• Energy Research

In this study we investigate the efficacy of iron gettering as a function of electrically inactive phosphorus in the emitter in combination with low temperature annealing steps. To achieve different amounts of electrically inactive phosphorus in the emitter a highly doped PSG produced emitter with a large plateau depth of electrical active phosphorus is etched back stepwise by a wet-chemical procedure. Therewith we achieve a gradual reduction in electrically inactive phosphorus with small changes in electrically active phosphorus (?Rsh < 4 ?/sq). After this step, the wafers with different emitters have been annealed at 700 °C for 30 min and the content of Feiin the bulk has been measured using QSS-PC. The results show, (i) that for higher amounts of electrically inactive phosphorusa stronger iron gettering effect can be observed and (ii) that an additional annealing step leads to a significant change of Fei. This means, (i) that anelectricallyinactive phosphorus concentration dependence for iron gettering is observed and (ii) additional annealing steps, below the usual diffusion temperature of phosphorus, can be used to reduce interstitial iron in highly contaminated wafers further.

-- ENGLISH VERSION BELOW -- Tras décadas de avances tecnológicos y reducciones en su precio, la energía solar puede competir en el mercado con los combustibles fósiles en muchas regiones del mundo. Sin embargo, falta mucho para que el sol sea una fuente energética principal. Numerosos centros de investigación y empresas trabajan para mejorar la eficiencia de los paneles solares, aumentar su vida útil y producir nuevos materiales. Algunos gobiernos han apostado económicamente y han establecido marcos regulatorios para apoyar dichas innovaciones. La sociedad civil debe tener también un rol central. Tal como a menudo sentencian los movimientos activistas “la revolución energética en manos de la ciudadanía es el camino”. ‘GenerationSolar’ es una iniciativa de ciencia ciudadana, enmarcada en el proyecto europeo GRECO, con dos objetivos principales: a) empoderar a la ciudadanía mediante acciones que fomentan un conocimiento más profundo sobre la energía solar, su investigación y sus usos; y b) establecer una plataforma en la que la propia ciudadanía participe activamente en la investigación. La ciencia ciudadana representa un campo de acción a caballo entre múltiples disciplinas, si bien ha sido desde el sector de la comunicación científica, médica y ambiental desde donde ha sido más activa. Hace ya décadas que se intenta mejorar el equilibrio entre la comunicación unidireccional (el que sabe instruye al que no sabe) y las formas de comunicación más innovadoras basadas en la participación y la colaboración para la acción. GRECO unió a investigadoras, comunicadoras y ciudadanas -a través de encuestas, una hackathon online y desarrollo informático- para lanzar GenerationSolar en el Día de la Tierra 2020: un aplicativo móvil en el cual la ciudadanía registra sus instalaciones y crea una base de datos sobre la producción solar global. A dos meses del lanzamiento, la app cuenta con 71 registros y más de 22 MW de energía reportada. -- ENG -- After decades of technological advances and price reductions, solar energy can compete in the marketplace with fossil fuels in many regions of the world. However, the sun is a long way from being a main energy source. Numerous research centers and companies are working to improve the efficiency of solar panels, increase their useful life and produce new materials. Some governments have gambled economically and established regulatory frameworks to support such innovations. Civil society must also have a central role. As activist movements often state, "the energy revolution in the hands of the citizens is the way." ‘GenerationSolar’ is a citizen science initiative, framed in the European GRECO project, with two main objectives: a) to empower citizens through actions that promote a deeper understanding of solar energy, its research and its uses; and b) to establish a platform in which citizens themselves actively participate in the investigation. Citizen science represents a field of action between multiple disciplines, although it has been from the scientific, medical and environmental communication sector where it has been most active. For decades, attempts have been made to improve the balance between one-way communication (the one who knows teches the one who does not) and the most innovative forms of communication based on participation and collaboration for action. GRECO brought together researchers, communicators and citizens - through surveys, an online hackathon and computer development - to launch GenerationSolar on Earth Day 2020: a mobile application in which citizens register their facilities and create a database on global solar production. Two months after launch, the app has 71 records and more than 22 MW of reported energy.

