Progress on Low-Temperature Pulsed Electron Deposition of CuInGaSe2 Solar Cells

The quest for single-stage deposition of CuInGaSe2 (CIGS) is an open race to replace very effective but capital intensive thin film solar cell manufacturing processes like multiple-stage coevaporation or sputtering combined with high pressure selenisation treatments. In this paper the most recent achievements of Low Temperature Pulsed Electron Deposition (LTPED), a novel single stage deposition process by which CIGS can be deposited at 250 °C, are presented and discussed. We show that selenium loss during the film deposition is not a problem with LTPED as good crystalline films are formed very close to the melting temperature of selenium. The mechanism of formation of good ohmic contacts between CIGS and Mo in the absence of any MoSe2 transition layers is also illustrated, followed by a brief summary of the measured characteristics of test solar cells grown by LTPED. The 17% efficiency target achieved by lab-scale CIGS devices without bandgap modulation, antireflection coating or K-doping is considered to be a crucial milestone along the path to the industrial scale-up of LTPED. The paper ends with a brief review of the open scientific and technological issues related to the scale-up and the possible future applications of the new technology

Method and apparatus for producing thin films on a substrate via pulsed electron deposition process

Description: Pulsed Electron Deposition (PED) is a technique for the growth of conductive and dielectric thin film materials (thickness of few tenths and a few tens of microns). This technique is based on the generation of a pulsed beam of high-energy electrons (1-25 keV), and the subsequent collimation of the material towards a multi-target composed by the desired elemental stoichiometry. The interaction between the beam and the target leads to an evaporation of the material from the target towards a substrate placed parallel to the surface of the target. The stoichiometry of the target is transferred completely to the evaporating phase only if this latter is produced under conditions far from thermodynamic equilibrium. This condition is obtained if the thermal transient achieved on the surface of the target material by the interaction with the e-beam is as high as possible. The surface thermal transient depends on the power of the electron beam, hence on the extraction voltage and on the beam current. This dependence is linear in the case of conductive targets, while in the case of dielectric ones, the thermal transient reaches a maximum value at a given value of current. The novelties of this patent are a method and a device for in situ measurement of the beam current, leading to the possibility of maximizing the ablation process and increasing the reproducibility of the interaction between electrons and target, thus the stoichiometry of the film. Main applications: The device described in the patent can be useful in the field of material physics, especially in the material science area (electronics, sensors, photovoltaic and magnetism), in the case of growth techniques based on electron beams. Main Advantages: The object of this patent is original and innovative, as it introduces a new non-destructive in situ diagnostics for the deposition of thin films by pulsed electron beam technique (PED), also known as PPD (Pulsed Plasma Deposition) or CSA (Channel Spark Ablation). The advantages of the diagnostic method developed are: 1) it does not affect the deposition process, and 2) it allows to know the real-time e-beam current, 3) and hence to control all the variables associated with it (rate control , area of deposition, energy of the evaporated, etc.).Descrizione: La deposizione da elettroni pulsati (PED, Pulsed Electron Deposition) ? una tecnica di tipo fisico per la realizzazione di strati sottili di materiali conduttivi e dielettrici (spessore compreso tra qualche decimo e qualche decina di micron). Tale tecnica si basa sulla generazione di un fascio pulsato di elettroni ad alta energia (1-25 keV), e la successiva collimazione di quest\u27ultimo verso un materiale target multi-elementale con una determinata stechiometria. L\u27interazione tra il fascio e il target d? origine all\u27evaporazione del materiale dal target verso un substrato posto parallelamente alla superficie del target stesso ad alcuni centimetri di distanza. La stechiometria del target si trasferisce completamente nei vapori prodotti solo se questi ultimi sono prodotti in condizioni lontane dall\u27equilibrio termodinamico. Questa condizione si ottiene se il transiente di riscaldamento prodotto sulla superficie del materiale target dall\u27interazione con il fascio elettronico ? il pi? alto possibile. Il transiente termico superficiale dipende dalla potenza del fascio elettronico, quindi dal voltaggio di estrazione e dalla corrente elettronica. Questa dipendenza ? lineare nel caso di target conduttivi, mentre nel caso dei dielettrici il transiente raggiunge un valore massimo per un dato valore di corrente. Il trovato consiste in un metodo ed un\u27apparecchiatura per misurare in situ la corrente di fascio, consentendo di massimizzare il processo di ablazione e di aumentare la riproducibilit? dell\u27interazione tra elettroni e target, quindi della stechiometria del film. Usi Principali: L\u27apparecchiatura descritta nel brevetto si presta per essere utilizzata nel campo del settore della fisica dei materiali, in particolare nel campo della crescita di materiali per applicazioni in elettronica, sensoristica, magnetismo e fotovoltaico, in presenza di una tecnica di deposizione di film sottili basata sull\u27utilizzo di fasci elettronici. Vantaggi Principali: Il trovato ? originale e innovativo, in quanto introduce un nuovo sistema non distruttivo di diagnostica in situ del processo di deposizione di film sottili ad elettroni pulsati (PED), conosciuto anche come PPD (Pulsed Plasma Deposition) o CSA (Channel Spark Ablation). I vantaggi del metodo diagnostico ideato sono: 1) non influisce sul processo di deposizione, e 2) consente di conoscere in tempo reale la corrente del fascio, 3) dando la possibilit? di controllare tutte le grandezze connesse con quest\u27ultima (velocit? di deposizione, area di deposizione, energia del materiale evaporato, etc.),4) migliorando cos? la riproducibilit? del processo

