Advanced materials: ligand regulated excess PbI2 for efficient and stable perovskite solar cells

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Excess lead iodide (PbI2) in

can reduce the halide vacancies improve the carrier lifetime of perovskite films. Therefore perovskite solar cells (PSC) usually use excessive PbI2 as a defect passivation material to improve device efficiency. However PbI2 is a double-edged sword. Excess PbI2 is usually distributed on the upper lower surfaces of perovskite films forms energy barriers on the surface which hinder the charge longitudinal transmission. In addition the photoinduced charge aggregation of PbI2 induces the degradation of perovskite films. Therefore the reasonable control of PbI2 content distribution is very important for the device efficiency stability.

Luo Jingshan research group of Institute of optoelectronic thin film devices technology of Nankai University together with several cooperative units has developed a lig regulation technology to regulate the morphology distribution of excess PbI2 in perovskite films inspired by lig engineering to regulate the morphology of nanocrystals. A series of ligs were applied to the preparation of Perovskite Thin Films the effects of process concentration were systematically explored. The excess PbI2 was successfully distributed in the form of nanosheets at the grain boundary of Perovskite Thin Films. It not only passivates the grain boundary defects but also avoids the hindrance to the longitudinal charge transfer which effectively utilizes the advantages of PbI2 avoids its disadvantages. A series of material device characterization techniques (SEM CL mapping PL SCLC EIS etc.) have been used to verify the vertical distribution of excessive PbI2 nanosheets at the grain boundaries of perovskite films their effects on reducing the trap density prolonging the carrier lifetime of perovskite films. When cetyltrimethylammonium bromide (CTAB) is used as the lig the photoelectric conversion efficiency of the device increases from 20% to 22%. In addition due to the enhanced carrier mobility of perovskite films the hydrophobicity of surface ligs the stability of the devices under air nitrogen glove box continuous illumination is significantly improved.

researchers believe that a wide range of ligs can significantly regulate the morphology interface of various components in perovskite films which points out a new direction for the use of ligs with special functional groups to further improve the performance of perovskite devices.

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