No abstract

Tandem solar cells (TSCs) have attracted prodigious attention for their high efficiency, which can surmount the Shockley–Queisser limit for single-junction solar cells. Flexible TSCs are lightweight and cost-effective, and are considered a promising approach for a wide range of applications. In this paper, a numerical model, based on TCAD simulation, is presented to assess the performance of a novel two-terminal (2T) all-polymer/CIGS TSC. To confirm the model, the obtained simulation results were compared with standalone fabricated all-polymer and CIGS single solar cells. Common properties of the polymer and CIGS complementary candidates are their non-toxicity and flexibility. The initial top all-polymer solar cell had a photoactive blend layer (PM7:PIDT), the optical bandgap of which was 1.76 eV, and the initial bottom cell had a photoactive CIGS layer, with a bandgap of 1.15 eV. The simulation was then carried out on the initially connected cells, revealing a power conversion efficiency (PCE) of 16.77%. Next, some optimization techniques were applied to enhance the tandem performance. Upon treating the band alignment, the PCE became 18.57%, while the optimization of polymer and CIGS thicknesses showed the best performance, reflected by a PCE of 22.73%. Moreover, it was found that the condition of current matching did not necessarily meet the maximum PCE condition, signifying the essential role of full optoelectronic simulations. All TCAD simulations were performed via an Atlas device simulator, where the light illumination was AM1.5G. The current study can offer design strategies and effective suggestions for flexible thin-film TSCs for potential applications in wearable electronics.

Introducing high speed networks, such as the fifth generation of mobile technology and related applications including the internet of things, creates a pressing demand for hardware infrastructure that provides sufficient bandwidth. Here, silicon-based microwave-photonics presents a solution that features easy and inexpensive fabrication through a mature platform that has long served the electronics industry. In this work, the design of an electro-optic modulator is proposed where the ‘fin’ structure is adopted from the domain of electronics devices, with emphasis on the high speed of operation. The proposed modulator is customized to provide a bandwidth of 90 GHz with a small phase shifter length of 800 μm and an optical insertion loss of 4 dB. With such a speed, this proposed modulator fits high-speed applications such as modern tele-communications systems.

The low bandgap antimony selenide (Sb2Se3) and wide bandgap organic solar cell (OSC) can be considered suitable bottom and top subcells for use in tandem solar cells. Some properties of these complementary candidates are their non-toxicity and cost-affordability. In this current simulation study, a two-terminal organic/Sb2Se3 thin-film tandem is proposed and designed through TCAD device simulations. To validate the device simulator platform, two solar cells were selected for tandem design, and their experimental data were chosen for calibrating the models and parameters utilized in the simulations. The initial OSC has an active blend layer, whose optical bandgap is 1.72 eV, while the initial Sb2Se3 cell has a bandgap energy of 1.23 eV. The structures of the initial standalone top and bottom cells are ITO/PEDOT:PSS/DR3TSBDT:PC71BM/PFN/Al, and FTO/CdS/Sb2Se3/Spiro-OMeTAD/Au, while the recorded efficiencies of these individual cells are about 9.45% and 7.89%, respectively. The selected OSC employs polymer-based carrier transport layers, specifically PEDOT:PSS, an inherently conductive polymer, as an HTL, and PFN, a semiconducting polymer, as an ETL. The simulation is performed on the connected initial cells for two cases. The first case is for inverted (p-i-n)/(p-i-n) cells and the second is for the conventional (n-i-p)/(n-i-p) configuration. Both tandems are investigated in terms of the most important layer materials and parameters. After designing the current matching condition, the tandem PCEs are boosted to 21.52% and 19.14% for the inverted and conventional tandem cells, respectively. All TCAD device simulations are made by employing the Atlas device simulator given an illumination of AM1.5G (100 mW/cm2). This present study can offer design principles and valuable suggestions for eco-friendly solar cells made entirely of thin films, which can achieve flexibility for prospective use in wearable electronics.

Temperature dependence of the characteristics of a Schottky-barrier carbon nanotube field effect transistor has been investigated in detail. This study was performed using two-dimensional quantum simulator based on self-consistent solution of non-equilibrium Green's function formalism with Poisson's equation. From discrepancy in performance of ON and OFF states with temperature, it was concluded that the main dominant component of the conduction mechanism in the OFF state is the thermionic emission while in the ON-state is the tunnelling mechanism. Also, the temperature dependence of the frequency response was studied. They found that the temperature enhances the cutoff frequency. Compact models for OFF current and subthreshold swing with temperature are also proposed and compared with the numerical results.