Ramon Alcubilla | Universitat Politecnica de Catalunya (original) (raw)

Papers by Ramon Alcubilla

Applied Physics Letters, 2012

In this work the Laser Induced Forward Transfer (LIFT) technique is investigated to create n-dope... more In this work the Laser Induced Forward Transfer (LIFT) technique is investigated to create n-doped regions on p-type c-Si substrates. The precursor source of LIFT consisted in a phosphorous-doped hydrogenated amorphous silicon layer grown by Plasma Enhanced Chemical Vapor Deposition (PECVD) onto a transparent substrate. Transfer of the doping atoms occurs when a sequence of laser pulses impinging onto the doped layer propels the material toward the substrate. The laser irradiation not only transfers the doping material but also produces a local heating that promotes its diffusion into the substrate. The laser employed was a 1064 nm, lamp-pumped system, working at pulse durations of 100 and 400 ns. In order to obtain a good electrical performance a comprehensive optimization of the applied laser fluency and number of pulses was carried out. Subsequently, arrays of n + p local junctions were created by LIFT and the resulting J – V curves demonstrated the formation of good quality n+ r...

In this work, we describe a novel fabrication process of p-type interdigitated back contact (IBC)... more In this work, we describe a novel fabrication process of p-type interdigitated back contact (IBC) silicon solar developed by means of laser doping and laser firing techniques. We use dielectric layers both as dopant sources to create highly-doped regions and as passivating layers. In particular, we use phosphorus-doped silicon carbide stacks (a-SiC x (n)) deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) and aluminum oxide (Al 2 O 3 ) layer deposited by atomic layer deposition (ALD). Emitters were fabricated with a light thermal phosphorus diffusion in order to reduce bulk and surface emitter recombination losses. Highly doped regions n ++ (emitter) and p ++ (base) were simultaneously created in a point-like structure using a pulsed Nd-YAG 1064 nm laser in the nanosecond regime by laser processing the dielectric layers. The results obtained for a cell, 3x3 cm 2 , are presented. Efficiencies up to 18.1% ( J sc = 39 mA/cm2, V oc = 632 mV, FF = 73.4%) have been achieved in...

We revisited two different strategies to fabricate 1D photonic crystals of nonlinear optical diel... more We revisited two different strategies to fabricate 1D photonic crystals of nonlinear optical dielectric materials based on ultrafast laser ablation of the surface of an RbTiOPO4 crystal, and selective etching of ferroelectric domains of the surface of a periodically poled LiNbO4 crystal. We evaluated their behaviour as Bragg diffraction gratings. We also presented the recent advances we developed in a new procedure of fabrication of 2D and 3D photonic crystals of KTiOPO4 (KTP) grown on the surface of a KTP substrate by liquid phase epitaxial means within the pores of a silicon macroporous template. Optical, structural, morphological, and compositional characterization for the photonic crystals produced through this technique are presented.

Energy Procedia

District heating networks are commonly addressed in the literature as one of the most effective s... more District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.

Photovoltaic Generators in Space, Nov 1, 1986

ABSTRACT

Physica Status Solidi a Applications and Materials Science, Oct 1, 2008

Solar Energy Materials and Solar Cells, 2015

This work reports on a comparative study comprising three transition metal oxides, MoO 3 , WO 3 a... more This work reports on a comparative study comprising three transition metal oxides, MoO 3 , WO 3 and V 2 O 5 , acting as front p-type emitters for n-type crystalline silicon heterojunction solar cells. Owing to their high work functions (>5 eV) and wide energy band gaps, these oxides act as transparent hole-selective contacts with semiconductive properties that are determined by oxygen-vacancy defects (MoO 3-x), as confirmed by x-ray photoelectron spectroscopy. In the fabricated hybrid structures, 15 nm thick transition metal oxide layers were deposited by vacuum thermal evaporation. Of all three devices, the V 2 O 5 /n-silicon heterojunction performed the best with a conversion efficiency of 15.7% and an open-circuit voltage of 606 mV, followed by MoO 3 (13.6%) and WO 3 (12.5%). These results bring into view a new silicon heterojunction solar cell concept with advantages such as the absence of toxic dopant gases and a simplified low-temperature fabrication process.

Solar Energy Materials and Solar Cells, 2015

We demonstrate that n-type black silicon can be passivated efficiently using atomic layer deposit... more We demonstrate that n-type black silicon can be passivated efficiently using atomic layer deposited (ALD) Al 2 O 3 , reaching maximum surface recombination velocities below 7 cm/s. We show that the low surface recombination velocity results from a higher sensitivity of the nanostructures to surface charge and from the absence of surface damage after black silicon etching. The surface recombination velocity is shown to be inversely proportional to the fourth power of the negative charge in contrast to the quadratic dependence observed in planar surfaces. This effect compensates the impact of the increased surface area in the nanostructures and extends the potential of black silicon for instance to n-type Interdigitated Back Contact (IBC) cells.

