Migration of cations induces reversible performance losses over day/night cycling in perovskite solar cells

Perovskites have been demonstrated in solar cells with a power conversion efficiency of well above 20​%, which makes them one of the strongest contenders for next generation photovoltaics. While there are no concerns about their efficiency, very little is known about their stability under illumination and load. Ionic defects and their migration in the perovskite crystal lattice are some of the most alarming sources of degrdn., which can potentially prevent the commercialization of perovskite solar cells (PSCs)​. In this work, we provide direct evidence of elec. field-​induced ionic defect migration and we isolate their effect on the long-​term performance of state-​of-​the-​art devices. Supported by modeling, we demonstrate that ionic defects, migrating on timescales significantly longer (above 103 s) than what has so far been explored (from 10-​1 to 102 s)​, abate the initial efficiency by 10-​15​% after several hours of operation at the max. power point. Though these losses are not negligible, we prove that the initial efficiency is fully recovered when leaving the device in the dark for a comparable amt. of time. We verified this behavior over several cycles resembling day​/night phases, thus probing the stability of PSCs under native working conditions. This unusual behavior reveals that research and industrial stds. currently in use to assess the performance and the stability of solar cells need to be adjusted for PSCs. Our work paves the way for much needed new testing protocols and figures of merit specifically designed for PSCs

Impact of the first wave of the SARS-CoV-2 pandemic on the outcome of neurosurgical patients: A nationwide study in Spain

Objective To assess the effect of the first wave of the SARS-CoV-2 pandemic on the outcome of neurosurgical patients in Spain. Settings The initial flood of COVID-19 patients overwhelmed an unprepared healthcare system. Different measures were taken to deal with this overburden. The effect of these measures on neurosurgical patients, as well as the effect of COVID-19 itself, has not been thoroughly studied. Participants This was a multicentre, nationwide, observational retrospective study of patients who underwent any neurosurgical operation from March to July 2020. Interventions An exploratory factorial analysis was performed to select the most relevant variables of the sample. Primary and secondary outcome measures Univariate and multivariate analyses were performed to identify independent predictors of mortality and postoperative SARS-CoV-2 infection. Results Sixteen hospitals registered 1677 operated patients. The overall mortality was 6.4%, and 2.9% (44 patients) suffered a perioperative SARS-CoV-2 infection. Of those infections, 24 were diagnosed postoperatively. Age (OR 1.05), perioperative SARS-CoV-2 infection (OR 4.7), community COVID-19 incidence (cases/10 5 people/week) (OR 1.006), postoperative neurological worsening (OR 5.9), postoperative need for airway support (OR 5.38), ASA grade =3 (OR 2.5) and preoperative GCS 3-8 (OR 2.82) were independently associated with mortality. For SARS-CoV-2 postoperative infection, screening swab test <72 hours preoperatively (OR 0.76), community COVID-19 incidence (cases/10 5 people/week) (OR 1.011), preoperative cognitive impairment (OR 2.784), postoperative sepsis (OR 3.807) and an absence of postoperative complications (OR 0.188) were independently associated. Conclusions Perioperative SARS-CoV-2 infection in neurosurgical patients was associated with an increase in mortality by almost fivefold. Community COVID-19 incidence (cases/10 5 people/week) was a statistically independent predictor of mortality. Trial registration number CEIM 20/217

Low-voltage, high-brightness and deep-red light-emitting electrochemical cells (LECs) based on new ruthenium(II) phenanthroimidazole complexes

Light-Emitting Electrochemical Cells (LECs) with a simple device structure ITO/Ru complex/Ga: In were prepared by using heteroleptic ruthenium(II) complexes containing 2-(2-hydroxyphenyl)-1(4-bromophenyl)-1h-imidazo[4,5-f][1,10] phenanthroline (hpbpip) as the pi-extended ligand. After ancillary ligand modification, the [Ru(hpbpip)(dmbpy)(2)](ClO4)(2) complex shows a deep red electro-luminescence emission (2250 cd m(-2) at 6 V) centered at 685 nm, 65 nm red-shifted compared to the [Ru(bpy)(3)](ClO4)(2) benchmark red-emitter at a very low turn voltage (2.6 V), demonstrating its potential for low-cost deep-red light sources. Moreover, the PL quantum yield of the [Ru(hpbpip)(bpy)(2)](ClO4)(2) complex was revealed to be higher (0.121) than the benchmark standard [Ru(bpy)(3)](2+) (0.095)

Ruthenium phenanthroimidazole complexes for near infrared light-emitting electrochemical cells

