Orientated crystallization of FA-based perovskite via hydrogen-bonded polymer network for efficient and stable solar cells

Abstract

Incorporating mixed ion is a frequently used strategy to stabilize black-phase formamidinum lead iodide perovskite for high-efficiency solar cells. However, these devices commonly suffer from photoinduced phase segregation and humidity instability. Herein, we find that the underlying reason is that the mixed halide perovskites generally fail to grow into homogenous and high-crystalline film, due to the multiple pathways of crystal nucleation originating from various intermediate phases in the film-forming process. Therefore, we design a multifunctional fluorinated additive, which restrains the complicated intermediate phases and promotes orientated crystallization of α-phase of perovskite. Furthermore, the additives in-situ polymerize during the perovskite film formation and form a hydrogen-bonded network to stabilize α-phase. Remarkably, the polymerized additives endow a strongly hydrophobic effect to the bare perovskite film against liquid water for 5 min. The unencapsulated devices achieve 24.10% efficiency and maintain >95% of the initial efficiency for 1000 h under continuous sunlight soaking and for 2000 h at air ambient of ~50% humid, respectively.

Perovskite Films Regulation via Hydrogen‐Bonded Polymer Network for Efficient and Stable Perovskite Solar Cells

“…In pure deuterated dimethyl sulfoxide (DMSO) solution, the resonance signal of protonated ammonium in FAI was split into two at 8.99 and 8.65 ppm, respectively. This is possible due to the complicated interaction in hybrid perovskite precursors which led to different chemical environments for the two H atoms in the ammonium of FA + [9] . The peak at 7.49 ppm, corresponding to the ammonium protons in MA + , shifts downfield upon the addition of PPG‐mUPy‐APDS.…”

“…In addition, in the control perovskite film, PbI 2 crystals (white needle shapes) are distributed along the grain boundaries, which are decomposition products of perovskite after the heating procedure. [9,22,28] In contrast, the PbI 2 phase can hardly be observed in the target film. Further increasing the concentration of polymer additions, the excess polymer could crystallize and accumulate on the surface of perovskite film as shown in Supporting Information Figure 4, inhibiting carrier transportation.…”

“…Oxygen atoms in PPG-mUPy-APDS could form hydrogen bonds with charged methylamine (MA + ) and formamidine (FA + ) by NÀ H…O, and the À NH terminal groups in PPG-mUPy-APDS could form hydrogen bonds with halide ions via NÀ H…I. [9][10][11][12] Moreover, the strong interaction between C=O and Pb 2 + ions is also expected to passivate uncoordinated Pb 2 + and slow down the perovskite crystal growth. Benefitting from the multiple chemical bonding and passivation effect of supramolecular, the perovskite film demonstrated improved film quality with reduced film defects and inhibited ion migration.…”

Molecular Bridge on Buried Interface for Efficient and Stable Perovskite Solar Cells

“…Meanwhile, the RMS roughness of perovskite film is also reduced from 67.21 nm to 52.76 nm with GDA modification as evidenced from AFM characterization (Figure 3e and f). Such larger grains size with reduced GBs and reduced surface roughness are important for further suppressing charge defects and reducing interfacial series resistance for charge transfer [32] …”

“…Such larger grains size with reduced GBs and reduced surface roughness are important for further suppressing charge defects and reducing interfacial series resistance for charge transfer. [32] The perovskite films on SnO 2 layers with and without GDA modification were then subjected to X-ray diffraction (XRD) characterization. As can be seen from Figure 3g, the intensities of the main diffraction peaks of perovskite increase upon GDA modification, signifying that the GDA modification increases the crystallinity of the perovskite.…”