Perovskite and quantum dot tandem solar cells with interlayer modification for improved optical semitransparency and stability

In this work, four-terminal (4T) tandem solar cells were fabricated by using a methylammonium lead iodide (MAPbI₃) perovskite solar cell (PSC) as the front-cell and a lead sulfide (PbS) colloidal quantum dot solar cell (CQDSC) as the back-cell. Different modifications of the tandem interlayer, at the interface between the sub-cells, were tested in order to improve the infrared transparency of the perovskite sub-cell and consequently increase the utilization of infrared (IR) light by the tandem system. This included the incorporation of a semi-transparent thin gold electrode (Au) on the MAPbI₃ solar cell, followed by adding a molybdenum(vi) oxide (MoO₃) layer or a surlyn layer. These interlayer modifications resulted in an increase of the IR transmittance to the back cell and improved the optical stability, compared to that in the reference devices. This investigation shows the importance of the interlayer, connecting the PSC with a strong absorption in the visible region and the CQDSC with a strong infrared absorption to obtain efficient next-generation tandem photovoltaics (PVs).

Understanding and Controlling the Crystallization Process in Reconfigurable Plasmonic Superlattices

The crystallization of nanomaterials is a primary source of solid-state, photonic structures. Thus, a detailed understanding of this process is of paramount importance for the successful application of photonic nanomaterials in emerging optoelectronic technologies. While colloidal crystallization has been thoroughly studied, for example, with advanced in situ electron microscopy methods, the noncolloidal crystallization (freezing) of nanoparticles (NPs) remains so far unexplored. To fill this gap, in this work, we present proof-of-principle experiments decoding a crystallization of reconfigurable assemblies of NPs at a solid state. The chosen material corresponds to an excellent testing bed, as it enables both in situ and ex situ investigation using X-ray diffraction (XRD), transmission electron microscopy (TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), atomic force microscopy (AFM), and optical spectroscopy in visible and ultraviolet range (UV-vis) techniques. In particular, ensemble measurements with small-angle XRD highlighted the dependence of the correlation length in the NPs assemblies on the number of heating/cooling cycles and the rate of cooling. Ex situ TEM imaging further supported these results by revealing a dependence of domain size and structure on the sample preparation route and by showing we can control the domain size over 2 orders of magnitude. The application of HAADF-STEM tomography, combined with in situ thermal control, provided three-dimensional single-particle level information on the positional order evolution within assemblies. This combination of real and reciprocal space provides insightful information on the anisotropic, reversibly reconfigurable assemblies of NPs. TEM measurements also highlighted the importance of interfaces in the polydomain structure of nanoparticle solids, allowing us to understand experimentally observed differences in UV-vis extinction spectra of the differently prepared crystallites. Overall, the obtained results show that the combination of in situ heating HAADF-STEM tomography with XRD and ex situ TEM techniques is a powerful approach to study nanoparticle freezing processes and to reveal the crucial impact of disorder in the solid-state aggregates of NPs on their plasmonic properties.

A method for studying pico to microsecond time-resolved core-level spectroscopy used to investigate electron dynamics in quantum dots

Time-resolved photoelectron spectroscopy can give insights into carrier dynamics and offers the possibility of element and site-specific information through the measurements of core levels. In this paper, we demonstrate that this method can access electrons dynamics in PbS quantum dots over a wide time window spanning from pico- to microseconds in a single experiment carried out at the synchrotron facility BESSY II. The method is sensitive to small changes in core level positions. Fast measurements at low pump fluences are enabled by the use of a pump laser at a lower repetition frequency than the repetition frequency of the X-ray pulses used to probe the core level electrons: Through the use of a time-resolved spectrometer, time-dependent analysis of data from all synchrotron pulses is possible. Furthermore, by picosecond control of the pump laser arrival at the sample relative to the X-ray pulses, a time-resolution limited only by the length of the X-ray pulses is achieved. Using this method, we studied the charge dynamics in thin film samples of PbS quantum dots on n-type MgZnO substrates through time-resolved measurements of the Pb 5d core level. We found a time-resolved core level shift, which we could assign to electron injection and charge accumulation at the MgZnO/PbS quantum dots interface. This assignment was confirmed through the measurement of PbS films with different thicknesses. Our results therefore give insight into the magnitude of the photovoltage generated specifically at the MgZnO/PbS interface and into the timescale of charge transport and electron injection, as well as into the timescale of charge recombination at this interface. It is a unique feature of our method that the timescale of both these processes can be accessed in a single experiment and investigated for a specific interface.

Opinion of Nursing Students of the University of Bydgoszcz in Poland About the Transplantation of Living Liver Donors

INTRODUCTION

Liver transplantation from living liver donation (LLD) has become an important source of liver grafts.

MATERIAL AND METHOD

We studied the 2011-2012 academic year attitude of nursing students from a university in Poland. The sampling points were compulsory attendance in the 5 nursing courses. The validated questionnaire was Project Collaborative International Donor-Living Liver Donation Rios. The questionnaire was completed anonymously and was self-administered.

RESULTS

The completion rate was 89% (440 of 495); 91% (n = 398) were in favor of the related LLD, 8% (n = 37) were undecided, and 1% (n = 5) were against. When the attitude toward LLD is not related, 40% (n = 177) of respondents were in favor. The favorable attitude was associated with the following: consideration of the needs of organs for transplantations are covered (P ≤ .001); attitude in favor toward organ donation and transplantation (ODT) (P = .001); attitude in favor toward LLD (P = .007); attitude in favor of the acceptance of a LLD by a family member (P = .001); discussion of ODT with the family (P ≤ .001); being in favor of donating organs of a relative (P ≤ .001); and being Catholic (P = .003). After multivariate analysis, we observed the following significant correlations: the thought that the needs of transplantation organs are covered (odds ratio [OR] = 4.608; P = .020); being ready to accept a liver from a LLD (OR = 3.125; P = .038); discussion with the family about the subject of donation and transplantation (OR = 3.215; P = .003); and not belonging to any doctrine or religious belief (OR = 11.363; P = .039).

CONCLUSIONS

In this study 91% of nursing students were in favor of living organ donation.