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The linear dichroism (LD) transition within anisotropic photonic materials displays promising prospects for applications in polarization-wavelength-selective detectors, optical switching, and optical communication. In conventional two-dimensional (2D) anisotropic materials, the LD is predominantly uniaxial over a broad spectrum of wavelengths and arises principally from the reduced symmetry of the materials. However, the LD transition behavior in crystalline 2D materials remains elusive. Here, we demonstrate the observation of a unique LD conversion phenomenon at a wavelength of 472 nm in palladium diselenide (PdSe2) using polarization-resolved absorption spectroscopy. This material exhibits prominent anisotropic responses and a high absorption ratio of α y /α x ≈ 1.11 at 364 nm, 1.15 at 532 nm, and 0.84 at 633 nm. We propose that this abnormal LD conversion behavior originates from the forceful localization rules at different parallel energy bands that exist within this material. Furthermore, the robust periodicity of Ag and B1g modes in polarization-resolved Raman spectroscopy is in good agreement with the theoretical structure symmetry analysis. This indicates the strong intrinsic LD effect in the anisotropic nature of PdSe2, which offers a macrolevel determination of crystal orientations. Such unique LD conversion features, in combination with strong LD effects, enable the air-stable PdSe2 to be a potential candidate for technological innovations in multispectral imaging, sensing, and polarization-sensitive and wavelength-controllable photoelectronic applications.

Perovskite solar cells (PSCs) are being rapidly developed at a fiery stage due to their marvelous and fast-growing power conversion efficiency (PCE). Advantages such as high PCE, solution processability, tunable band gaps, and flexibility make PSCs one of the research hot spots in the energy field. Flexible PSCs (f-PSCs) owing to high power-to-weight ratios can be promising candidates to serve as power sources in mobile energy systems, space energy systems, portable functional devices, and so on. Herein, we give a review on recent progress in f-PSCs involving flexible substrates and flexible transparent electrodes, performance enhancement by optimizing functional layers, large-scale fabrication techniques, flexibility promotion strategies, and their potential applications. Furthermore, perspectives are discussed on the future development of f-PSCs.

Flexible perovskite solar cells (f‐PSCs) have been attracting tremendous attention due to their potentially commercial prospects in flexible energy system and mobile energy system. Reducing the energy barriers and charge extraction losses at the interfaces between perovskite and charge transport layers is essential to improve both efficiency and stability of f‐PSCs. Herein, 4‐trifluoromethylphenylethylamine iodide (CF3PEAI) is introduced to form a 2D perovskite at the interface between perovskite and hole transport layer (HTL). It is found that the 2D perovskite plays a dual‐functional role in aligning energy band between perovskite and HTL and passivating the traps in the 3D perovskite, thus reducing energy loss and charge carrier recombination at the interface, facilitating the hole transfer from perovskite to the Spiro‐OMeTAD. Consequently, the photovoltaic performance of f‐PSCs is significantly improved, leading to a power conversion efficiency (PCE) of 21.1% and a certified PCE of 20.5%. Furthermore, the long‐term stability of f‐PSCs is greatly improved through the protection of 2D perovskite layer to the underlying 3D perovskite. This work provides an excellent strategy to produce efficient and stable f‐PSCs, which will accelerate their potential applications.

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