Juan Felipe Montoya

Self-Functionalization Behind a Solution-Processed NiOx Film Used As Hole Transporting Layer for Efficient Perovskite Solar Cells

Fabrication of solution-processed perovskite solar cells (PSCs) requires the deposition of high quality films from precursor inks. Frequently, buffer layers of PSCs are formed from dispersions of metal oxide nanoparticles (NPs). Therefore, the development of trustable methods for the preparation of stable colloidal NPs dispersions is crucial. In this work, a novel approach to form very compact semiconducting buffer layers with suitable optoelectronic properties is presented through a self-functionalization process of the nanocrystalline particles by their own amorphous phase and without adding any other inorganic or organic functionalization component or surfactant. Such interconnecting amorphous phase composed by residual nitrate, hydroxide, and sodium ions, proved to be fundamental to reach stable colloidal dispersions and contribute to assemble the separate crystalline nickel oxide NPs in the final film, resulting in a very homogeneous and compact layer. A proposed mechanism behind the great stabilization of the nanoparticles is exposed. At the end, the self-functionalized nickel oxide layer exhibited high optoelectronic properties enabling perovskite p-i-n solar cells as efficient as 16.6% demonstrating the pertinence of the presented strategy to obtain high quality buffer layers processed in solution at room temperature.

Degradacion de naranja de metilo en un nuevo fotorreactor solar de placa plana con superficie corrugada

Methyl Orange degradation (MO) by heterogeneous photocatalysis using titanium dioxide Degussa P-25 and solar radiation in a photoreactor of corrugated plates was studied. Initial MO concentration, TiO2 amount and the catalyst disposition were used as experimental variables. MO degradation reached 99% and it adjusted to the model of Langmuir - Hinshelwood. The reaction followed an apparent firstorder kinetics with respect to the MO and it showed an increase in the rate constant when increasing the suspended catalyst amount and diminishing the initial MO concentration.

Catalytic role of bridging oxygens in TiO2 liquid phase photocatalytic reactions: analysis of H216O photooxidation on labeled Ti18O2

Experiments of photocatalytic oxidation of H216O with a suspended oxygen-isotope labelled Ti18O2 photocatalyst are presented here for the first time. The photo-induced evolution of 18O16O demonstrates that bridging surface oxygens (>18Obr2−) behave as real catalytic species of the global water splitting photocatalytic reaction (2H2O + 4h+ → O2(g)↑ + 4H+). The experimental results are interpreted according to a previously developed water redox photooxidation (WRP) mechanism (Salvador, P. Prog. Surf. Sci. 2011, 86, 41–58), opening a new mechanistic pathway that involves the participation of terminal >Obr2− bridging oxygens as real photocatalytic species. In the primary step, one-fold coordinated −18Obr˙− radicals are generated from the direct photooxidation of >18Obr2− oxygens with valence band holes (>18Obr2− + h+ → −18Obr˙−). In the second step, a couple of adjacent −18Obr˙− radicals chemically react, giving rise to peroxo species (218Obr˙− → 18O22−), which are further photooxidized with photogenerated valence band holes, initially leading to 18O2(g) evolution according to the global photoreaction 18O22− + 4h+ → 2V[>18Obr2−] + 18O2(g)↑. Terminal oxygen vacancies (V[>18Obr2−]) become further healed via dissociative adsorption of H216O water molecules (2V[>18Obr2−] + 2H216O → 2(>16Obr2−) + 2H+), in such a way that >18Obr2− bridging ions are progressively substituted by >16Obr2− and the initially evolved 18O2(g) is further replaced by 16,18O2(g) and finally by 16O2(g).

Simultaneous Top and Bottom Perovskite Interface Engineering by Fullerene Surface Modification of Titanium Dioxide as Electron Transport Layer

Optimization of the interface between the electron transport layer (ETL) and the hybrid perovskite is crucial to achieve high-performance perovskite solar cell (PSC) devices. Fullerene-based compounds have attracted attention as modifiers on the surface properties of TiO2, the archetypal ETL in regular n-i-p PSCs. However, the partial solubility of fullerenes in the aprotic solvents used for perovskite deposition hinders its application to low-temperature solution-processed PSCs. In this work, we introduce a new method for fullerene modification of TiO2 layers derived from nanoparticles (NPs) inks. Atomic force microscopy characterization reveals that the resulting ETL is a network of TiO2-NPs interconnected by fullerenes. Interestingly, this surface modification enhances the bottom interface of the perovskite by improving the charge transfer as well as the top perovskite interface by reducing surface trap states enhancing the contact with the p-type buffer layer. As a result, rigid PSCs reached a 17.2% power conversion efficiency (PCE), while flexible PSCs exhibited a remarkable stabilized PCE of 12.2% demonstrating the potential application of this approach for further scale-up of PSC devices.

Study of the Crystallization of Metal Halide Perovskites Containing Additives via Differential Scanning Calorimetry

Control of the crystallization and morphology has been one of the major challenges in the design and fabrication of perovskite thin films. Recently, additives of different nature have been used to improve the crystallization and the quality of perovskite films. In this work, we study in detail the role of water (H2O), 1,8-diiodooctane (DIO), and dimethylsulfoxide (DMSO) as additives in the precursor solution of the CH3NH3PbI3−xClx perovskite. Differential scanning calorimetry analysis revealed the thermal transitions for the crystallization of CH3NH3PbI3−xClx perovskite depending on the chemical nature and physical properties of the additive. Information from thermograms enabled us to find optimal annealing ramps for each additive. We found that DIO produced changes mainly due to the interaction of this additive with the precursor salts in solution, while H2O due to its different boiling point compared to the DMF solvent. DMSO dramatically modified the thermal transitions to higher temperatures; however, high quality films were obtained only when the solvent engineering method is used.