single crystal silicon battery. However, the perovskite thin film prepared by the low-temperature solution method is usually polycrystalline. Polycrystalline films, which are prone to defects at their surface and grain boundaries, will capture photo-generated charges, leading to additional non-radiative recombination energy loss, limiting the open circuit voltage and overall performance of the device. Passivation is an effective method to reduce defects and inhibit non-radiative recombination. Lewis base, PbI2, PMMA polymer materials, etc. have been successfully used to passivate the defects of perovskite. Among them, organic amine salts, such as phenethylamine iodine (PEAI), have also been successfully used to passivate the surface of perovskite to increase the open circuit voltage of the device. However, PEAI-treated perovskites are sensitive to temperature. At high temperatures, PEAI itself will react to form two-dimensional perovskites, affecting the stability of the device. In addition, the passivation mechanism of ammonium salts needs more research.
Gao Peng's research group at the Key Laboratory of Functional Nanostructure Design and Assembly, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences used a large volume of 1-naphthylmethyl iodide (NMAI) to passivate the perovskite surface interface. Like PEAI, NMAI is mixed with PbI2 in a strong polar dimethylformamide (DMF) solution and spin-coated in one step to form 2D perovskite, and has been successfully used to prepare efficient 2D / 3D perovskite LEDs Device. However, NMAI shows different properties from PEAI when post-processing the 3D perovskite film in a weak polar isopropyl alcohol (IPA) solution. XRD tests show that even at high temperatures up to 100 ° C, most of the ammonium salt on the surface of the treated 3D perovskite film does not participate in the ion exchange reaction, and only a very small amount of 2D perovskite is formed. Therefore, in a complete battery device, the NMAI layer between the perovskite and the hole transport layer has the following synergistic passivation effects: First, the zwitterionic nature of NMAI itself can passivate the surface ions of the perovskite Defects; Secondly, NMAI interacts with the perovskite surface to form an interface dipole, which induces vacuum level bending, thereby improving the energy band matching of the interface; and finally, the insulating NMAI can function as an electron barrier. The multiple passivation effects of the NMAI layer make the prepared perovskite battery devices exhibit higher electroluminescence efficiency, which strongly indicates that the non-radiative recombination at the interface between the perovskite and the hole transport layer is greatly reduced. Under a standard sunlight, the open circuit voltage of the device reaches 1.20 V, and the photoelectric conversion efficiency exceeds 21%. Related research results were published in "Advanced Energy Materials" (Advanced Energy Materials, 2020, DOI: 10.1002 / aenm.202000197).
This work provides new ideas and understanding for the passivation of ammonium salts, and provides guidance for the further improvement of the efficiency of perovskite solar cells.
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