Hybrid halide perovskites are currently under intense investigation due to their potential applications in optoelectronics and solar cells. Among them, MAPbI3 where MA stands for the methylammonium cation, exhibits ideal properties for solar cells. In attempt to identify new lead-free halide perovskites we have studied using ab-initio electronic structure calculations in conjunction with hybrid functionals a series of MABX3 compounds where B is a divalent cation and X is a halogen atom. Our results suggest that the compounds under study exhibit a variety of lattice constants and energy band gaps. Especially, MAGeCl3 and MAGeBr3 are susceptible to replace MAPbI3 in devices since they show comparable energy gaps. Further calculations on the mixed hybrid halide perovskites show that we can tune the values of the energy gap although no simplified pattern exists. Our results pave the way for further investigation on the use of these materials in technology relevant applications.

In this contribution, we present the synthesis and characterization of the mixed-anion halogenobismuthate(III) (CHNH)BiICl (MBIC) as an alternative lead-free perovskite-type semiconductor, and discuss its optical, electronic, and photovoltaic properties in comparison to the methylammonium bismuth iodide (CHNH)BiI (MBI) compound. The exchange of iodide with chloride during synthesis leads to the formation of an orthorhombic ABX-type crystal structure ( Cmma, No. 67) with isolated BiX octahedra and methylammonium chloride interlayers. The experimentally found optical indirect band gap of 2.25 eV is in good agreement with the calculated value of 2.50 eV derived from DFT simulations. The valence band maximum and the conduction band minimum were determined to be at -6.2 eV and -4.0 eV vs vacuum. Similar to MBI, thin films of MBIC are composed of microcrystalline platelets. Time-resolved photoluminescence measurements show electron transfer of MBIC to mesoporous TiO. The photovoltaic behavior of both compounds is compared in solar cells with the following device architecture: glass/ITO/compact TiO/mesoporous TiO/MBIC or MBI/spiro-OMeTAD/Au. Despite the zero-dimensional structure of MBIC, a maximum power conversion efficiency of 0.18% and a high fill factor of almost 60% were obtained with this material as absorber layer. When stored under inert conditions, these solar cells show an excellent long-term stability over the investigated period of more than 700 days.

Halide perovskites are currently under intense investigation due to their potential applications in optoelectronics and solar cells. Among them several crystallize in low symmetry lattice structures like trigonal, hexagonal, orthorhombic and monoclinic. Employing ab-initio electronic structure calculations in conjunction with generalized gradient approximation and hybrid functionals we study a series of perovskites with the formula A3B2X9 which have been grown experimentally. A stands for a monovalent cation like Cs, Rb, K or the organic methylammonium molecule (MA), B is Sb or Bi, and X is a halogen. Moreover we include in our study both the effect of spin-orbit coupling in the halide perovskites and the influence of the orientation disorder of the MA cation on the energy band gaps of these compounds. Most compounds under study exhibit absorption in or close to the optical regime and thus can find application in various optoelectronic devices. Our results pave the way for further investigation on the use of these materials in technology relevant applications.

Perovskite quantum dots (QDs) constitute a novel and rapidly developing field of nanotechnology with promising potential for optoelectronic applications. However, few perovskite materials for QDs and other nanostructures have been theoretically explored. In this study, we present a wide spectrum of different hybrid halide perovskite cuboid-like QDs with the general formula of ABX 3 with varying sizes well below the Bohr exciton radius. Density functional theory (DFT) and time-dependent DFT calculations were employed to determine their structural, electronic, and optical properties. Our calculations include both stoichiometric and nonstoichiometric QDs, and our results reveal several materials with high optical absorption and application-suitable electronic and optical gaps. Our study highlights the potential as well as the challenges and issues regarding nanostructured halide perovskite materials, laying the background for future theoretical and experimental work.

Halide perovskites consist a class of materials under intense investigation due to their potential technological applications like solar cells, optoelectronic devices, and catalysis. Recently, the cubic MABX 3 compounds have been studied using electronic band structure calculations from first principles [A. Koliogiorgos et al., Comput. Mater. Sci. 2017, 138, 92], where MA stands for the methylammonium cation, B is a divalent cation, and X a halogen. In this paper, the study in the case where Cs stands in place of the MA cation is expanded. The results suggest that the Cs-based compounds exhibit also a variety of lattice constants and energy band gaps. The calculated equilibrium lattice constants differ substantially from the experimental ones. The calculated energy gaps also show large deviations for these lattice constants. Moreover, the use of more sophisticated functionals leads to conflicting changes in the energy gap values and its effect is materials dependent. The results suggest that contrary to the MA halide perovskites, the Cs halide perovskites consist a more delicate case and there is still a long way for ab initio calculations to accurately describe their structural and electronic properties.