Butanediammonium Salt Additives for Increasing Functional and Operando Stability of Light-Harvesting Materials in Perovskite Solar Cells

Organic diammonium cations are a promising component of both layered (2D) and conventional (3D) hybrid halide perovskites in terms of increasing the stability of perovskite solar cells (PSCs). We investigated the crystallization ability of phase-pure 2D perovskites based on 1,4-butanediammonium iodide (BDAI2) with the layer thicknesses n = 1, 2, 3 and, for the first time, revealed the presence of a persistent barrier to obtain BDA-based layered compounds with n > 1. Secondly, we introduced BDAI2 salt into 3D lead–iodide perovskites with different cation compositions and discovered a threshold-like nonmonotonic dependence of the perovskite microstructure, optoelectronic properties, and device performance on the amount of diammonium additive. The value of the threshold amount of BDAI2 was found to be ≤1%, below which bulk passivation plays the positive effect on charge carrier lifetimes, fraction of radiative recombination, and PSCs power conversion efficiencies (PCE). In contrast, the presence of any amount of diammonium salt leads to the sufficient enhancement of the photothermal stability of perovskite materials and devices, compared to the reference samples. The performance of all the passivated devices remained within the range of 50 to 80% of the initial PCE after 400 h of continuous 1 sun irradiation with a stabilized temperature of 65 °C, while the performance of the control devices deteriorated after 170 h of the experiment

New Insight into the Formation of Hybrid Perovskite Nanowires via Structure Directing Adducts

We report a facile preparation approach of MAPbBr(3), MAPbCl(3), or FAPbBr(3) (where MA = CH3NH3+ and FA = CH(NH2)(2)(+)) perovskite nanowires via sequential synthesis of MAPbI(3) and FAPbI(3) nanowires with chemically controlled composition and morphologies followed by an exchange of halide anions. The nanowires formation sequence includes intermediate phases such as MAI-PbI2-DMF and FAIPbIrDMF (DMF = dimethylformamide) acting as structure directing agent. The 1D shape of the adduct is preserved during the conversion to perovskite. The adducts play the role of key precursors controlling the final product morphology. Systematic investigations of the observed phase transformations and morphology features on multiple length scales revealed the effectiveness of the suggested synthetic route utilizing an original pseudomorph formation mechanism of the 1D structures to produce partly oriented films and textured layers of the nanowires via only a few experimental steps

Strategic advantages of reactive polyiodide melts for scalable perovskite photovoltaics

Despite tremendous progress in efficiency and stability, perovskite solar cells are still facing the challenge of upscaling. Here we present unique advantages of reactive polyiodide melts for solvent- and adduct-free reactionary fabrication of perovskite films exhibiting excellent quality over large areas. Our method employs a nanoscale layer of metallic Pb coated with stoichiometric amounts of CH3NH3I (MAI) or mixed CsI/MAI/NH2CHNH2I (FAI), subsequently exposed to iodine vapour. The instantly formed MAI(3(L)) or Cs(MA,FA)I-3(L) polyiodide liquid converts the Pb layer into a pure perovskite film without byproducts or unreacted components at nearly room temperature. We demonstrate highly uniform and relatively large area MAPbI(3) perovskite films, such as 100 cm(2) on glass/fluorine-doped tin oxide (FTO) and 600 cm(2) on flexible polyethylene terephthalate (PET)/indium tin oxide (ITO) substrates. As a proof-of-concept, we demonstrate solar cells with reverse scan power conversion efficiencies of 16.12% (planar MAPbI(3)), 17.18% (mesoscopic MAPbI(3)) and 16.89% (planar Cs(0.05)MA(0.2)FA(0.75)PbI(3)) in the standard FTO/c(m)-TiO2/perovskite/spiro-OMeTAD/Au architecture

Crystal Structure of DMF-Intermediate Phases Uncovers the Link Between CH3NH3PbI3 Morphology and Precursor Stoichiometry

We found for the first time a new origin of selection of perovskite crystallization pathways from DMF solutions containing MAI and PbI2 to present here a comprehensive study of a full set of essential intermediate phases determining the perovskite's morphology. For all three discovered structurally different intermediate phases forming at a given precursor ratio, we refined their crystal structures. by synchrotron X-ray radiation and investigated dynamics and phase assemblage in the course of decomposition. As a result, we revealed a clear correlation between the composition of the intermediate phases, peculiarities of their crystal structure, and the morphology of the final perovskite films. Using the DFT method we, calculated formation enthalpies of these intermediate phases and explained the preferential precipitation of DMSO-adduct rather than DMF-adduct in an antisolvent approach. This finding opens up a possibility of design-on-demand of perovskite materials using simple soft chemistry approaches

A new formation strategy of hybrid perovskites via room temperature reactive polyiodide melts

Here we introduce a new solvent-free preparation method for hybrid metal halide perovskites involving the direct reaction of metallic lead with polyiodide melts. We discovered new reactive polyiodide melts (RPMs) that can be prepared simply by adding elemental iodine to halide salts of the organic A cations of common hybrid perovskites, e.g. methylammonium iodide (MAI) and formamidinium iodide (FAI), and their corresponding bromide salts MABr and FABr. For MAI/I-2 ratios ranging from 1 : 1 to 1 : 3 they form room temperature ionic liquids containing polyiodide anions and organic counterions. We find that metallic lead can be converted within a few seconds into pure or mixed cation/anion large-grain perovskite films of high electronic quality by a reaction with the RPM. The melts can dissolve also lead derivatives, opening up a realm of opportunities for future development of self-flux growth, liquid phase epitaxy and crystallization of perovskites for solar cell applications

Crystal Structure of DMF-Intermediate Phases Uncovers the Link Between CH₃NH₃PbI₃ Morphology and Precursor Stoichiometry

We found for the first time a new origin of selection of perovskite crystallization pathways from DMF solutions containing MAI and PbI₂ to present here a comprehensive study of a full set of essential intermediate phases determining the perovskite’s morphology. For all three discovered structurally different intermediate phases forming at a given precursor ratio, we refined their crystal structures by synchrotron X-ray radiation and investigated dynamics and phase assemblage in the course of decomposition. As a result, we revealed a clear correlation between the composition of the intermediate phases, peculiarities of their crystal structure, and the morphology of the final perovskite films. Using the DFT method we calculated formation enthalpies of these intermediate phases and explained the preferential precipitation of DMSO-adduct rather than DMF-adduct in an antisolvent approach. This finding opens up a possibility of design-on-demand of perovskite materials using simple soft chemistry approaches