Iván García

A 32.6% efficient lattice-matched dual-junction solar cell working at 1000 suns

Photovoltaic conversion efficiencies of 32.6% and 30% at concentrations of 1000 and 3500 suns, respectively, are achieved in monolithic GaInP/GaAs dual-junction solar cells grown lattice matched on a GaAs substrate by metal-organic vapor-phase epitaxy. The tunnel-junction design, based on an (Al)GaAs/GaAs heterojunction, is found to be a key factor for achieving this efficiency at such high concentrations. Moreover, the thorough design and joint optimization of the front grid and the top-cell emitter, using quasi-three-dimensional distributed models, also plays a major role. Efficiencies of over 40% at 1000 suns should be achieved by extending this approach to triple-junction devices.

Te doping of GaAs using metalorganic vapor phase epitaxy: Volatile versus nonvolatile behavior

The incorporation of Te into the crystal lattice, when it is used as an n-type dopant for GaAs grown by metalorganic vapor phase epitaxy, is studied. For this purpose, several growth temperatures, total pressures, growth rates, and substrate misorientations have been analyzed, from which it is concluded that depending on the substrate misorientation and total pressure used, the Te behaves like a volatile dopant or a nonvolatile dopant as result of the enhancement or minimization of its adsorption onto the growth surface.

Optimization of the silicon subcell for III-V on silicon multijunction solar cells: Key differences with conventional silicon technology

Dual-junction solar cells formed by a GaAsP or GaInP top cell and a silicon (Si) bottom cell seem to be attractive candidates to materialize the long sought-for integration of III-V materials on Si for photovoltaic (PV) applications. Such integration would offer a cost breakthrough for PV technology, unifying the low cost of Si and the efficiency potential of III-V multijunction solar cells. The optimization of the Si solar cells properties in flat-plate PV technology is well-known; nevertheless, it has been proven that the behavior of Si substrates is different when processed in an MOVPE reactor In this study, we analyze several factors influencing the bottom subcell performance, namely, 1) the emitter formation as a result of phosphorus diffusion; 2) the passivation quality provided by the GaP nucleation layer; and 3) the process impact on the bottom subcell PV properties.

Integration of III-V materials on silicon substrates for multi-junction solar cell applications

The work presented here aims to reduce the cost of multijunction solar cell technology by developing ways to manufacture them on cheap substrates such as silicon. In particular, our main objective is the growth of III-V semiconductors on silicon substrates for photovoltaic applications. The goal is to create a GaAsP/Si virtual substrates onto which other III-V cells could be integrated with an interesting efficiency potential. This technology involves several challenges due to the difficulty of growing III-V materials on silicon. In this paper, our first work done aimed at developing such structure is presented. It was focused on the development of phosphorus diffusion models on silicon and on the preparation of an optimal silicon surface to grow on it III-V materials.

Experimental and modeling analysis of internal luminescence in III-V solar cells

In high quality solar cells, the internal luminescence can be harnessed to enhance the overall performance. Internal confinement of the photons can lead to an increased open-circuit voltage and short-circuit current. Alternatively, in multijunction solar cells the photons can be coupled from a higher bandgap junction to a lower bandgap junction for enhanced performance. We model the solar cell as an optical cavity and compare calculated performance characteristics with measurements. We also describe how very high luminescent coupling alleviates the need for top-cell thinning to achieve current-matching.

Distributed Simulation of Real Tunnel Junction Effects in Multi-Junction Solar Cells

In this paper, we present an improved 3D distributed model that considers real operation regimes in a tunnel junction. This advanced method is able to accurately simulate the high concentrations at which the current in the solar cell surpasses the peak current of the tunnel junction. Simulations of dual‐junction solar cells were carried out with different light profiles and including chromatic aberration to show the capabilities of the model. Such simulations show that, under some circumstances, the solar cell short circuit current may be slightly higher than the tunnel junction peak current without showing the characteristic dip in the J‐V curve. This behavior is caused by the lateral current spreading towards the dark regions, which occurs through the anode region of the tunnel junction.

