Browsing by Author "Salome, Pedro M. P."
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- Decoupling of Optical and Electrical Properties of Rear Contact CIGS Solar CellsPublication . Cunha, Jose M. V.; Fernandes, P. A.; Salome, Pedro M. P.; Lopes, Tomas S.; Bose, Sourav; Hultqvist, Adam; Chen, Wei-Chao; Donzel-Gargand, Olivier; Ribeiro, Rodrigo M.; Oliveira, Antonio J. N.; Edoff, MarikaA novel architecture that comprises rear interface passivation and increased rear optical reflection is presented with the following advantages: i) enhanced optical reflection is achieved by the deposition of a metallic layer over the Mo rear contact; ii) improved interface quality with CIGS by adding a sputtered Al 2 O 3 layer over the metallic layer; and, iii) optimal ohmic electrical contact ensured by rear-openings refilling with a second layer of Mo as generally observed from the growth of CIGS on Mo. Hence, a decoupling between the electrical function and the optical purpose of the rear substrate is achieved. We present in detail the manufacturing procedure of such type of architecture together with its benefits and caveats. A preliminary analysis showing an architecture proof-of-concept is presented and discussed.
- A Deep Learning Approach for PV Failure Mode Detection in Infrared Images: First InsightsPublication . Rocha, Daniel; Lopes, Miguel; Teixeira, Jennifer P.; Fernandes, Paulo A.; Morais, Modesto; Salome, Pedro M. P.Large-scale solar power plants require cheap and quick inspections, for this unmanned aerial vehicle (UAV's) for high resolution optical and infrared imaging were introduced in the past years. While using UAV’s is fast for image acquisition, image is a time-consuming process where the best of practice today is still for an expert to individually analyze each image. As such, in this work we use computer vision to accelerate this process. We performed an instance segmentation assessment using a pretrained mask R-CNN for the segmentation of defective modules, and cells, as well as for segmentation and classification of failures. This method was chosen due its good past performance. In this work we created a database from a solar power plant consisting of 42048 modules and an expert analyzed the images. Later on, our computer algorithm results were benchmarked against the expert. Our algorithm achieved a mean average precision (mAP) in defective module segmentation mask of 72.1 % and 47.9 % in segmentation mask of failure type with an intersection over union threshold (IoU) of 0.50, without human interference. The presented preliminary results allow to assess the methodology advantages and drawbacks to increase performance and pave the way to a large-scale study.
- Multidefect detection tool for large-scale PV plants: Segmentation and classificationPublication . Rocha, Daniel; Alves, Joao; Lopes, Vitor; Teixeira, Jennifer P.; Fernandes, Paulo A.; Costa, Mauro; Morais, Modesto; Salome, Pedro M. P.Unmanned aerial vehicles (UAVs) with highresolution optical and infrared (IR) imaging have been introduced in recent years to perform inexpensive and fast inspections in operation and maintenance activities of solar power plants, reducing the labor needed, while lowering the on-site inspection time. Even though UAVs can acquire images extremely quickly, the analysis of those images is still a time-consuming procedure that should be performed by a trained professional. Therefore, a computer vision approach may be used to accelerate image analysis. In this work, a dataset of IR images was created from a 10-MW solar power plant and a comparative analysis between mask R- convolutional neural network (CNN) and U-Net was performed for two experiments. Concerning the defective module segmentation, the mask R-CNN algorithm achieved a mean average precision at intersection over union (IoU) = 0.50 of 0.96, using augmentation data. Regarding the segmentation and classification of failure type, the algorithm reached a value of 0.88 considering the same evaluation metric and data augmentation.When compared to the U-Net in terms of IoU, the mask R-CNN outperformed it with 0.87 and 0.83 for the first and second experiments, respectively.
- Rear Optical Reflection and Passivation Using a Nanopatterned Metal/Dielectric Structure in Thin-Film Solar CellsPublication . Lopes, Tomas S.; Cunha, Jose M. V.; Bose, Sourav; Barbosa, Joao R. S.; Borme, Jerome; Donzel-Gargand, Olivier; Rocha, Celia; Silva, Ricardo; Hultqvist, Adam; Chen, Wei-Chao; Silva, Ana G.; Edoff, Marika; Fernandes, P. A.; Salome, Pedro M. P.Currently, one of the main limitations in ultrathin Cu(In,Ga)Se 2 (CIGS) solar cells are the optical losses, since the absorber layer is thinner than the light optical path. Hence,light management, including rear optical reflection, and light trapping is needed. In this paper, we focus on increasing the rear optical reflection. For this, a novel structure based on having a metal interlayer in between the Mo rear contact and the rear passivation layer is presented. In total, eight different metallic interlayers are compared. For the whole series, the passivation layer is aluminum oxide (Al 2 O 3 ). The interlayers are used to enhance the reflectivity of the rear contact and thereby increasing the amount of light reflected back into the absorber. In order to understand the effects of the interlayer in the solar cell performance both from optical and/or electrical point of view, optical simulations were performed together with fabrication and electrical measurements. Optical simulations results are compared with current density-voltage (J-V) behavior and external quantum efficiency measurements. A detailed comparison between all the interlayers is done, in order to identify the material with the greatest potential to be used as a rear reflective layer for ultrathin CIGS solar cells and to establish fabrication challenges. The Ti-W alloy is a promising a rear reflective layer since it provides solar cells with light to power conversion efficiency values of 9.9%, which is 2.2% (abs) higher than the passivated ultrathin sample and 3.7% (abs) higher than the unpassivated ultrathin reference sample.
