Formamidinium lead iodide (FAPbI₃)-based perovskite solar cells have gained immense popularity over the last few years within the perovskite research community due to their incredible opto-electronic properties and the record power conversion efficiencies (PCEs) achieved by the solar cells. However, FAPbI₃ is vulnerable to phase transitions even at room temperature, which cause structural instability and eventual device failure during operation. We performed post-treatment of the FAPbI₃ surface with octyl ammonium iodide (OAI) in order to stabilize the active phase and preserve the crystal structure of FAPbI₃. The formation of a 2D perovskite at the interface depends on the stoichiometry of the precursor. By optimizing the precursor stoichiometry and the concentration of OAI, we observe a synergistic effect, which results in improved power conversion efficiencies, reaching the best values of 22% on a glass substrate. Using physical and detailed optical analysis, we verify the presence of the 2D layer on the top of the 3D surface of the perovskite film.

The aim of this study was to determine the electronic properties of as-deposited ALD-grown Ge-doped zinc oxide thin films annealed at 523 K or 673 K. SEM, EDS, and ellipsometry measurements confirmed that the Ge-doped zinc oxide films with a thickness of around 100 nm and uniform composition were successfully obtained. GI-XRD measurements did not reveal phases other than the expected Wurtzite structure of the ZnO. The electronic properties, i.e., conductivity, charge carrier concentration, and mobility of the films, were evaluated using Hall effect measurements and explained based on corresponding XPS measurements. This work supports the theory that oxygen vacancies act as electron donors and contribute to the intrinsic n-type conductivity of ZnO. Also, it is shown that the effect of oxygen vacancies on the electronic properties of the material is stronger than the effect introduced by Ge doping.

In this work, we report on the fabrication of ZnO thin films doped with Ge via the ALD method. With an optimized amount of Ge doping, there was an improvement in the conductivity of the films owing to an increase in the carrier concentration. The optical properties of the films doped with Ge show improved transmittance and reduced reflectance, making them more attractive for opto-electronic applications. The band gap of the films exhibits a blue shift with Ge doping due to the Burstein–Moss effect. The variations in the band gap and the work function of ZnO depend strongly on the carrier density of the films. From the surface studies carried out using XPS, we could confirm that Ge replaces some of the Zn in the wurtzite structure. In the films containing Ge, the concentration of oxygen vacancies is also high, which is somehow related to the poor electrical properties of the films at higher Ge concentrations.