Air-stable caesium tin iodide double perovskite (Cs2SnI6) thin films have been fabricatedviaaerosol-assisted chemical vapour deposition (AACVD).

Near-ambient-pressure X-ray photoelectron spectroscopy enables the study of the reaction of in situ-prepared methylammonium lead iodide (MAPI) perovskite at realistic water vapour pressures for the first time. We show that MAPI decomposes directly to PbI, HI and NH without formation of methylammonium iodide, allowing us to distinguish between alternative mechanisms for the atmospheric degradation reaction.

Perovskite solar cells (PSCs) based on organic–inorganic hybrid perovskites containing a small fraction of substituted alkali-metal cations have shown remarkable performance and stability. However, the role of these cations is unclear. The thermal- and moisture-induced degradation of FA1–x Cs x PbI3 and (FA1–x Cs x )1–y Rb y PbI3 (where FA represents formamidinium, x, y = 0.1, 0.05) is investigated using in situ photoelectron spectroscopy (PES). Both compositions exhibit superior moisture stability compared with methylammonium lead iodide under 9 mbar of water vapor. Ga Kα hard X-ray PES is used to investigate the composition of the perovskites at depths up to 45 nm into the surface. This allows more accurate quantification of the alkali-metal distribution than is possible using conventional X-ray PES. The addition of RbI results in a fairly homogeneous distribution of both Cs+ and Rb+ in the surface layers (in contrast to surface Cs depletion seen in its absence), together with a marked reduction in surface iodide vacancies. Overall, RbI is found to play a critical role in increasing the thermal stability of FA1–x Cs x PbI3 by providing a source of I– that fills iodine vacancy sites in the perovskite lattice, while Rb+ is not substantially incorporated into the perovskite. We suggest that the concomitant increase in ion migration barriers in the surface layers is key to improved PSC performance and long-lasting stability.

When hydroxyapatite nanoparticles are included in the mesoporous scaffold for perovskite solar cells they not only improve the power conversion efficiency but sequester released Pb if broken cells are immersed in water.

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A one-step laser process is applied to fabricate mesoporous and compact TiO2 films in 1 min for perovskite solar cells.

The synthesis and characterization of TiO 2 beads and the use of them in the photoanodes of all-plastic flexible dye-sensitized solar cells (FDSCs) are reported. Pure anatase TiO 2 beads having different sizes and characteristics were first made using a novel two-step chemical method under different conditions. Photoanodes consisting of the beads as scattering layers were then fabricated. The use of beads largely enhances the dye loading and gives highly effective light scattering, leading to improved light absorbance. The resulting cells were evaluated for the electron diffusion time, electron lifetime, charge collection efficiency, incident photon-to-electron conversion efficiency, electron injection efficiency, and IV characteristics. The pure anatase TiO 2 beads, having low oxygen vacancy concentrations and directional attached grains, lead to more photoelectrons and enhance the electron diffusion, giving very short diffusion times. We have demonstrated for the first time that the use of beads, having diameters ranging from 250 to 750 nm, enhances the light-to-electricity conversion efficiency of FDSCs having plastic substrates by as much as 28%. The cell conversion efficiency is also enhanced from 4.3 to 5.5%.

Ambient-air-stable methylammonium lead iodide (MAPI) perovskite thin films have been fabricated via one-step aerosol-assisted chemical vapor deposition (AACVD) from a pseudohalide Pb(SCN) 2 precursor. We compare both the bulk and surface properties of the perovskite films grown using AACVD with those made by the widely used spin-coating method. Films with larger grain sizes and much better stability in ambient air can be obtained by AACVD. By addition of excess MAI to the precursor solution, MAPI films with negligible PbI 2 impurities, as determined by X-ray diffraction, are obtained. The AACVD-grown MAPI films retain high phase purity with limited PbI 2 formation after aging in air for approximately one month. The films exhibit an optical bandgap energy of ca. 1.55 eV and the expected nominal bulk stoichiometry (within error). In addition to probing bulk properties, we utilize X-ray photoelectron spectroscopy (XPS) to scrutinize the surface characteristics in detail. We find that the use of excess MAI results in formation of neutral CH 3 NH 2 molecules at the surface. With aging time in air, the concentrations of iodine and nitrogen drop with respect to that of lead, but these changes are less severe in the AACVD-grown films compared to the counterparts made by spin-coating. Near-ambient pressure XPS is utilized to examine the surface stability of AACVD-grown films on exposure to 9 mbar H 2 O vapor. The formation of CH 3 NH 2 molecules at the surface is observed, and the MAPI phase remains largely intact. The CH 3 NH 2 molecules may passivate the surfaces and protect MAPI from degradation, providing a rationale for the observed stability of MAPI films fabricated from Pb(SCN) 2 with excess MAI.