In Situ Synthesized 2D Covalent Organic Framework Nanosheets Induce Growth of High‐Quality Perovskite Film for Efficient and Stable Solar Cells

Abstract

Poor crystallinity of perovskite and extensive defects around grain boundaries are the acknowledged hindrances to obtaining high efficiency and long-term stability for organic metal halide perovskite solar cells (PSCs). Here, a 2D covalent organic framework (2D COF) nanosheets, [(TPA) 1 (TPhT) 1 ] CN , is first in situ synthesized in a PbI 2 layer with a highly crystalline structure to precisely regulate the crystallization process of perovskite in the sequential deposition method. The existence of 2D COF nanosheets can decelerate intermolecular interdiffusion and induce perovskite crystals to grow along (110) planes with enlarged grain size. Meanwhile, 2D COF nanosheets distributed around the grain boundaries reduce the defect density and promote carriers transporting in the perovskite film. The superior properties of the perovskite film afford the champion PSC device with a power conversion efficiency of 22.04%, which is over 10% higher than the control device. Moreover, the target PSC also demonstrates outstanding long-term stability. It can maintain over 90% of its initial value after 90 days storage in ambient conditions for unencapsulated devices. This work paves a new path for regulating the crystallization process of perovskites via 2D crystalline materials.

A Universal Grain “Cage” to Suppress Halide Segregation of Mixed-Halide Inorganic Perovskite Solar Cells

“…Considering the halide segregation generally occurs in the whole perovskite layer with Br dosage over 60%, we thus use inorganic CsPbIBr 2 as a prototype to explore the effect of COFs on the phase degradation. Figure S1 shows the schematic diagram of the COF-caged perovskite grain, in which PbX 2 serves as catalyst to trigger the Schiff base reaction . During the crystallization of perovskite film, the cross-linked COFs are automatically expelled to the film surface and grain boundaries (the area between two grains within perovskite film as illustrated in Figure S2) without the interruption of crystal growth, forming a 2D network to hinder ion migration, which will be discussed in the following part.…”

A Novel Multiple‐Ring Aromatic Spacer Based 2D Ruddlesden–Popper CsPbI3Solar Cell with Record Efficiency Beyond 16%

“…The lower n trap further confirms that due to the improved quality of 1-NA-Pb film, the reduced charge carrier recombination favors charge transport. [56][57][58] Photovoltaic devices were fabricated via the structure of FTO/ TiO 2 /2D RP CsPbI 3 /Spiro-OMeTAD/MoO 3 /Ag. By using PEA-Pb and 1-NA-Pb (n = 4) perovskites as photoactive layers, the corresponding J-V characteristic curves are illustrated in Figure 5a and the performance parameters are listed in Table 1.…”

Construction of Stable Donor–Acceptor Type Covalent Organic Frameworks as Functional Platform for Effective Perovskite Solar Cell Enhancement

“…PCE is a vital parameter for solar cells, and there is no doubt that COFs have promising potential in photovoltaic applications because of their good photoelectric properties. [44][45][46][47][48] Bein and co-workers first reported the functional platform, but the PCE of COF-based devices was only 0.053%. [44] COFs could not only be used as electron or hole transport materials, but also as interlayers to enhance the PCE of perovskite solar cells.…”