Considering the toxicity of lead ions, substituting Pb with nontoxic elements in halide perovskites, HaPs, has become one of the most significant challenges associated with these materials. Here, we report on replacing Pb with Sn and Ge, focusing on an all-inorganic HaP, CsSn_xGe_1–xBr₃, and using a multihead spray deposition setup for thin-film formation to overcome the low solubility of the precursors and improve film coverage. We find that, in this way, we can form CsSn_xGe_1–xBr₃ films up to high x values as homogeneous solid solutions; i.e., we obtain a range of compositions with one crystal structure (rather than clusters of two phases). The cubic structure of pure CsSnBr₃ is maintained up to 77 atom % Ge, with the lattice spacing decreasing with increasing Ge concentration. The optical band gap is tunable between 1.8 and 2.5 eV, from pure Sn to pure Ge HaP. Most importantly, the perovskite structural stability increases with increasing concentration of Ge, with less oxidation of both Ge and Sn to the +4 state, which can be ascribed to less octahedral tilting and stronger bonding. Electrical and electronic transport measurements show the potential of these materials as Pb-free absorbers for solar cells, particularly, given their band gap range as the top cell of a tandem photovoltaic device.

The interfaces between inorganic selective contacts and halide perovskites (HaPs) are possibly the greatest challenge for making stable and reproducible solar cells with these materials. NiO_x, an attractive hole-transport layer as it fits the electronic structure of HaPs, is highly stable and can be produced at a low cost. Furthermore, NiO_x can be fabricated via scalable and controlled physical deposition methods such as RF sputtering to facilitate the quest for scalable, solvent-free, vacuum-deposited HaP-based solar cells (PSCs). However, the interface between NiO_x and HaPs is still not well-controlled, which leads at times to a lack of stability and V_oc losses. Here, we use RF sputtering to fabricate NiO_x and then cover it with a Ni_yN layer without breaking vacuum. The Ni_yN layer protects NiO_x doubly during PSC production. Firstly, the Ni_yN layer protects NiO_x from Ni³⁺ species being reduced to Ni²⁺ by Ar plasma, thus maintaining NiO_x conductivity. Secondly, it passivates the interface between NiO_x and the HaPs, retaining PSC stability over time. This double effect improves PSC efficiency from an average of 16.5% with a 17.4% record cell to a 19% average with a 19.8% record cell and increases the device stability.

Two-dimensional (2D) halide perovskites, HaPs, can provide chemical stability to three-dimensional (3D) HaP surfaces, protecting them from exposure to ambient species and from reacting with contacting layers. Both actions occur with 2D HaPs, with the general stoichiometry R₂PbI₄ (R: long or bulky organic amine) covering the 3D ones. Adding such covering films can also boost power conversion efficiencies of photovoltaic cells by passivating surface/interface trap states. For maximum benefit, we need conformal ultrathin and phase-pure (n = 1) 2D layers to enable efficient tunneling of photogenerated charge carriers through the 2D film barrier. Conformal coverage of ultrathin (<10 nm) R₂PbI₄ layers on 3D perovskites is challenging with spin coating; even more so is its upscaling for larger-area devices. We report on vapor-phase cation exchange of the 3D surface with the R₂PbI₄ molecules and real-time in situ growth monitoring by photoluminescence (PL) to determine limits for forming ultrathin 2D layers. We characterize the 2D growth stages, following the changing PL intensity-time profiles, by combining structural, optical, morphological, and compositional characterizations. Moreover, from quantitative X-ray photoelectron spectroscopy (XPS) analysis on 2D/3D bilayer films, we estimate the smallest width of a 2D cover that we can grow to be <5 nm, roughly the limit for efficient tunneling through a (semi)conjugated organic barrier. We also find that, besides protecting the 3D against ambient humidity-induced degradation, the ultrathin 2D-on-3D film also aids self-repair following photodamage.

Methods for fast quantification of XPS data of a Cu _x Ni _{1− x} O _y combinatorial material library were evaluated in a step towards high-throughput analysis.

A study conducted to investigate the fabrication of organic solar cells based on PC61BM:PCPDTBT using the Physical Vapor Deposition (PVD) method. The research carries out a number of analyses for structural evaluations (XRD and ESEM), compositional change (XPS and FTIR), and functional assessment (absorption and I-V testing), with the goal of understanding the materials' properties, their behavior during deposition and the resulting characteristics of the fabricated solar cells. While demonstrating promise, the PVD method faces challenges in the maintenance of electrical attributes during vaporization, and the need for further optimization. The findings highlight both the advantages and limitations of the method and point the way toward achieving optimal outcomes in the manufacture of organic solar cells using PVD. The main scientific contribution of this manuscript lies in the application of the PVD method for fabricating PCPDTBT. The final device features a working solar cell device made of the materials discussed above with Cell size of 0.0026 m m 2 , cell efficiency of about 0.18 % and thickness of 309 nm-400nm. These results showcasing the possibility of building and fabricating organic cells with the PVD method.