Electrochemical growth of Silicon nanostructures for photovoltaic applications

Silicon is the most widely used material for current photovoltaic (PV) panel manufacturing. Next generation solar cells will be obtained by creating novel device structures, material fabrication processes and implementing new physical principles. In this regard, semiconductor nanostructures have shown their potential for achieving efficient solar energy conversion at low cost due to their particular and tunable optical properties. Nevertheless, most of the fabrication techniques currently employed have some limiting factors, such as the need for high temperatures (T > 500 °C) or vacuum systems. For this reason in this work has been investigated the growth of Si nanostructures through the combination of a cost-effective technique like electrochemical deposition with the properties of liquid Ga as catalyst for the crystallization. Electrodeposition has been performed successfully on different substrates and for different temperatures and voltages. The results have been analyzed through SEM, EDX and XPS revealing a correlation between temperature/voltage and the oxidation state and homogeneity of the deposition. The actual effect of Ga in the process is not clear, but seems that under the current conditions is not really playing a role. Further experiments are planned to better understand the system and hopefully obtaining crystalline Si nanostructures exploiting the role of Ga as catalyst.ope

Hypogammaglobulinaemia secondary to cow-milk allergy in children under 2 years of age

Symptomatic hypogammaglobulinaemia in children younger than 2 years of age was studied to rule out a primary immunodeficiency. Thirty-four patients were referred to the Immunology Service to study the hypogammaglobulinaemia- associated clinical picture. Food allergy was documented in 10 patients by personal and familial history, presence of specific immunoglobulin E (IgE) and elevated total serum IgE levels. Coeliac disease and human immunodeficiency virus infection were also ruled out. Protein loss through stools was assessed by clearance of α1-antitrypsin (AAT). Serum immunoglobulin levels were determined by nephelometry and functional antibodies were studied by enzyme-linked immunosorbent assay. The cellular immune response was assessed by in vitro lymphocyte proliferation in response to mitogens and cell subsets were analysed by flow cytometry. In five patients of the 10 patients we suspected a protein loss through the mucosa. Four of these five patients showed an increased AAT and the other showed an extensive cutaneous lesion. Immunological studies revealed normal antibody function, in vitro lymphoproliferative responses and cell numbers in four of the 5 patients. One patient showed abnormally low numbers of CD4+ T cells as well as a defective proliferative response to mitogens. After diagnosis of cow milk allergy, milk was replaced with infant milk formula containing hydrolysed proteins. Recovery of immunoglobulin values and clinical resolution were achieved. Hypogammaglobulinaemia during early childhood in some children may be secondary to cow milk allergy, and immunoglobulins and cells may leak through the inflamed mucosa. Resolution of symptoms as well as normalization of immunoglobulin values may be easily achieved by avoidance of the offending allergen.Laboratorio de Investigaciones del Sistema Inmun

Hypogammaglobulinaemia secondary to cow-milk allergy in children under 2 years of age

Symptomatic hypogammaglobulinaemia in children younger than 2 years of age was studied to rule out a primary immunodeficiency. Thirty-four patients were referred to the Immunology Service to study the hypogammaglobulinaemia- associated clinical picture. Food allergy was documented in 10 patients by personal and familial history, presence of specific immunoglobulin E (IgE) and elevated total serum IgE levels. Coeliac disease and human immunodeficiency virus infection were also ruled out. Protein loss through stools was assessed by clearance of α1-antitrypsin (AAT). Serum immunoglobulin levels were determined by nephelometry and functional antibodies were studied by enzyme-linked immunosorbent assay. The cellular immune response was assessed by in vitro lymphocyte proliferation in response to mitogens and cell subsets were analysed by flow cytometry. In five patients of the 10 patients we suspected a protein loss through the mucosa. Four of these five patients showed an increased AAT and the other showed an extensive cutaneous lesion. Immunological studies revealed normal antibody function, in vitro lymphoproliferative responses and cell numbers in four of the 5 patients. One patient showed abnormally low numbers of CD4+ T cells as well as a defective proliferative response to mitogens. After diagnosis of cow milk allergy, milk was replaced with infant milk formula containing hydrolysed proteins. Recovery of immunoglobulin values and clinical resolution were achieved. Hypogammaglobulinaemia during early childhood in some children may be secondary to cow milk allergy, and immunoglobulins and cells may leak through the inflamed mucosa. Resolution of symptoms as well as normalization of immunoglobulin values may be easily achieved by avoidance of the offending allergen.Laboratorio de Investigaciones del Sistema Inmun

Interface Modification for Energy Levels Alignment and Charge Extraction in CsPbI3_3 Perovskite Solar Cells

In perovskite solar cells (PSCs) energy levels alignment and charge extraction at the interfaces are the essential factors directly affecting the device performance. In this work, we present a modified interface between all-inorganic CsPbI$_3$ perovskite and its hole selective contact (Spiro-OMeTAD), realized by a dipole molecule trioctylphosphine oxide (TOPO), to align the energy levels. On a passivated perovskite film, by n-Octyl ammonium Iodide (OAI), we created an upward surface band-bending at the interface by TOPO treatment. This improved interface by the dipole molecule induces a better energy level alignment and enhances the charge extraction of holes from the perovskite layer to the hole transport material. Consequently, a Voc of 1.2 V and high-power conversion efficiency (PCE) of over 19% were achieved for inorganic CsPbI$_3$ perovskite solar cells. Further, to demonstrate the effect of the TOPO dipole molecule, we present a layer-by-layer charge extraction study by transient surface photovoltage technique (trSPV) accomplished by charge transport simulation.Comment: 20 pages, 4 Figure