Nature Nanotechnology, 2015

The nanostructuring of silicon surfaces-known as black silicon-is a promising approach to elimina... more The nanostructuring of silicon surfaces-known as black silicon-is a promising approach to eliminate front-surface reflection in photovoltaic devices without the need for a conventional antireflection coating. This might lead to both an increase in efficiency and a reduction in the manufacturing costs of solar cells. However, all previous attempts of integrating black silicon into solar cells have resulted in cell efficiencies much below 20% due to the increased charge carrier recombination at the nanostructured surface. Here we show that a conformal alumina film can solve the issue of surface recombination in black silicon solar cells by providing chemical and electrical passivation. We demonstrate that efficiencies above 22% can be reached, even in thick interdigitated back-contacted cells, where carrier transport is very sensitive to front surface passivation. This means that the surface recombination issue has truly been solved and black silicon solar cells have a real potential to industrial production. Furthermore, we show that use of black silicon can result in 3% increase in the daily energy production when compared to a reference cell with the same efficiency, due to its better angular acceptance.

IEE Proceedings G Circuits, Devices and Systems, 1989

ABSTRACT

Applied Surface Science, 2015

In this work laser doping technique is used to create highly-doped regions defined in a point-lik... more In this work laser doping technique is used to create highly-doped regions defined in a point-like structure to form n+/p and p+/n junctions applying a pulsed Nd-YAG 1064 nm laser in the nanosecond regime. In particular, phosphorous-doped silicon carbide stacks (a-SiC x /a-Si:H (n-type)) deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) and aluminum oxide (Al 2 O 3) layers deposited by atomic layer deposition (ALD) on 2 ± 0.5 cm p-and n-type FZ c-Si substrates respectively are used as dopant sources. Laser power and number of pulses per spot are explored to obtain the optimal electrical behavior of the formed junctions. To assess the quality of the p+ and n+ regions, the junctions are electrically contacted and characterized by means of dark J-V measurements. Additionally, a diluted HF treatment previous to front metallization has been explored in order to know its impact on the junction quality. The results show that fine tuning of the energy pulse is critical while the number of pulses has minor effect. In general the different HF treatments have no impact in the diode electrical behavior except for an increase of the leakage current in n+/p junctions. The high electrical quality of the junctions makes laser doping, using dielectric layers as dopant source, suitable for solar cell applications. Particularly, a potential open circuit voltage of 0.64 V (1 sun) is expected for a finished solar cell.

2015 10th Spanish Conference on Electron Devices (CDE), 2015

ABSTRACT This paper presents an 3D TCAD model of crystalline Silicon (c-Si) solar cells. Physical... more ABSTRACT This paper presents an 3D TCAD model of crystalline Silicon (c-Si) solar cells. Physical parameters used in the model are discussed. Simulation results are compared to experimental current-voltage curves and solar cell figures of merit namely open-circuit voltage, short-circuit current density, fill factor, and conversion efficiency, allowing us to determine an optimum design for these devices. Particularly, the model is applied to conventional p-type c-Si solar cells with rear contacts based on Laser-Firing technique and to Doped by Laser (DopLa) crystalline Silicon solar cells.

IEEE Journal of Photovoltaics, 2015

In this work we investigate the effect of the laser-firing process on the back surface passivatio... more In this work we investigate the effect of the laser-firing process on the back surface passivation of p-type silicon heterojunction solar cells. For that purpose, two different nanosecond laser sources radiating at ultraviolet (355 nm) and visible (532 nm) wavelengths are employed. Firstly, we optimize the laser-firing process in terms of the electrical resistance of locally diffused point contacts. Specific contact resistance values as low as 0.91 mΩ⋅cm 2 and 0.57 mΩ⋅cm 2 are achieved for the visible and ultraviolet laser sources, respectively. In addition, the impact of the laser-firing process on the rear surface passivation is studied by analyzing the internal-quantum-efficiency curves of complete devices. Low surface recombination velocities in the range of 300 cm/s are obtained for the ultraviolet laser with a 1% fraction of contacted area. This value increases to about 700 cm/s for the visible laser, which indicates a significantly higher recombination at the contacted area. The best heterojunction solar cells with rear laser-fired contacts are obtained for the ultraviolet laser and reached a 17.5% conversion efficiency.

