An electronic ratchet is required in nanostructured intermediate band solar cells

We investigate in this letter the intrinsic properties that have limited the efficiency of nanostructured intermediate band solar cells. Those devices take advantage of intra-band transitions, which occur on narrow energy width, and present low radiative recombination efficiency. We derive the minimum requirements in terms of those two characteristics to achieve efficiencies in excess of the Shockley-Queisser limit, and show that compatible nanostructures are challenging to obtain. Especially, we evidence that currently experimentally considered materials cannot overcome the best single junction cells. In order to solve those issues, we consider devices including an electronic ratchet mechanism. Firstly, such devices are shown to be much less sensitive on the limitations of the nanostructures characteristics, so that requirements for high efficiencies can be met. Secondly, we show that quantum well devices present advantages over their quantum dots counterparts, although they have attracted much less interest so far

Generalized Reciprocity Relations in Solar Cells with Voltage-Dependent Carrier Collection: Application to p-i-n Junction Devices

Two reciprocity theorems are important for fundamental understanding of the solar cell operation and applications to device evaluation: (1) the carrier-transport reciprocity connecting the dark-carrier injection with the short-circuit photocarrier collection and (2) the optoelectronic reciprocity connecting the electroluminescence with the photovoltaic quantum efficiency at short circuit. These theorems, however, fail in devices with thick depletion regions such as p-i-n junction solar cells. By properly linearizing the carrier-transport equation in such devices, we report that the dark-carrier injection is related to the photocarrier collection efficiency at the operating voltage, not at short circuit as suggested in the original theorem. This leads to the general form of the optoelectronic reciprocity relation connecting the electroluminescence with the voltage-dependent quantum efficiency, providing a correct interpretation of the optoelectronic properties of p-i-n junction devices. We also discuss the validity of the well-known relation between the open-circuit voltage and the external luminescence efficiency. The impact of illumination intensity and device parameters on the validity of the reciprocity theorems is quantitatively investigated

Beneficial impact of a thin tunnel barrier in quantum well intermediate-band solar cell

Based on electronic quantum transport modeling, we study the transition between the intermediate-band and the conduction-band in nano-structured intermediate-band solar cell. We show that a tunnel barrier between the quantum well (QW) and the host material could improve the current. The confinement generated by such a barrier favors the inter-subband optical coupling in the QW and then changes the excitation-collection trade-off. More surprisingly, we also show that tunneling impacts the radiative recombination and then the voltage. Using a detailed balance model we explain and we propose a broadening factor for this Voc modification. Finally we show that a thin tunnel barrier is beneficial for both current and voltage

Hot Carrier Solar Cell: From Simulation to Devices

International audienceSingle junction III-V heterostructures based devices could overtake the Shockley-Queisser limit if thermalisation of photogenerated carriers can be strongly limited as in the hot carrier solar cell concept. Previous modelling and experiments have shown the interest of Multiple Quantum Wells heterostructures in the antimonide system and the importance of very thin structures. In this paper we report new data on the thermalisation rates in antimonide and phosphide heterostructures measured at ambient temperature. For the first time electrical control of hot carrier population is performed on hot carrier heterostructures device

Visualization and suppression of interfacial recombination for high-efficiency large-area pin perovskite solar cells

The performance of perovskite solar cells is predominantly limited by non-radiative recombination, either through trap-assisted recombination in the absorber layer or via minority carrier recombination at the perovskite/transport layer interfaces. Here, we use transient and absolute photoluminescence imaging to visualize all non-radiative recombination pathways in planar pin-type perovskite solar cells with undoped organic charge transport layers. We find significant quasi-Fermi-level splitting losses (135 meV) in the perovskite bulk, whereas interfacial recombination results in an additional free energy loss of 80 meV at each individual interface, which limits the open-circuit voltage (V) of the complete cell to ~1.12 V. Inserting ultrathin interlayers between the perovskite and transport layers leads to a substantial reduction of these interfacial losses at both the p and n contacts. Using this knowledge and approach, we demonstrate reproducible dopant-free 1 cm perovskite solar cells surpassing 20% efficiency (19.83% certified) with stabilized power output, a high V (1.17 V) and record fill factor (>81%)

