Alkali treatments of Cu(In,Ga)Se2 thin‐film absorbers and their impact on transport barriers

We study the impact of different alkali post-deposition treatments by thermal admittance spectroscopy and temperature-dependent current-voltage (IVT) characteristics of high-efficiency Cu(In,Ga)Se2thin-film solar cells fabricated from low-temperature and high-temperature co-evaporated absorbers. Capacitance steps observed by admittance spectroscopy for all samples agree with the widely observed N1 signature and show a clear correlation to a transport barrier evident from IVT characteristics measured in the dark, indicating that defects are likely not responsible for these capacitance steps. Activation energies extracted from capacitance spectra and IVT characteristics vary considerably between different samples but show no concise correlation to the alkali species used in the post-deposition treatments. Numerical device simulations show that the transport barrier in our devices might be related to conduction band offsets in the absorber/buffer/window stack

Psychological impact of Covid-19 pandemic on oncological patients: a survey in Northern Italy

The psychological impact of the Covid 19 pandemic on cancer patients, a population at higher risk of fatal consequences if infected, has been only rarely evaluated. This study was conducted at the Departments of Oncology of four hospitals located in the Verona area in Italy to investigate the psychological consequences of the pandemic on cancer patients under active anticancer treatments. A 13-item ad hoc questionnaire to evaluate the psychological status of patients before and during the pandemic was administered to 474 consecutive subjects in the time frame between April 27th and June 7th 2020. Among the 13 questions, 7 were considered appropriate to elaborate an Emotional Vulnerability Index (EVI) that allows to separate the population in two groups (low versus high emotional vulnerability) according to observed median values. During the emergency period, the feeling of high vulnerability was found in 246 patients (53%) and was significantly associated with the following clinical variables: female gender, being under chemotherapy treatment, age 64 65 years. Compared to the pre-pandemic phase, the feeling of vulnerability was increased in 41 patients (9%), remained stably high in 196 (42%) and, surprisingly, was reduced in 10 patients (2%). Overall, in a population characterized by an high level of emotional vulnerability the pandemic had a marginal impact and only a small proportion of patients reported an increase of their emotional vulnerability

Time-resolved photoluminescence on double graded Cu(In,Ga)Se2 – Impact of front surface recombination and its temperature dependence

<p>Time-resolved photoluminescence (TRPL) is applied to determine an effective lifetime of minority charge carriers in semiconductors. Such effective lifetimes include recombination channels in the bulk as well as at the surfaces and interfaces of the device. In the case of Cu(In,Ga)Se₂ absorbers used for solar cell applications, trapping of minority carriers has also been reported to impact the effective minority carrier lifetime. Trapping can be indicated by an increased temperature dependence of the experimentally determined photoluminescence decay time when compared to the temperature dependence of Shockley–Read–Hall (SRH) recombination alone and can lead to an overestimation of the minority carrier lifetime. Here, it is shown by technology computer-aided design (TCAD) simulations and by experiment that the intentional double-graded bandgap profile of high efficiency Cu(In,Ga)Se₂ absorbers causes a temperature dependence of the PL decay time similar to trapping in case of a recombinative front surface. It is demonstrated that a passivated front surface results in a temperature dependence of the decay time that can be explained without minority carrier trapping and thus enables the assessment of the absorber quality by means of the minority carrier lifetime. Comparison with the absolute PL yield and the quasi-Fermi-level splitting (QFLS) corroborate the conclusion that the measured decay time corresponds to the bulk minority carrier lifetime of 250 ns for the double-graded CIGS absorber under investigation.</p

In vitro gastrointestinal gas monitoring with carbon nanotube sensors

In vitro simulators of the human gastrointestinal (GI) tract are remarkable technological platforms for studying the impact of food on the gut microbiota, enabling continuous and real-time monitoring of key biomarkers. However, comprehensive real-time monitoring of gaseous biomarkers&nbsp;in these systems is required with a cost-effective approach, which has been challenging to perform experimentally to date. In this work, we demonstrate the integration and in-line use of carbon nanotube (CNT)-based chemiresitive gas sensors coated with a thin polydimethylsiloxane (PDMS) membrane for the continuous monitoring of gases within the Simulator of the Human Microbial Ecosystem (SHIME). The findings demonstrate the ability of the gas sensor to continuously monitor the different phases of gas production in this harsh, anaerobic, highly humid, and acidic environment for a long exposure time (16&nbsp;h) without saturation. This establishes our sensor platform as an effective tool for real-time monitoring of gaseous biomarkers in in vitro systems like SHIME

RbF post deposition treatment for narrow bandgap Cu(In, Ga)Se-2 solar cells

Multi-junction solar cells are known to have a considerably increased efficiency potential over their typical single junction counterparts. In order to produce low cost and lightweight multi-junction devices, the availability of suitable narrow (< 1.1 eV) bandgap bottom cells is paramount. A possible absorber for such a bottom cell is the Cu(In, Ga)Se-2 (CIGS) compound semiconductor, one of the most efficient thin film materials to date.In this contribution we report on the RbF post deposition treatment of narrow bandgap CIGS absorbers grown with a single bandgap grading approach. We discuss the necessary deposition conditions and the observed improvements on solar cells performance. A certified record efficiency of 18.0% for an absorber with 1.00 eV optoelectronic bandgap is presented and its suitability for perovskite/CIGS tandem devices is shown

Single-graded CIGS with narrow bandgap for tandem solar cells

Multi-junction solar cells show the highest photovoltaic energy conversion efficiencies, but the current technologies based on wafers and epitaxial growth of multiple layers are very costly. Therefore, there is a high interest in realizing multi-junction tandem devices based on cost-effective thin film technologies. While the efficiency of such devices has been limited so far because of the rather low efficiency of semitransparent wide bandgap top cells, the recent rise of wide bandgap perovskite solar cells has inspired the development of new thin film tandem solar devices. In order to realize monolithic, and therefore current-matched thin film tandem solar cells, a bottom cell with narrow bandgap (~1 eV) and high efficiency is necessary. In this work, we present Cu(In,Ga)Se2 with a bandgap of 1.00 eV and a maximum power conversion efficiency of 16.1%. This is achieved by implementing a gallium grading towards the back contact into a CuInSe2 base material. We show that this modification significantly improves the open circuit voltage but does not reduce the spectral response range of these devices. Therefore, efficient cells with narrow bandgap absorbers are obtained, yielding the high current density necessary for thin film multi-junction solar cells