This paper presents the synthesis of the organic-inorganic hybrid perovskite, CH3NH3PbI3, doped in the Pb(2+) position with Sn(2+), Sr(2+), Cd(2+) and Ca(2+). The incorporation of the dopants into the crystalline structure was analysed, observing how the characteristics of the dopant affected properties such as the crystalline phase, emission and optical properties. XRD showed how doping with Sn(2+), Sr(2+) and Cd(2+) did not modify the normal tetragonal phase. When doping with Ca(2+), the cubic phase was obtained. Moreover, DR-UV-Vis spectroscopy showed how the band gap decreased with the dopants, the values following the trend Sr(2+) < Cd(2+) < Ca(2+) < CH3NH3PbI3 ≈ Sn(2+). The biggest decrease was generated by Sr(2+), which reduced the CH3NH3PbI3 value by 4.5%. In turn, cathodoluminescence (CL) measurements confirmed the band gap obtained. Periodic-DFT calculations were performed to understand the experimental structures. The DOS analysis confirmed the experimental results obtained using UV-Vis spectroscopy, with the values calculated following the trend Sn(2+) ≈ Pb(2+) > Cd(2+) > Sr(2+) for the tetragonal structure and Pb(2+) > Ca(2+) for the cubic phase. The electron localization function (ELF) analysis showed similar electron localizations for undoped and Sn(2+)-doped tetragonal structures, which were different from those doped with Sr(2+) and Cd(2+). Furthermore, when Cd(2+) was incorporated, the Cd-I interaction was strengthened. For Ca(2+) doping, the Ca-I interaction had a greater ionic nature than Cd-I. Finally, an analysis based on the non-covalent interaction (NCI) index is presented to determine the weak-type interactions of the CH3NH3 groups with the dopant and I atoms. To our knowledge, this kind of analysis with these hybrid systems has not been performed previously.

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Solar cells, light emitting diodes, and X-ray detectors based on perovskite materials often incorporate gold electrodes, either in direct or indirect contact with the perovskite compound. Chemical interactions between active layers and contacts deteriorate the operation and induce degradation, being the identification of the chemical nature of such interfacial structures an open question. Chemical reactivity of gold in contact with the perovskite semiconductor leads to reversible formation of oxidized gold halide species and explains the generation of halide vacancies in the vicinity of the interface.Electrical biasing induces contact reaction and produces modifications of the current level by favoring the ability of perovskite/Au interfaces to inject electronic carriers. The current injection increment does not depend on the halogen source used, either extrinsically by iodine vapor sublimation of Au electrodes, or intrinsically by bias-driven migration of bromide ions. In addition, the formation of a dipole-like structure at the reacted electrode that lowers the potential barrier for electronic carriers is confirmed. These findings highlight adequate selection of the external contacts and suggest the need for a deeper understanding of contact reactivity as it dominates the operation characteristics, rather than being governed by the bulk transport properties of the charge carriers, either electronic or ionic.conversion in the near future. In addition to photovoltaic applications, perovskitebased materials are being explored as sensitive layers for high-energy radiation detectors and imaging devices for medical diagnostics. [2] These detection technologies rely upon the ability of perovskite compounds of absorbing high-energy photons and convert their energy into electronic carriers that are finally collected at the outer contacts. For soft X-ray photons (<10 keV), absorbing layer thickness of tens of micrometers suffices to stop the radiation. But hard X-ray radiation (10-50 keV) possesses much longer penetration length (≈100 µm) in compounds as methylammonium lead iodide or bromide (MAPbI 3 and MAPbBr 3 ). [3] Hence, relatively thick layers (0.1-1 mm) need to be employed to achieve sufficient electrical signal. Despite the large electronic carrier mobility and mobility-lifetime product, [4,5] such thick absorbing layers should be externally biased in order to increase the detector responsivity. Electrical fields as high as ≈0.1-1 V µm −1 are commonly needed for poly-crystalline perovskite deposits incorporated into X-ray detectors. [3,5] Large field strength requirements are in some amount lowered when devising single-crystal approaches for X-ray detection using perovskite materials. [4,6] In any case, it is widely recognized that the application of an external bias promotes the displacement and interfacial built-up of intrinsic mobile ions. [7,8] Ion accumulation finally shields the electrical field within the absorbing layer bulk, reducing as a consequence the detector sensitivity. The applicability of perovs...

Methylammonium Lead Iodide (CH 3 NH 3 PbI 3 ) is the archetypical active component of perovskite solar cells, which stand out due to their impressive photovoltaic performance. A major drawback of CH 3 NH 3 PbI 3 is its rapid degradation in humid environments.In this work, we fabricate CH 3 NH 3 PbI 3 films and devices by solvent engineering in N 2 and in ambient conditions with different humidities. Their aging and degradation is monitored by optical absorption and impedance spectroscopy measurements under monochromatic illumination with two different wavelengths. Aged devices show a substantial difference between the recombination rate under red and blue light illumination, attributed to enhancement of local recombination routes upon aging. Interestingly, we observe that devices prepared at higher humidity resist better the aging. We explain this by the presence of coordinating water in the films, as detected by XPS measurements. Hence, small amounts of water in the perovskite structure proves to have a beneficial effect against degradation in humid environments.

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Methodology to prepare highly stable and improved nanofluids controlling the nanomaterial morphology.

This paper presents the synthesis of organic-inorganic hybrid perovskite CH3NH3Pb1-xCdxI3. The effect of incorporating Cd(2+) or Pb(2+) on the stability of the perovskite structure was analysed from a theoretical and experimental viewpoint. The XRD results showed that the tetragonal perovskite structure was formed for x values of up to 0.5, which seems to indicate that the presence of a considerable amount of Pb(2+) is necessary to stabilise the structure. In turn, UV-Vis spectroscopy showed how the presence of Cd(2+) led to a reduction in the optical band gap of the perovskite structure of up to 9% for CH3NH3Pb0.5Cd0.5I3 with regard to the MAPbI3 structure. Moreover, periodic-DFT calculations were performed to understand the effect of the increased concentration of Cd on the structural and electronic properties of MAPbI3 perovskites. The analysis of both the ELF and the non-covalent interaction (NCI) index show the important role played by the Pb(2+) ions in stabilizing this kind of hybrid perovskite structures. Finally, the DOS analysis confirmed the experimental results obtained using UV-Vis spectroscopy. The theoretical band gap values decreased as the concentration of Cd increased.