High-quality multicrystalline Upgraded Metallurgical Grade Silicon (UMG-Si) offers significant advantages over conventional polysilicon-based PV technology, associated to lower cost, lower energy budget and lower carbon footprint. The aim of this study is twofold: on the one hand, to ascertain the efficiency potential of solar cells based on this material in terms of carrier lifetime; and on the other hand, to explore, as a result of that, the adoption of high-efficiency cell architectures by establishing an effective rear-side passivation scheme for the implementation of passivated emitter rear contact (PERC) devices. The carrier lifetime and the surface passivation efficacy are investigated for different passivating layer configurations after single and double P-diffusion gettering processes. Layer stacks consisting of Al2O3, SiOxNy and a-SiNx:H capping overlayers have been optimized, on industrial size, saw-damage-etched UMG wafers and results compared to those obtained using reference iodine-ethanol (IE) passivation. Diagnosis based on minority carrier lifetime and implied Voc (iVoc) measurements helped monitor the impact of parameter optimization on wafer quality, particularly after firing processes. Carrier lifetimes over 600 us at 10^15 cm-3 injection level as well as up to 790 us locally have been measured in UMG-Si wafers passivated with IE after a Phosphorus Diffusion Gettering (PDG), demonstrating the suitability of the material for high-efficiency cell architectures. Values higher than 300 us have been obtained with Al2O3-based passivation layers for gettered UMG wafers, with implied Voc values up to 710 mV. These record-breaking lifetimes and iVoc figures obtained with p-type multicrystalline UMG-Si material demonstrate a significant upgrading of its electronic quality by means of industry-scalable technical processes. Comment: 31 pages, 6 figures

Germanium is a low cost alternative to the highly expensive III-V semiconductors commonly used on thermophotovoltaic (TPV) devices. Despite efficiencies up to 16.5 % have been theorized in previous works, no experimental efficiencies have been reported so far for germanium-based devices. In this work, we present the first TPV germanium efficiency measured in a high view factor calorimetry set up. Efficiencies and power densities up to 11.2 % and 1.43 W/cm2 have been obtained using a graphite emitter heated at 1544 ºC.

Due to its low cost and high possibilities, multicrystalline silicon (mc-Si) is an attractive substrate to produce solar cells. Trying to reach high efficiencies with a simple and repetitive method, we adapted a standard monocrystalline process to multicrystalline material. Different gettering methods (Phosphorous, Aluminium and P and Al co-gettering) have been studied. In our laboratory, 15.2% efficiency have been achieved to date. PC1D simulations shows that, with a reduction of bulk recombination and a better front and rear passivation schemes, efficiencies higher than 18% could be obtained.

Polysilicon production costs contribute approximately to 25–33% of the overall cost of the solar panels and a similar fraction of the total energy invested in their fabrication. Understanding the energy losses and the behaviour of process temperature is an essential requirement as one moves forward to design and build large scale polysilicon manufacturing plants. In this paper we present thermal models for two processes for poly production, viz., the Siemens process using trichlorosilane (TCS) as precursor and the fluid bed process using silane (monosilane, MS). We validate the models with some experimental measurements on prototype laboratory reactors relating the temperature profiles to product quality. A model sensitivity analysis is also performed, and the effects of some key parameters such as reactor wall emissivity and gas distributor temperature, on temperature distribution and product quality are examined. The information presented in this paper is useful for further understanding of the strengths and weaknesses of both deposition technologies, and will help in optimal temperature profiling of these systems aiming at lowering production costs without compromising the solar cell quality. Peer Reviewed

The dissolution and gettering of iron is studied during the final fabrication step of multicrystalline silicon solar cells, the co-firing step, through simulations and experiments. The post-processed interstitial iron concentration is simulated according to the as-grown concentration and distribution of iron within a silicon wafer, both in the presence and absence of the phosphorus emitter, and applying different time-temperature profiles for the firing step. The competing effects of dissolution and gettering during the short annealing process are found to be strongly dependant on the as-grown material quality. Furthermore, increasing the temperature of the firing process leads to a higher dissolution of iron, hardly compensated by the higher diffusivity of impurities. A new defect engineering tool is introduced, the extended co-firing, which could allow an enhanced gettering effect within a small additional time