Dispositif a Semi-Conducteur Avec Structure De Passivation Des Surfaces Recombinantes

La présente invention concerne un dispositif à semi-conducteur (110), comportant une jonction p-n (12), ladite jonction p-n comprenant une première (16) et une deuxième (17) couches sensiblement planes, au contact l'une de l'autre, définissant une direction d'empilement (Z), chacune des première et deuxième couches comprenant un bord latéral (22, 24), lesdits bords latéraux étant sensiblement dans un prolongement l'un de l'autre selon la direction d'empilement. Le dispositif comporte en outre une structure de passivation (113), telle que la première couche (16) est disposée entre ladite structure de passivation et la deuxième couche (17) selon la direction d'empilement, ladite structure de passivation étant configurée de sorte à générer dans la jonction p-n une zone de déplétion sensiblement annulaire à proximité du bord latéral des première et deuxième couches, ladite zone de déplétion entourant une zone centrale non déplétée

Development of new methods of optoelectronic characterization of solar cells

The photovoltaic energy is expected to represent an important part of our future energy sources. To improve its competitiveness, we aim at improving its efficiency and reducing the costs. To this purpose, new characterization methods are needed, both at the industry and research levels. We take advantage in this thesis of the solar cells photoluminescence (PL) and electroluminescence (EL) emissions. To acquire these light fluxes, a hyperspectral imager is developed, which records spectrally resolved images, with an absolute calibration. Therefore the luminescence is measured in photons, per units of energy, time and surface. Analysis methods are developed and validated on high efficiencies gallium arsenide cells. From PL measurements, maps of the pn junction saturation currents are determined contactless. Using the EL, carriers collection efficiency and layer resistivity are probed. Standard measurement methods confirm these results. Eventually, the developed methods are applied to copper indium gallium diselenide solar cells. Such absorbers are strongly inhomogeneous, while presenting high efficiencies. Their mechanisms are not fully understood, and can be investigated by luminescence based characterization methods. For the first time, maps of the quasi-Fermi level splitting are determined from PL records. By comparison with the EL emission, collection and material quality issues can be differentiated at the micrometer scale.L énergie photovoltaïque est appelée à prendre une place importante dans notre futur mix énergétique. Pour augmenter sa compétitivité, l objectif est d en augmenter le rendement et de diminuer les coûts. Dans ce but, de nouvelles méthodes de caractérisations sont développées, pour une utilisation à la fois industrielle et au niveau de la recherche. Nous exploitons ici l émission de photoluminescence (PL) et d électroluminescence (EL) des cellules solaires. Pour l acquisition du flux émis un imageur hyperspectral est développé, dont la particularité d acquérir des images résolues spectralement, avec une calibration absolue. La luminescence est donc mesurée en photons, par unité d énergie, de temps et de surface. Des méthodes d analyse sont ensuite développées et validées sur une cellule haut rendement à base d arséniure de gallium. A partir de la PL, nous déterminons sans contacts et avec une résolution spatiale les courants de saturation de la jonction pn. En EL, des grandeurs caractéristiques de collection des porteurs et de résistivité sont accessibles. Des mesures classiques viennent confirmer ces résultats. Enfin, ces méthodes sont appliquées à des cellules à base d absorbeur de diséléniure de cuivre, d indium et de gallium. Ce matériau est fortement inhomogène tout en présentant des rendements élevés. Ses mécanismes de fonctionnement restent encore méconnus, que des méthodes de caractérisation par luminescence peuvent éclairer. Pour la première fois, nous déterminons des cartographies de la tension délivrée par la cellule en PL. Par comparaison avec le signal d EL, nous pouvons décorréler les problèmes de collection et de qualité du matériau à l échelle micrométrique.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF