Jin, C.; Martin, I.; Calle, E.; Ortega, P.; Lopez, G.; Alcubilla, R. European Photovoltaic Solar Energy Conference and Exhibition p. 805-810 DOI: 10.4229/EUPVSEC20172017-2CV.2.6 Data de presentació: 2017-09-27 Presentació treball a congrés
Reducing the wafer thickness for c-Si solar cell fabrication is an effective approach for cost-savings. Interdigitated Back Contacts (IBC) technology is a promising candidate to be applied to thin c-Si substrates due to its potential to facilitate thin device processing: thin c-Si solar cell could be processed attached to a glass with its rear surface, where all the contacts are to be defined, still accessible. The understanding of thin IBC c-Si solar cell performance has great significance in guiding the design of such devices. In this work, we explore the performance of thin IBC c-Si solar cells by both 3D TCAD device simulations and experimental fabrication based on conventional technology developed in our research group. On one hand, an optical model is proposed using 2D ray tracing method whose results are applied to 3D ATLAS TCAD simulator which is used to simulate the electrical performance of the devices. As a result, efficiencies in the range of 20 % are expected for substrates of 10-20 µm without changing our technology. On the other hand, a ~30 µm IBC solar cell is fabricated by thinning down a previously developed IBC c-Si solar cell on conventional thick high quality substrates demonstrating a 12.1% of efficiency. The front surface passivation provided by Al2O3 is deduced by comparing with the simulation results revealing a front surface recombination velocity of about 1500 cm/s.
Savin, H.; Repo, P.; von Gastrow, G.; Ortega, P.; Calle, E.; Garin, M.; Alcubilla, R. Nature nanotechnology Vol. 10, p. 624-628 DOI: 10.1038/NNANO.2015.89 Data de publicació: 2015-05-18 Article en revista
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 to integrate black silicon into solar cells have resulted in cell efficiencies well 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 excellent 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 real potential for industrial production. Furthermore, we show that the use of black silicon can result in a 3% increase in daily energy production when compared with a reference cell with the same efficiency, due to its better angular acceptance.
Calle, E.; Ortega, P.; Lopez, G.; Martin, I.; Carrió, D.; Voz, C.; Orpella, A.; Puigdollers, J.; Alcubilla, R. Spanish Conference on Electron Devices p. 1-4 DOI: 10.1109/CDE.2015.7087509 Data de presentació: 2015-02 Presentació treball a congrés
In this work we describe a baseline fabrication process of interdigitated-back-contact c-Si(p) solar cells, which combines conventional diffusion oven stages to define base p+ and emitter n+ regions at the backside, with front surface passivation using atomic layer deposited Al2O3 films on textured surfaces with random pyramids. Very low reflectance with outstanding surface recombination velocity values around 3 cm/s are achieved in our precursors. Fabricated solar cells reach efficiencies up to 20.3% (AM1.5G 1 kW/m2, T=25°C), with short circuit density Jsc, open circuit voltage Voc and fill factor FF of 40.6 mA/cm2, 648 mV and 77.2% respectively.
Ortega, P.; Calle, E.; von Gastrow, G.; Repo, P.; Carrió, D.; Savin, H.; Alcubilla, R. Progress in photovoltaics Vol. 23, num. 11, p. 1448-1457 DOI: 10.1002/pip.2664 Data de publicació: 2015 Article en revista
This work demonstrates the high potential of Al2O3 passivated black silicon in high-efficiency interdigitated back contacted
(IBC) solar cells by reducing surface reflectance without jeopardizing surface passivation. Very low reflectance values, below
0.7% in the 300–1000 nm wavelength range, together with striking surface recombination velocities values of 17 and
5 cm/s on p-type and n-type crystalline silicon substrates, respectively, are reached. The simultaneous fulfillment of requirements,
low reflectance and low surface recombination, paves the way for the fabrication of high-efficiency IBC Si solar
cells using black silicon at their front surface. Outstanding photovoltaic efficiencies over 22% have been achieved both
in p-type and n-type 9-cm2 cells. 3D simulations suggest that efficiencies of up to 24% can be obtained in the future with
minor modifications in the baseline fabrication process.
Masmitja, G.; Ortega, P.; Lopez, G.; Calle, E.; Garcia, F.; Martin, I.; Orpella, A.; Voz, C.; Alcubilla, R. Spanish Conference on Electron Devices p. 329-332 DOI: 10.1109/CDE.2013.6481409 Data de presentació: 2013 Presentació treball a congrés
In this work we study the fabrication and characterization of boron diffused emitters using FZ c-Si(n) substrates. Emitter surface was passivated with Al2O3(25 nm thick) layers deposited by thermal atomic layer deposition ALD technique. This study covers a broad emitter sheet resistance Rsh range from 20 to 250 O/sq using both polished and textured wafers. Emitter electrical quality was tested by means of lifetime measurements using quasi-stationary photoconductance QSS-PC method. Dark saturation emitter current densities Joe's were extracted from lifetime measurements resulting in Joe's values ranging from 10 to 150 fA/cm2 depending on Rsh. These results are in the-state-of-the-art in boron emitter passivation.
In this work we study the fabrication and characterization of boron diffused emitters using FZ c-Si(n) substrates. Emitter surface was passivated with Al2O3(25 nm thick) layers deposited by thermal atomic layer deposition ALD technique. This study covers a broad emitter sheet resistance Rsh range from 20 to 250 Ω/sq using both polished and textured wafers. Emitter electrical quality was tested by means of lifetime measurements using quasi-stationary photoconductance QSS-PC method. Dark saturation emitter current densities Joe's were extracted from lifetime measurements resulting in Joe's values ranging from 10 to 150 fA/cm2 depending on Rsh. These results are in the-state-of-the-art in boron emitter passivation.