The presence of defects formed during the growth and crystallization of perovskite films is a limiting factor to achieve high efficiency and stability in perovskite solar cells. Here, we present a robust route to passivate bulk and surface defects in perovskite films by using an amino-functionalized BODIPY fluorophore. The addition of amino-BODIPY into the prototype methyl ammonium lead iodide (MAPbI₃) perovskite solution significantly altered the nanomorphology of the perovskite film and alleviated the defect formation leading to efficiency enhancement and prolonged stability of perovskite solar cells with a regular structure. Similar results were obtained when using the BODIPY fluorophore in chlorobenzene (CB)-based antisolvent treatment of spin-coated perovskite films in inverted perovskite solar cells. In addition, reduction in the electron extraction barrier was evidenced. Our approach represents a universal passivation methodology for boosting the efficiency and stability in both regular and inverted perovskite solar cells.

Titania (TiO₂) is a key material used as an electron transport in dye-sensitized and halide perovskite solar cells due to its intrinsic n-type conductivity, visible transparency, low-toxicity, and abundance. Moreover, it exhibits pronounced photocatalytic properties in the ultra-violet part of the solar spectrum. However, its wide bandgap (around 3.2 eV) reduces its photocatalytic activity in the visible wavelengths’ region and electron transport ability. One of the most efficient strategies to simultaneously decrease its bandgap value and increase its n-type conductivity is doping with appropriate elements. Here, we have investigated using the density functional theory (DFT), as well as the influence of chromium (Cr), molybdenum (Mo), and tungsten (W) doping on the structural, electronic, and optical properties of TiO₂. We find that doping with group 6 elements positively impacts the above-mentioned properties and should be considered an appropriate method for photocatalystic applications. In addition to the pronounced reduction in the bandgap values, we also predict the formation of energy states inside the forbidden gap, in all the cases. These states are highly desirable for photocatalytic applications as they induce low energy transitions, thus increasing the oxide’s absorption within the visible. Still, they can be detrimental to solar cells’ performance, as they constitute trap sites for photogenerated charge carriers.

The increasing demand for efficient sensing devices with facile low-cost fabrication has attracted a lot of scientific research effort in the recent years. In particular, the scientific community aims to develop new candidate materials suitable for energy-related devices, such as sensors and photovoltaics or clean energy applications such as hydrogen production. One of the most prominent methods to improve materials functionality and performance is doping key device component(s). This paper aims to examine in detail, both from a theoretical and an experimental point of view, the effect of halogen doping on the properties of tin dioxide (SnO₂) and provide a deeper understanding on the atomic scale mechanisms with respect to their potential applications in sensors. Density Functional Theory (DFT) calculations are used to examine the defect processes, the electronic structure and the thermodynamical properties of halogen-doped SnO₂. Calculations show that halogen doping reduces the oxide bandgap by creating gap states which agree well with our experimental data. The crystallinity and morphology of the samples is also altered. The synergy of these effects results in a significant improvement of the gas-sensing response. This work demonstrates for the first time a complete theoretical and experimental characterization of halogen-doped SnO₂ and investigates the possible responsible mechanisms. Our results illustrate that halogen doping is a low-cost method that significantly enhances the room temperature response of SnO₂.

Titanium dioxide (TiO₂) is one of the most used oxides in renewable energy applications, such as hydrogen production, photovoltaics, and light-emitting diodes. To further improve the efficiency of the devices, doping strategies are used to modify their fundamental properties. Here, we used density functional theory (DFT) simulations to explore the effect of all the halogen dopants on the structural, electronic, and optical properties of TiO₂. We investigated both the interstitial and the oxygen substitutional positions, and for the optimized structures, we used hybrid DFT calculations to predict the electronic and optical properties. In all cases, we found that halogen dopants reduce the bandgap of the pristine TiO₂ while gap states also arise. The halogen dopants constitute a single acceptor when they occupy interstitial sites, while when they are inserted in oxygen sites, they act as donors. This can be established by the states that form above the valence band. It is proposed that these states contribute to the significant changes in the optical and electronic properties of TiO₂ and can be beneficial to the photovoltaic and photocatalytic applications of TiO₂. Importantly, the iodine doping of TiO₂ significantly reduces the bandgap of TiO₂ while increasing its dielectric constant, making it suitable for light-harvesting applications.

Defect centers in diamond have attracted considerable attention for the development of emerging quantum technologies, for example, quantum sensors and spin qubits. Nitrogen vacancy (NV) is the most well-studied and utilized defect; however, its relatively high zero phonon line (ZPL) is responsible for optical losses and limiting efficiency. Here, we focus on the halogen doping in diamond, employing the strongly constrained and appropriately normed meta-generalized gradient approximation functional to investigate the thermodynamic and electronic properties of these defects. We analyzed all stable charge states at their lowest energy spin state and identified qubit candidates with paramagnetic ground states and optically addressable transitions, suitable for quantum applications. We focus on the fluorine substitutional defect at negative charge (FC−1), which we found as a promising spin-defect that has not been extensively investigated before. We predict that it has a triplet ground state and a ZPL much lower compared to the NV center that falls into the desired telecommunication range. To describe its qubit operation protocol, we calculate the zero-field splitting and the hyperfine tensors. The present findings suggest that Fc has very promising properties and could be a viable alternative to traditional qubits in diamond.