Multidisciplinary development of robotic surgery in a University Tertiary Hospital: Organization and outcomes

Background: Da Vinci system (Intuitive Surgical ® ) is a surgical telemanipulator providing many technical advantages over conventional laparoscopic approach (3-D vision, ergonomics, highly precise movements, endowrist instrumentation…) and it is currently applied to several specialties throughout the world since 2000. The first Spanish public hospital incorporating this robotic technology was Hospital Clinico San Carlos (HCSC) in

Modelling of lattice matched dilute nitride 4-junction concentrator solar cells on Ge substrates

Technology Computer Aided Design modeling is used to examine the performance under light concentration of a 4-J solar cell Ge-based that includes a 1-eV MBE-grown dilute nitride subcell. The 1-eV solar cell is modeled and examined by using material parameters extracted from detailed electro-optical characterization prior to be included into a multijunction structure. The modelling reveals the impact of the electric field-assisted collection in the performance of single junction solar cells and its effect when included in a 4-Junction solar cells. This effect is responsible for the lower FF (~15% lower) in the 4J when including the dilute nitride subcell, especially if it limits the photocurrent. Finally, an optimization procedure based on dilute nitrides with higher material quality is performed resulting in a 4-Junction solar cell with an efficiency of 47% for concentrations between 1000-2000 suns direct terrestrial spectrum.

Field spectra binning for energy production calculations and multijunction solar cell design

Annual spectra sets must be used for accurate energy production prediction and multijunction solar cell design for maximum energy production at a specific site. These spectra sets contain a large quantity of data that is cumbersome to manage during solar cell design calculations and impractical to reproduce in solar simulators for indoor energy production measurements. However, it should be possible to bin together spectra with similar spectral contents, and then use this reduced set with little loss of accuracy. We present two binning algorithms which judiciously bin together similar spectra to create a much smaller “proxy” set, for which the total measurement time, energy production calculation and solar cell optimization decreases to a matter of seconds. These algorithms are assessed against their accuracy in representing the whole spectra sets for solar cell design and energy production prediction. We find that a set of just five spectra fulfills this requirement. In addition, the sets of proxy spectra act as “fingerprints” of specific sites, and provide an efficient and effective way to understand how cell design and performance vary from site to site. Furthermore, the process of reducing a full data set to a few proxy spectra can help assess the quality of the dataset for multijunction applications, and contribute to improvements to the datasets and data collection methods.

Desarrollo multidisciplinario de la cirugía robótica en un hospital universitario de tercer nivel: organización y resultados

Background Da Vinci system (Intuitive Surgical®) is a surgical telemanipulator providing many technical advantages over conventional laparoscopic approach (3-D vision, ergonomics, highly precise movements, endowrist instrumentation…) and it is currently applied to several specialties throughout the world since 2000. The first Spanish public hospital incorporating this robotic technology was Hospital Clinico San Carlos (HCSC) in Madrid, in July 2006. We present the multidisciplinary organization and clinical, research and training outcomes of the Robotic Surgery Plan developed in the HCSC.BACKGROUND Da Vinci system (Intuitive Surgical) is a surgical telemanipulator providing many technical advantages over conventional laparoscopic approach (3-D vision, ergonomics, highly precise movements, endowrist instrumentation...) and it is currently applied to several specialties throughout the world since 2000. The first Spanish public hospital incorporating this robotic technology was Hospital Clinico San Carlos (HCSC) in Madrid, in July 2006. We present the multidisciplinary organization and clinical, research and training outcomes of the Robotic Surgery Plan developed in the HCSC. MATERIAL AND METHODS Starting from joint management and joint scrub nurses team, General and Digestive Surgery, Urology and Gynaecology Departments were progressively incorporated into the Robotic Surgery Plan, with several procedures increasing in complexity. A number of intra and extra-hospital teaching and information activities were planned to report on the Robotic Surgery Plan. RESULTS Between July 2006 and July 2008, 306 patients were operated on: 169 by General Surgery, 107 by Urology and 30 by Gynaecology teams. The outcomes showed feasibility and a short learning curve. The educational plan included residents and staff interested in robotic technology application. CONCLUSION The structured and gradual incorporation of robotic surgery throughout the PCR-HCSC has made it easier to learn, to share designed infrastructure, to coordinate information activities and multidisciplinary collaboration. This preliminary experience has shown the efficiency of an adequate organization and motivated team.