Improvement of Colloidal Characteristics in a Precursor Solution by a PbI2-(DMSO)2 Complex for Efficient Nonstoichiometrically Prepared CsPbI2.8Br0.2 Perovskite Solar Cells

Multifunctional Heterocyclic-Based Spacer Cation for Efficient and Stable 2D/3D Perovskite Solar Cells

Two-dimensional/three-dimensional (2D/3D) Ruddlesden-Popper perovskite materials have shown the enormous potential to achieve both efficient and stable photovoltaic devices for commercial applications. Unfortunately, the single function of spacer cations limits their further improvements in efficiency to reach values as high as those of 3D perovskites. Herein, we developed a new-type multifunctional heterocyclic-based spacer cation of 2-(methylthio)-4,5-dihydro-1H-imidazole (MTIm⁺) to achieve a synchronous improvement of efficiency and stability for 2D/3D perovskite solar cells (PSCs). Owing to the presence of special chemical groups (imidazole and methylthio), strong interactions have been found between MTIm⁺ and the 3D perovskite component, leading to an excellent passivation effect. More important, at the initial stage of crystallization, uniform nucleation distribution would be generated around the spacer cation, which is helpful for improved crystallinity and reduced growth defects. The smaller layer space compared to that of cations based on aromatic hydrocarbons caused effective carrier transfer between inorganic layers in 2D/3D perovskites. As a result, the 2D/3D (n = 30) PSCs based on MTIm exhibit a champion PCE up to 21.25% with a high V_oc of 1.14 V. Besides, the 2D/3D perovskite devices have realized dramatically enhanced humidity and thermal stability, maintaining 94% of the starting PCE enduring aging at about 50% RH for 2880 h and at 85 °C for 360 h, respectively. We believe that it would provide a significant strategy to further promote the photovoltaic performances and the long-term stability of 2D/3D perovskite devices toward future practical applications.

Highly Stable Thin Films Based on Novel Hybrid 1D (PRSH)PbX3 Pseudo-Perovskites

In this study, the structure and morphology, as well as time, ultraviolet radiation, and humidity stability of thin films based on newly developed 1D (PRSH)PbX₃ (X = Br, I) pseudo-perovskite materials, containing 1D chains of face-sharing haloplumbate octahedra, are investigated. All films are strongly crystalline already at room temperature, and annealing does not promote further crystallization or film reorganization. The film microstructure is found to be strongly influenced by the anion type and, to a lesser extent, by the DMF/DMSO solvent volume ratio used during film deposition by spin-coating. Comparison of specular X-ray diffraction and complementary grazing incidence X-ray diffraction analysis indicates that the use of DMF/DMSO mixed solvents promotes the strengthening of a dominant 100 or 210 texturing, as compared the case of pure DMF, and that the haloplumbate chains always lie in a plane parallel to the substrate. Under specific DMF/DMSO solvent volume ratios, the prepared films are found to be highly stable in time (up to seven months under fluxing N₂ and in the dark) and to highly moist conditions (up to 25 days at 78% relative humidity). Furthermore, for representative (PRSH)PbX₃ films, resistance against ultraviolet exposure (λ = 380 nm) is investigated, showing complete stability after irradiation for up to 15 h at a power density of 600 mW/cm². These results make such thin films interesting for highly stable perovskite-based (opto)electronic devices.