By adding different electron donor moieties to the ancillary ligand in ruthenium(II) phenanthroimidazole complexes, we successfully designed near infrared light emitting complexes suitable for light emitting electro-chemical cells (LECs). By using a single-layer LEC architecture and incorporating a novel top contact via melted deposition, working devices were obtained without the addition of any hole or electron transport layer. The resulting devices exhibited a dramatic reduction in the turn-on voltage from 3.1 V to 2.3 V, which is the lowest value observed in the ruthenium phenanthroline family. With the substitution of suitable groups on the ancillary ligand, the electroluminescence wavelength was shifted from the red (617 nm) to the near Infrared (NIR) region (700 nm), with the highest efficacy of 0.45 cd A(-1) and external quantum efficiency (EQE) of 1.367%. These values are the highest for NIR-LECs based on ruthenium polypyridyl complexes reported so far

Minimization of Carrier Losses for Efficient Perovskite Solar Cells through Structural Modification of Triphenylamine Derivatives

Three hole transport materials (HTMs) based on a substituted triphenylamine moiety have been synthesized and successfully employed in triple-cation mixed-halide PSCs, reaching efficiencies of 19.4 %. The efficiencies, comparable to those obtained using spiro-OMeTAD, point them out as promising candidates for easily attainable and cost-effective alternatives for PSCs, given their facile synthesis from commercially available materials. Interestingly, although all these HTMs show similar chemical and physical properties, they provide different carrier recombination kinetics. Our results demonstrate that is feasible through the molecular design of the HTM to minimize carrier losses and, thus, increase the solar cell efficiencies

Introduction of a Bifunctional Cation Affords Perovskite Solar Cells Stable at Temperatures Exceeding 80 degrees C

Perovskite solar cells (PSCs) with high efficiencies have been reported in recent years. Consequently, the main obstacle that hinders their commercialization is their poor thermal stability. Here, we describe the introduction of an A-site cation (2-choloroethylammonium) that affords an ABX(3) perovskite, which is stable at high temperatures (>80 degrees C) while achieving efficiencies > 19% in methylammonium lead iodide (MAPI)-based PSCs

Metal-Oxide-Free Methylammonium Lead Iodide Perovskite-Based Solar Cells: the Influence of Organic Charge Transport Layers

Metal-oxide-free methylammonium lead iodide perovskite-based solar cells are prepared using a dual-source thermal evaporation method. This method leads to high quality reproducible films with large crystal domain sizes allowing for an in depth study of the effect of perovskite film thickness and the nature of the electron and hole blocking layers on the device performance. The power conversion efficiency increases from 4.7% for a device with only an organic electron blocking layer to almost 15% when an organic hole blocking layer is also employed. In addition to the in depth study on small area cells, larger area cells (approx. 1 cm(-2)) are prepared and exhibit efficiencies in excess of 10%

Optoelectronic device comprising guanidinium in the organic-inorganic perovskite

Organic-inorganic lead halide perovskites have shown impressive power conversion efficiency (PCE) in a range of solar cell architectures. Despite the multiple ionic compositions that have been reported so far, the presence of organic constituents is an essential element in all the high efficiency formulations, with the methylammonium (MA) and formamidinium (FA) cations being the sole realistic options available to date. In this study, we demonstrate a novel three-dimensional (3D) perovskite with improved material stability as a result of the incorporation of an alternative organic cation, guanidinium, into the MAPb3 crystal structure. The new MA1_xGuaxPbl3 perovskite shows enhanced thermal stability and intrinsically new structural and optoelectronic properties. This allows for stable and high-power conversion efficiencies over 20%, a fundamental step within the perovskite field

Highly efficient perovskite solar cells with a compositionally engineered perovskite​/hole transporting material interface

Perovskite solar cells (PSCs) have experienced an outstanding advance in power conversion efficiency (PCE) by optimizing the perovskite layer morphol., compn., interfaces, and charge collection efficiency. To enhance PCE, here we developed a new method i.e., engineering a compositional gradient thinly at the rear interface between the perovskite and the hole transporting materials. We demonstrate that charge collection is improved and charge recombination is reduced by formation of an engineered passivating layer, which leads to a striking enhancement in open-​circuit voltage (VOC)​. The passivation effect induced by constructing an addnl. FAPbBr3-​xIx layer on top of the primary (FAPbI3)​0.85(MAPbBr3)​0.15 film was proven to function as an electron blocking layer within the perovskite film, resulting in a final PCE of 21.3​%. Our results shed light on the importance of the interfacial engineering on the rear surface of perovskite layers and describe an innovative approach that will further boost the PSC efficiency