- SiOx Patterned Based Substrates Implemented in Cu(In,Ga)Se2 Ultrathin Solar Cells: Optimum ThicknessPublication . Oliveira, Kevin; Teixeira, Jennifer P.; Chen, Wei-Chao; Lontchi Jioleo, Jackson; Oliveira, Antonio J. N.; Caha, Ihsan; Francis, Leonard Deepak; Flandre, Denis; Edoff, Marika; Fernandes, Paulo A.; Salome, Pedro M. P.Interface recombination in sub-µm optoelectronics has a major detrimental impact on devices’ performance, showing the need for tailored passivation strategies to reach a technological boost. In this work, SiOx passivation based substrates were developed and integrated into ultrathin Cu(In,Ga)Se2 (CIGS) solar cells. This study aims to understand the impact of a passivation strategy, which uses several SiOx layer thicknesses (3, 8, and 25 nm) integrated into high performance substrates (HPS). The experimental study is complemented with 3D Lumerical finite-difference time-domain (FDTD) and 2D Silvaco ATLAS optical and electrical simulations, respectively, to perform a decoupling of optical and electronic gains, allowing for a deep discussion on the impact of the SiOx layer thickness in the CIGS solar cell performance. This study shows that as the passivation layer thickness increases, a rise in parasitic losses is observed. Hence, a balance between beneficial passivation and optical effects with harmful architectural constraints defines a threshold thickness to attain the best solar cell performance. Analyzing their electrical parameters, the 8 nm novel SiOx based substrate achieved a light to power conversion efficiency value of 13.2 %, a 1.3 % absolute improvement over the conventional Mo substrate (without SiOx).
- Understanding the AC Equivalent Circuit Response of Ultrathin Cu(In,Ga)Se2 Solar CellsPublication . Cunha, Jose M.V.; Rocha, Celia; Vinhais, Carlos; Fernandes, P. A.; Salome, Pedro M. P.This paper aims to study the ac electrical response of standard-thick, ultrathin, and passivated ultrathin Cu(In,Ga)Se 2 (CIGS) solar cells. Ultrathin CIGS is desired to reduce production costs of CIGS solar cells. Equivalent circuits for modeling the behavior of each type of solar cells in ac regime are based on admittance measurements. It is of the utmost importance to understand the ac electrical behavior of each device, as the electrical behavior of ultrathin and passivated ultrathin CIGS devices is yet to be fully understood. The analysis shows a simpler ac equivalent circuit for the ultrathin device without passivation layer, which might be explained by the lowered bulk recombination for thin-film CIGS solar cells when compared with reference thick ones. Moreover, it is observed an increase in shunt resistance for the passivated ultrathin device, which strengthens the importance of passivation for shunts mitigation when compared with unpassivated devices.
- Voids in Kesterites and the Influence of Lamellae Preparation by Focused Ion Beam for Transmission Electron Microscopy AnalysesPublication . Ribeiro-Andrade, Rodrigo; Sahayaraj, Sylvester; Vermang, Bart; Correia, M. Rosario; Sadewasser, Sascha; Gonzalez, Juan Carlos; Fernandes, P. A.; Salome, Pedro M. P.Kesterite solar cells based on Cu 2 ZnSnS 4 and Cu 2 ZnSnSe 4 (CZTSe) are potential future candidates to be used in thin-film solar cells. The technology still has to be developed to a great extent and for this to happen, high levels of confidence in the characterization methods are required, so that improvements can be made on solid interpretations. In this study, we show that the interpretations of one of the most used characterization techniques in kesterites, scanning transmission electron microscopy (STEM), might be affected by its specimen preparation when using focused ion beam (FIB). Using complementary measurements based on scanning electron microscopy and Raman scattering spectroscopy, compelling evidence shows that secondary phases of ZnSe mixed in the bulk of CZTSe are the likely cause of the appearance of voids in STEM lamellae. Sputtering simulations support this interpretation by showing that Zn in a ZnSe matrix is preferentially sputtered compared with any metal atom in a CZTSe matrix.