InP-based lattice-matched InGaAsP and strain-compensated InGaAs∕InGaAs quantum well cells for thermophotovoltaic applications

Quantum well cells (QWCs) for thermophotovoltaic (TPV) applications are demonstrated in the InGaAsP material system lattice matched to the InP substrate and strain-compensated InGaAs/InGaAs QWCs also on InP substrates. We show that lattice-matched InGaAsP QWCs are very well suited for TPV applications such as with erbia selective emitters. QWCs with the same effective band gap as a bulk control cell show a better voltage performance in both wide and erbialike emission. We demonstrate a QWC with enhanced efficiency in a narrow-band spectrum compared to a bulk heterostructure control cell with the same absorption edge. A major advantage of QWCs is that the band gap can be engineered by changing the well thickness and varying the composition to the illuminating spectrum. This is relatively straightforward in the lattice-matched InGaAsP system. This approach can be extended to longer wavelengths by using strain-compensation techniques, achieving band gaps as low as 0.62 eV that cannot be achieved with lattice-matched bulk material. We show that strain-compensated QWCs have voltage performances that are at least as good as, if not better than, expected from bulk control cells

Luminescent Solar Concentrators - Cylindrical Design

Luminescent solar concentrators (LSCs) are typically planar low-concentration systems that absorb sunlight over a large area and emit a red-shifted spectrum out of smaller surfaces, where solar cells can be attached. We present the study of a composite system, in which a linear geometrical concentrator is used as primary device to focus sunlight onto a cylindrical LSC encased in a transparent matrix. The idea behind this design is to reduce re-absorption losses, which generally limit the performance of LSCs. Experimental measurements on a cylindrical LSC were compared with a raytrace model, showing a good agreement. Further predictions were made based on the model. It was shown how the reduction of re-absorption losses is achieved by allowing the luminescence from the cylindrical core to travel in the transparent matrix. The proposed design can achieve high optical concentrations with the need for only one-dimensional tracking.JRC.DG.F.8-Renewable Energy (Ispra

InGaAs/InGaAs strain-compensated quantum well cells for thermophotovoltaic applications

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Investigation of Strain Relaxation Mechanisms in InGaAs/GaAs Single Layer Films

In this work a strict comparison of the results obtained on InGaAs/GaAs heterostructures by HRXRD and RBS-channeling analysis shows a discrepancy in the In atomic fraction determined by the two techniques. The discrepancy leads to a difference in the reference lattice parameter of the relaxed film and, therefore, changes the description of the strain relaxation rate. After a discussion on the possible reasons for this discrepancy, the results have been interpreted as the influence of the atomic degrees of freedom internal to the lattice unit cell which could determinate the equilibrium shape of the unit cell. While it has been not strictly proved, the most reasonable hypothesis to explain the experimental results is that local ordering leads to a relaxed unit cell which is slightly tetragonal