Halogen Bonded Hole Transport Material Suppresses Charge Recombination and Enhances Stability of Perovskite Solar Cells

Interfaces play a crucial role in determining perovskite solar cells, PSCs performance and stability. It is therefore of great importance to constantly work toward improving their design. This study shows the advantages of using a hole transport material HTM that can anchor to the perovskite surface through halogen bonding XB . A halo functional HTM PFI is compared to a reference HTM PF , identical in optoelectronic properties and chemical structure but lacking the ability to form XB. The interaction between PFI and perovskite is supported by simulations and experiments. XB allows the HTM to create an ordered and homogenous layer on the perovskite surface, thus improving the perovskite HTM interface and its energy level alignment. Thanks to the compact and ordered interface, PFI displays increased resistance to solvent exposure compared to its not interacting counterpart. Moreover, PFI devices show suppressed nonradiative recombination and reduced hysteresis, with a Voc enhancement of bigger equal as 20 mV and a remarkable stability, retaining more than 90 efficiency after 550 h of continuous maximum power point tracking. This work highlights the potential that XB can bring to the context of PSCs, paving the way for a new halo functional design strategy for charge transport layers, which tackles the challenges of charge transport and interface improvement simultaneousl

Electrochemical growth of Silicon nanostructures for photovoltaic applications

Silicon is the most widely used material for current photovoltaic (PV) panel manufacturing. Next generation solar cells will be obtained by creating novel device structures, material fabrication processes and implementing new physical principles. In this regard, semiconductor nanostructures have shown their potential for achieving efficient solar energy conversion at low cost due to their particular and tunable optical properties. Nevertheless, most of the fabrication techniques currently employed have some limiting factors, such as the need for high temperatures (T > 500 °C) or vacuum systems. For this reason in this work has been investigated the growth of Si nanostructures through the combination of a cost-effective technique like electrochemical deposition with the properties of liquid Ga as catalyst for the crystallization. Electrodeposition has been performed successfully on different substrates and for different temperatures and voltages. The results have been analyzed through SEM, EDX and XPS revealing a correlation between temperature/voltage and the oxidation state and homogeneity of the deposition. The actual effect of Ga in the process is not clear, but seems that under the current conditions is not really playing a role. Further experiments are planned to better understand the system and hopefully obtaining crystalline Si nanostructures exploiting the role of Ga as catalyst

Refractive index change dominates the transient absorption response of metal halide perovskite thin films in the near infrared

Perovskites have lately attracted a lot of attention as promising materials for the next-generation of efficient, low-cost, and solution processable optoelectronics. Their complex transient photophysics, in time scales ranging from femtoseconds to seconds, have been widely investigated. However, in most of the reported works the spectral window of ultrafast transient absorption (TA) spectroscopy of perovskite films is limited to the visible region, hence missing crucial information coming from the near-infrared (NIR). Furthermore, the measured TA responses are affected by light interference in a thin perovskite layer making data interpretation a challenge even in the visible part of the spectrum. Here, we demonstrate a method that allows us to separately obtain the changes in absorption and refractive index from conventional transmission and reflection pump–probe measurements. We show that the contribution of the absorption change to the response of metal halide perovskite thin films in the NIR is much smaller than that of the refractive index change. Furthermore, the spectral shape of TA responses in the NIR range is predominantly determined by perovskite layer thickness and its refractive index. However, the time profile of the responses bears important information on the carrier dynamics and makes the NIR a useful range to study perovskite photophysics.publishedVersionPeer reviewe

Structure-induced optoelectronic properties of phenothiazine-based materials

Phenothiazine (PTZ)-based materials have recently received considerable interest owing to their intriguing optoelectronic properties, low-cost, versatility of functionalization, and commercial availability. The advent of molecular engineering concepts in π-conjugated organic materials, such as the “donor-acceptor” approach, propelled the synthesis of a large number of PTZ-derivatives with tailored properties like low bandgap, tunable energy levels, and reversible redox properties. This resulted in the promising application of PTZs as electron donors or acceptors in organic solar cells or as hole-transporting materials in organic light-emitting diodes and perovskite solar cells. In this review, we discuss the recent and most appealing design strategies of PTZ-based materials for optoelectronics, with emphasis on the impact of the structural modifications on the fundamental physicochemical properties (absorption, emission, frontier energy levels, charge carrier mobility). We also highlight the key achievements in the development of solar cells, light-emitting diodes, and batteries employing PTZ core semiconductors. Our final goal is to underpin the reasons that still limit the performance of PTZ-based optoelectronics and to outline future research directions for the next-generation PTZ materials with ever enhanced properties.publishedVersionPeer reviewe