Alexis De Vos

On the CdS/CuInSe2 conduction band discontinuity

Recent calculations of the electron affinity difference between CdS and CuInSe2 indicate that the conduction band (CB) minimum of CuInSe2 is below the CB minimum of CdS. As a consequence, a spike occurs in the CB at the CdS/CuInSe2 interface. Such a spike is commonly considered as in conflict with good photovoltaic performance of heterojunction solar cells. It is outlined here that the simple assumption of thermionic emission across the junction can explain an unimpeded electron transport in the case of an n+p structure (n‐type window, p‐type absorber), even when a spike in the CB occurs.

A reversible carry-look-ahead adder using control gates

In principle, any reversible logic circuit can be built by using a single building block (having three logic inputs and three logic outputs). However, no simple synthesis tool is available to tell us how a particular logic operation has to be composed of such unit. We demonstrate that, for a flexible design, it is more advantageous to use a broad class of reversible gates, called control gates. They form a generalization of Feynmans three gates (i.e. the NOT, the CONTROLLED NOT, and the CONTROLLED CONTROLLED NOT). As an illustration, a 320-transistor reversible 4-bit carry-look-ahead adder in 0.8 µm c-MOS has been built.

Reversible Computing: Fundamentals, Quantum Computing, and Applications

Written by one of the few top internationally recognized experts in the field, this book concentrates on those topics that will remain fundamental, such as low power computing, reversible programming languages, and applications in thermodynamics. It describes reversible computing from various points of view: Boolean algebra, group theory, logic circuits, low-power electronics, communication, software, quantum computing. It is this multidisciplinary approach that makes it unique.Backed by numerous examples, this is useful for all levels of the scientific and academic community, from undergraduates to established academics.

Generating the group of reversible logic gates

Reversible logic plays a fundamental role both in ultra-low power electronics and in quantum computing. It is therefore important to have an insight into the structure of the group formed by the reversible logic gates and their cascading into reversible circuits. Such insight is gained from constructing chains of maximal subgroups. The subgroup of control gates plays a prominent role, as it is a Sylow 2-subgroup.

On the ideal performance of solar cells with larger-than-unity quantum efficiency.

We investigate the performance of an ideal solar cell taking into account the possibility of pair generation by impact ionization such that one incident photon can give rise to more than one electron-hole pair.

Improved model for solar cells with down-conversion and down-shifting of high-energy photons

A system for converting high-energy incident photons into photons of lower energy was proposed by Trupke et al (2002 J. Appl. Phys. 92 1668). In the present paper we re-analyse this system by using a more elaborate model. The main conclusions of this work are as follows. (1) When non-radiative recombination is neglected, our results confirm the findings of Trupke et al. Both the front and rear down-converter systems improve the performance of a single mono-facial solar cell. However, the present model shows that the conversion efficiency is smaller than estimated before. (2) When both the cell and the front (or rear) converter have the same low radiative recombination efficiency, their combination does not increase the cell conversion efficiency. (3) Adding a converter with a high (near unity) value of the radiative recombination efficiency to a solar cell shows beneficial effects. (4) In this case (i) for high-quality solar cells, the combination cell-rear converter provides a higher efficiency than the combination front converter-solar cell whereas (ii) for low quality solar cells, the front converter system performs better than the rear converter system. Conclusions (3) and (4) may be dependent on the details of the model adopted here.

The endoreversible theory of solar energy conversion: a tutorial

Abstract In the present tutorial, solar energy conversion is described in the framework of endoreversible thermodynamics, i.e. a recently developed subset of irreversible thermodynamics. From a general thermo-chemical endoreversible engine, we deduce the photovoltaic, the photothermal and the photochemical solar energy converter, besides of a few other, non-solar devices.

Influence of some design parameters on the efficiency of solar cells with down-conversion and down shifting of high-energy photons

In this paper we analyze the system proposed by Trupke et al. [J. Appl. Phys. 92, 1668 (2002)] to increase solar cell efficiency. The system consists of adding to the solar cell a so-called down-converter, which is a device able to convert the high-energy incident photons into photons of lower energy. The contribution consists of taking account (i) the nonradiative recombination in both solar cell and converter, (ii) the refractive index of solar cell and converter materials, and (iii) the solar radiation concentration. Two configurations are studied: the cell and rear converter (C-RC) and front converter and cell (FC-C). The main conclusions of this work are as follow. (1) For ideal down-converters, with radiative recombination only, the solar energy conversion efficiency may be, or may not be, increased by adding a front (or a rear) down-converter to the cell, depending on the value of the solar cell refractive index. (2) More realistic systems, where nonradiative recombinations exist inside the convert...

Reversible computing: from mathematical group theory to electronical circuit experiment

Reversible logic gates of a certain logic width w form a group (isomorphic to the symmetric group of order (2 w )!). Study of the subgroups of this group both teaches us a lot about properties of reversible gates and guides us to synthesize particular circuits. After design, circuits are implemented in prototype silicon chips.

Young subgroups for reversible computers

We consider the symmetric group