IEEE Journal of Photovoltaics, 2015

In this work an approach to create laser-fired contacts from aluminum foils is studied on p-type ... more In this work an approach to create laser-fired contacts from aluminum foils is studied on p-type silicon heterojunction solar cells. This alternative approach consists in the use of aluminum foils instead of evaporated layers as a metal source and rear electrode for the laser-firing process. A q-switched infrared laser (1064 nm) was employed to create the local point contacts. Quasi-Steady-State Photoconductance measurements evidenced a limited degradation in the surface passivation quality during the laser-firing process. Heterojunction solar cells fabricated with these rear contacts reached a best conversion efficiency of 18% with a remarkable opencircuit voltage of 690 mV. These values were very close to those of reference devices fabricated with evaporated aluminum layers. This result suggests a similar effect on the rear surface passivation by both contact strategies. However, external quantum efficiency curves revealed a better response of devices with a rear aluminum foil in the near infrared. Optical measurements indicate that this effect can be related to a higher internal reflection at the back surface. Consequently, laser-fired contacts from aluminum foils appear as a fast and convenient solution for the rear contact of high-efficiency silicon solar cells.

Microelectronic Engineering, 2015

In crystalline silicon (c-Si) solar cell field, an intensive effort is being paid to reduce the q... more In crystalline silicon (c-Si) solar cell field, an intensive effort is being paid to reduce the quantity of silicon material used in each cell in order to minimize its costs. With the reduction of wafer thickness, light trapping inside the c-Si absorber becomes more and more necessary. Several photonic structures have been proposed underlining their optical properties. However, addressing other technological issues, like contact formation through the photonic structure, is also necessary for their application into finished devices. In this paper we study the viability of laser firing technique to create solar cell base contacts through inverse opals deposited on the previously passivated rear surface of the device as photonic light trapping structures. Firstly, we check out that electrical surface passivation properties are not degraded during the inverse opals fabrication steps. Next, from SEM images we deduce that the inverse opal is mechanically and thermally stable after laser processing. Moreover, reflectance measurements show that optical properties are also maintained. From these results, we can conclude that inverse opal fabrication is compatible with solar cell technology and that contacts can be created by laser means without damaging the surrounding 3D inverse opal structure neither the silicon below it.

Borull for help in performing the FTIR measurements; the Ministerio de Educación y Ciencia, for s... more Borull for help in performing the FTIR measurements; the Ministerio de Educación y Ciencia, for supporting the work (Grant Nos. MAT2002-04603, TIC2002-04184, MAT2005-06354, and TEC2005-02038). We also acknowledge support from the EC-funded project PHOREMOST (FP6/2003/IST/ 2511616) and J. M. acknowledges support from the Generalitat de Catalunya that funded the work with the "Distinció de La Generalitat de Catalunya per a la promoció de la recerca universitària." COMMUNICATIONS

Solid-State Electronics, 1992

ABSTRACT

Applied Physics Letters, 2012

Energy Procedia

Photovoltaic Generators in Space, Nov 1, 1986

ABSTRACT

Physica Status Solidi a Applications and Materials Science, Oct 1, 2008

Solar Energy Materials and Solar Cells, 2015

Nature Nanotechnology, 2015

IEE Proceedings G Circuits, Devices and Systems, 1989

ABSTRACT

Applied Surface Science, 2015

2015 10th Spanish Conference on Electron Devices (CDE), 2015

IEEE Journal of Photovoltaics, 2015

Microelectronic Engineering, 2015

Solid-State Electronics, 1992

ABSTRACT

This book presents a set of solved examples on semiconductor device physics. Semiconductor device... more This book presents a set of solved examples on semiconductor device physics. Semiconductor devices is a core subject in electrical engineering and physics curricula. The level of the proposed examples corresponds to a semester course at senior undergraduate or junior graduate level. Readers are expected to have a basic background on quantum and solid state physics, moreover a reasonable mathematical knowledge reaching differential equations is also assumed.
There are many excellent text books on semiconductor device physics, however very often the examples are mostly numerical, trying to fix the order of magnitude of the obtained results. In this book, problems with a certain level of complexity are solved and explained step by step presenting at the same time the involved physics. This work does not replace a text book and lecture notes, but it may definitely be a good complement.
At the Universitat Politècnica de Catalunya (BarcelonaTech) one of the authors, R. Alcubilla, has been lecturing on semiconductor devices at different levels for more than 20 years. In particular together with C. Voz started in 2013 a semester course for engineering physics students at senior undergraduate level. This book collects the exercises of the different written tests since 2013.
The level of the students has been always rather high and the acceptation of the course has been also very good. Even if teachers tend to overestimate the motivation of the students, our feeling has been always very positive and the average result of the proposed tests good.
We cannot claim the authorship of all the proposed problems. As most professors know, the process for preparing a test is not easy, trying to question about the different parts of the course, equilibrating the difficulties, looking for interesting questions (the definition of interesting questions is subject of discussion between teacher and students). Some of the problems are
roughly original, classical ones or fruit of the previous experience of the authors, others are adapted from material found in different books, web sites, etc…
R. Alcubilla wants to thank Universitat Politècnica de Catalunya (BarcelonaTech) for a 6 monthssabbatical leave used for writing the biggest part of this book. Finally, we want to thank ourstudents that during these years have “suffered” these exercises.