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Extensive literature and publications on intermediate band solar cells (IBSCs) are reviewed. A detailed discussion is given on the thermodynamics of solar energy conversion in IBSCs, the device physics, and the carrier dynamics processes with a particular emphasis on the two-step inter-subband absorption/recombination processes that are of paramount importance in a successful implementation high-efficiency IBSC. The experimental solar cell performance is further discussed, which has been recently demonstrated by using highly mismatched alloys and high-density quantum dot arrays and superlattice. IBSCs having widely different structures, materials, and spectral responses are also covered, as is the optimization of device parameters to achieve maximum performance.

Luminescent solar concentrators (LSCs) generally consist of transparent polymer sheets doped with luminescent species. Incident sunlight is absorbed by the luminescent species and emitted with high quantum efficiency, such that emitted light is trapped in the sheet and travels to the edges where it can be collected by solar cells. LSCs offer potentially lower cost per Wp. This paper reviews results mainly obtained within the framework of the Fullspectrum project. Two modeling approaches are presented, i.e., a thermodynamic and a ray-trace one, as well as experimental results, with a focus on LSC stability.

The fabrication and full characterization of luminescent solar concentrators (LSCs) comprising CdSe core/multishell quantum dots (QDs) is reported. TEM analysis shows that the QDs are well dispersed in the acrylic medium while maintaining a high quantum yield of 45%, resulting in highly transparent and luminescent polymer plates. A detailed optical analysis of the QD-LSCs including absorption, emission, and time-resolved fluorescence measurements is presented. Both silicon and GaAs solar cells attached to the side of the QD-LSCs are used to measure the external quantum efficiency and power conversion efficiency (2.8%) of the devices. Stability tests show only a minor decrease of 4% in photocurrent upon an equivalent of three months outdoor illumination. The optical data are used as input for a ray-trace model that is shown to describe the properties of the QD-LSCs well. The model was then used to extrapolate the properties of the small test devices to predict the power conversion efficiency of a 50×50 cm2 module with a variety of different solar cells. The work described here gives a detailed insight into the promise of QD-based LSCs

In this paper, we propose an innovative concept for solar power conversion—the “photon ratchet” intermediate band solar cell (IBSC)—which may increase the photovoltaicenergy conversion efficiency of IBSCs by increasing the lifetime of charge carriers in the intermediate state. The limiting efficiency calculation for this concept shows that the efficiency can be increased by introducing a fast thermal transition of carriers into a non-emissive state. At 1 sun, the introduction of a “ratchet band” results in an increase of efficiency from 46.8% to 48.5%, due to suppression of entropy generation

Bandgap engineering of strain-balanced InGaAs/GaAsP multiple quantum wells (MQWs) allows high-quality materials with an absorption edge beyond GaAs to be epitaxially grown in Ge/GaAs-based multijunction solar cells. We demonstrate MQW solar cells with effective bandgaps ranging from 1.31 eV to as low as 1.15 eV. The bandgap-voltage-offset of MQWs is found to be independent of effective bandgaps and superior to a bulk reference by approximately 0.1 V. This implies the merit of high photovoltage as compared with bulk cells with the same bandgap in addition to their widely bandgap-tunable property. Towards the realization of fully lattice-matched quad-junction devices, we demonstrate a 70-period, 1.15-eV bandgap MQW cell as a promising material in 0.66/1.15/1.51/1.99-eV quad-junction cells, whose practical efficiency has a potential to achieve over 50%. With such a large period number of MQWs, the reverse-biased external quantum efficiency reaches an average of over 60% in the spectral region corresponding to a 1.15-eV subcell; this is achieved with only a-few-percent drop at short-circuit condition. The device presented here reaches the target open-circuit voltage and over 75% of the current density required for realizing a 1.15-eV subcell in a 50%-efficient quad-junction solar cell. We believe that future devices which exploit light-trapping structures and enhanced carrier extraction will be able to reach the desired target.

Porosity, one of the important quality attributes of pharmaceutical tablets, directly affects the mechanical properties, the mass transport and hence tablet disintegration, dissolution and ultimately the bioavailability of an orally administered drug. The ability to accurately and quickly monitor the porosity of tablets during manufacture or during the manufacturing process will enable a greater assurance of product quality. This tutorial systematically outlines the steps involved in the terahertz-based measurement method that can be used to quantify the porosity of a tablet within seconds in a non-destructive and non-invasive manner. The terahertz-based porosity measurement can be performed using one of the three main methods, which are (i) the zero-porosity approximation (ZPA); (ii) the traditional Bruggeman effective medium approximation (TB-EMA); and (iii) the anisotropic Bruggeman effective medium approximation (AB-EMA). By using a set of batches of flat-faced and biconvex tablets as a case study, the three main methods are compared and contrasted. Overall, frequency-domain signal processing coupled with the AB-EMA method was found to be most suitable approach in terms of accuracy and robustness when predicting the porosity of tablets over a range of complexities and geometries. This tutorial aims to concisely outline all the necessary steps, precautions and unique advantages associated with the terahertz-based porosity measurement method.

Computational models can provide significant insight into the operation mechanisms and deficiencies of photovoltaic solar cells. Solcore is a modular set of computational tools, written in Python 3, for the design and simulation of photovoltaic solar cells. Calculations can be performed on ideal, thermodynamic limiting behaviour, through to fitting experimentally accessible parameters such as dark and light IV curves and luminescence. Uniquely, it combines a complete