High Power-Conversion Efficiency of Lead-Free Perovskite Solar Cells: A Theoretical Investigation

Solar cells based on lead-free perovskite have demonstrated great potential for next-generation renewable energy. The SCAPS-1D simulation software was used in this study to perform novel device modelling of a lead-free perovskite solar cell of the architecture ITO/WS₂/CH₃NH₃SnI₃/P3HT/Au. For the performance evaluation, an optimization process of the different parameters such as thickness, bandgap, doping concentration, etc., was conducted. Extensive optimization of the thickness and doping density of the absorber and electron transport layer resulted in a maximum power-conversion efficiency of 33.46% for our designed solar cell. Because of the short diffusion length and higher defect density in thicker perovskite, an absorber thickness of 1.2 µm is recommended for optimal solar cell performance. Therefore, we expect that our findings will pave the way for the development of lead-free and highly effective perovskite solar cells.

Solution-processed two-dimensional materials for next-generation photovoltaics

In the ever-increasing energy demand scenario, the development of novel photovoltaic (PV) technologies is considered to be one of the key solutions to fulfil the energy request. In this context, graphene and related two-dimensional (2D) materials (GRMs), including nonlayered 2D materials and 2D perovskites, as well as their hybrid systems, are emerging as promising candidates to drive innovation in PV technologies. The mechanical, thermal, and optoelectronic properties of GRMs can be exploited in different active components of solar cells to design next-generation devices. These components include front (transparent) and back conductive electrodes, charge transporting layers, and interconnecting/recombination layers, as well as photoactive layers. The production and processing of GRMs in the liquid phase, coupled with the ability to "on-demand" tune their optoelectronic properties exploiting wet-chemical functionalization, enable their effective integration in advanced PV devices through scalable, reliable, and inexpensive printing/coating processes. Herein, we review the progresses in the use of solution-processed 2D materials in organic solar cells, dye-sensitized solar cells, perovskite solar cells, quantum dot solar cells, and organic-inorganic hybrid solar cells, as well as in tandem systems. We first provide a brief introduction on the properties of 2D materials and their production methods by solution-processing routes. Then, we discuss the functionality of 2D materials for electrodes, photoactive layer components/additives, charge transporting layers, and interconnecting layers through figures of merit, which allow the performance of solar cells to be determined and compared with the state-of-the-art values. We finally outline the roadmap for the further exploitation of solution-processed 2D materials to boost the performance of PV devices.

Highly Luminescent WS2 Quantum Dots/ZnO Heterojunctions for Light Emitting Devices

Sonication induced vertical fragmentation of two-dimensional (2D) WS₂ nanosheets into highly luminescent, monodispered, zero-dimensional (0D) quantum dots (QDs) is reported. The formation of 0D structures from 2D sheets and their surface/microstructure characterization are revealed from their microscopic and spectroscopic investigations. Size dependent optical properties of WS₂ nanostructures have been explored by UV-vis absorption and photoluminescence spectroscopy. Interestingly, it is observed that, below a critical dimension (∼2 nm), comparable to the Bohr exciton radius, the tiny nanocrystals exhibit strong emission. Finally, the electroluminescence characteristics are demonstrated for the first time, by forming a heterojunction of stabilizer free WS₂ QDs and ZnO thin films. The signature of white light emission in the light emitting device is attributed to the adequate intermixing of emission characteristics of WS₂ QDs and ZnO. The observation of white electroluminescence may pave the way to fabricate prototype futuristic efficient light emitting devices.

Facile synthesis of optical pH-sensitive molybdenum disulfide quantum dots

An effective fabrication of MoS2 quantum dots (QDs) has been developed using alkali metal-intercalation and exfoliation. The obtained MoS2 QDs are monolayers with a uniform lateral size of 4.26 ± 0.96 nm, which exhibit distinct blue fluorescence with a quantum yield of 2.28%, robust dispersibility, storage stability and pH dependent optical properties.

High Pressure Vibrational Properties of WS2 Nanotubes

We bring together synchrotron-based infrared and Raman spectroscopies, diamond anvil cell techniques, and an analysis of frequency shifts and lattice dynamics to unveil the vibrational properties of multiwall WS2 nanotubes under compression. While most of the vibrational modes display similar hardening trends, the Raman-active A1g breathing mode is almost twice as responsive, suggesting that the nanotube breakdown pathway under strain proceeds through this displacement. At the same time, the previously unexplored high pressure infrared response provides unexpected insight into the electronic properties of the multiwall WS2 tubes. The development of the localized absorption is fit to a percolation model, indicating that the nanotubes display a modest macroscopic conductivity due to hopping from tube to tube.

Self-doped 3-hexylthiophene-b-sodium styrene sulfonate block copolymer: synthesis and its organization with CdSe quantum dots

A strategy was developed for producing a conjugated polymer with both doped stability during repeated electric cycle and compatibility with inorganic semiconductor materials.