Impact of light illumination on the surface structure of two-dimensional Ruddlesden–Popper perovskite in the fabrication process

Abstract

Two-dimensional Ruddlesden–Popper (2DRP) perovskites are promising owing to their excellent environmental stability and competitive efficiency. During the fabrication process, 2DRP perovskites were often unintentionally exposed to light in the laboratory. However, the influence of light illumination on the surface structure of 2DRP during fabrication is unclear. Herein, the photodegradation of 2DRP perovskite (phenethylammonium lead iodide, PEA2PbI4) is comprehensively investigated using X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, and photoluminescence spectroscopy. We observed that only high-energy light, including that from a blue laser, air mass 1.5G, and notably, the daily used fluorescent lamp (FL) in the laboratory, significantly degraded PEA2PbI4. However, the red laser and ultraviolet-filtered FL, which had low energies, did not cause photodegradation. From this systematic study, we can explain the discrepancies in the surface morphologies previously studied. For instance, randomly oriented nanorod or rough surface of PEA2PbI4 mostly stems from photodegradation. We observed that photodegradation occurred more strongly when the films were illuminated during annealing than when they were illuminated after all fabrication processes were completed. We suggest that this difference stems from the completeness of the structure and the photodegraded PbI2 passivation effect. Our study provides two key guidelines for the fabrication of PEA2PbI4 films. The daily-use FL in the laboratory must be avoided for high-quality samples, and dark conditions are highly recommended, at least during the annealing process.

Enhancing photostability of 2D Ruddlesden–Popper perovskite via molecular acceptor passivation of metallic lead defects

“…6,[46][47][48] Blue laser irradiation (k ¼ 405 nm, intensity ¼ 50 mW cm À2 ) was used to degrade the prepared PEA 2 PbI 4 films since a higher photon energy causes more significant degradation. 28,29 We also carefully controlled the irradiation time and dose of x-ray and UV sources to prevent undesired degradation of the PEA 2 PbI 4 samples during measurements (supplementary material Sec. 3).…”

“…26,27 However, ironically, photostability has become a major topic of discussion among researchers in the 2D perovskite research field, as it is a significant challenge to their application in optoelectronic devices. [28][29][30][31][32][33] For example, the daily used fluorescent lamps, which emit also high-energy photons at extremely low intensities, can rapidly degrade the surface structure of 2D RP perovskites. 29 In many reports, it has been also revealed that the high-energy light irradiation on perovskites can disrupt crystalline structures, leading to undercoordinated Pb states that impede carrier transport and cause substantial loss of photoluminescence (PL).…”

“…[28][29][30][31][32][33] For example, the daily used fluorescent lamps, which emit also high-energy photons at extremely low intensities, can rapidly degrade the surface structure of 2D RP perovskites. 29 In many reports, it has been also revealed that the high-energy light irradiation on perovskites can disrupt crystalline structures, leading to undercoordinated Pb states that impede carrier transport and cause substantial loss of photoluminescence (PL). [13][14][15]28,29,[34][35][36] These photodegradation processes produce metallic Pb 0 defects, which act as non-radiative recombination centers and accelerate undesired chemical reactions owing to their high reactivity.…”

“…29 In many reports, it has been also revealed that the high-energy light irradiation on perovskites can disrupt crystalline structures, leading to undercoordinated Pb states that impede carrier transport and cause substantial loss of photoluminescence (PL). [13][14][15]28,29,[34][35][36] These photodegradation processes produce metallic Pb 0 defects, which act as non-radiative recombination centers and accelerate undesired chemical reactions owing to their high reactivity. [34][35][36][37][38][39] Hence, to achieve improved photostability, it is imperative to develop effective passivation or suppression techniques to prevent the formation of metallic Pb 0 defects.…”