Optical and Structural Property Tuning in Physical Vapor Deposited Bismuth Halides Cs3Bi2(I1-xBrx)9 (0 ≤ x ≤ 1).

Crystalline films of lead-free all-inorganic Cs3Bi2X9 (X = Br, I) perovskites have been deposited by radio frequency (RF)-magnetron sputtering providing high-quality, single-phase films as confirmed by structural, morphological, and optical property characterization. Progressive tuning of crystal structure characteristics and optical absorbance has been achieved in mixed Br/I phases Cs3Bi2(I1-xBrx)9 (0 ≤ x ≤ 1), highlighting a shift of the band gap from about 2.0 eV for Cs3Bi2I9 to 2.64 eV for Cs3Bi2Br9. X-ray diffraction and Raman scattering allowed defining the range of alloyed compositions where single-phase compositions are found. Finally, preliminary photocatalytic activity tests on the degradation of methylene blue provided solid data indicating the future possible exploitation of Bi-based perovskite derivative materials as active photocatalysts.

Versatile vapor phase deposition approach to cesium tin bromide materials CsSnBr3, CsSn2Br5 and Cs2SnBr6.

We report on the successful application of RF-magnetron sputtering to deposit, by using a single type of target, three different materials in the form of thin films within the Cs-Sn-Br compositional range, namely, CsSnBr3, CsSn2Br5 and Cs2SnBr6. It is shown that, by playing with the deposition parameters and post-deposition treatments, it is possible to stabilize these three perovskites or perovskite related compounds by exploiting the versatility of vapor phase deposition. Full characterization in terms of crystal structure, optical properties and morphology is reported. The power of vapor phase methods in growing all-inorganic materials of interest for photovoltaic and optoelectronic applications is demonstrated here, indicating the advantageous use of sputtering for these complex materials.

Band Gap Engineering in MASnBr3 and CsSnBr3 Perovskites: Mechanistic Insights through the Application of Pressure.

Here we report on the first structural and optical high-pressure investigation of MASnBr3 (MA = [CH3NH3]+) and CsSnBr3 halide perovskites. A massive red shift of 0.4 eV for MASnBr3 and 0.2 eV for CsSnBr3 is observed within 1.3 to 1.5 GPa from absorption spectroscopy, followed by a huge blue shift of 0.3 and 0.5 eV, respectively. Synchrotron powder diffraction allowed us to correlate the upturn in the optical properties trend (onset of blue shift) with structural phase transitions from cubic to orthorhombic in MASnBr3 and from tetragonal to monoclinic for CsSnBr3. Density functional theory calculations indicate a different underlying mechanism affecting the band gap evolution with pressure, a key role of metal-halide bond lengths for CsSnBr3 and cation orientation for MASnBr3, thus showing the impact of a different A-cation on the pressure response. Finally, the investigated phases, differently from the analogous Pb-based counterparts, are robust against amorphization showing defined diffraction up to the maximum pressure used in the experiments.

Ambient condition retention of band-gap tuning in MAPbI3 induced by high pressure quenching.

In the present work, we show a successful approach to achieve stable structural and optical changes induced by pressure on bulk amounts of MAPI after pressure release. Such effects on the optical properties resemble those achieved in situ (e.g., in diamond anvil cells) but are retained and stabilized under ambient conditions thanks to a partial quenching of the high-pressure state.

Novel Physical Vapor Deposition Approach to Hybrid Perovskites: Growth of MAPbI3 Thin Films by RF-Magnetron Sputtering.

Solution-based methods represent the most widespread approach used to deposit hybrid organic-inorganic perovskite films for low-cost but efficient solar cells. However, solution-process techniques offer limited control over film morphology and crystallinity, and most importantly do not allow sequential film deposition to produce perovskite-perovskite heterostructures. Here the successful deposition of CH3NH3PbI3 (MAPI) thin films by RF-magnetron sputtering is reported, an industry-tested method to grow large area devices with precisely controlled stoichiometry. MAPI films are grown starting from a single-target made of CH3NH3I (MAI) and PbI2. Films are single-phase, with a barely detectable content of unreacted PbI2, full surface coverage and thickness ranging from less than 200 nm to more than 3 µm. Light absorption and emission properties of the deposited films are comparable to as-grown solution-processed MAPI films. The development of vapor-phase deposition methods is of interest to advance perovskite photovoltaic devices with the possibility of fabricating perovskite multijunction solar cells or multicolor bright light-emitting devices in the whole visible spectrum.