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38th European Photovoltaic Solar Energy Conference and Exhibition; 330-333, Silicon heterojunction (HJ) solar cell is one of the leading technologies for single junction photovoltaic devices and it could be successfully integrated into a silicon based multijunction solar device, in conjunction with a large band gap cell. To be used as a bottom cell, the HJ device needs to adapt to the current technology for top cells, which are typically far less mature and characterized by smaller areas. However, if the HJ device is cut from a finished larger cell, the original edge passivation gets lost, causing the introduction of surface recombination paths and an overall decrease of the device performance. In this context, the development of a proper edge passivation procedure to be applied to high quality HJ solar cells becomes of major importance. We tried two different strategies of edge passivation based either on wet processes, such as the mesa etching of the device, or plasma treatment of the vertical edges. The latter consisting in the deposition of 1-10 nm of hydrogenated amorphous Si on the edges. In order to characterize the recombination losses and quantify the effect of different passivations, we did current-voltage measurements in light and dark conditions and quasi- steady-state photoconductivity measurements.

38th European Photovoltaic Solar Energy Conference and Exhibition; 501-504, Silicon heterojunctions (Si HJs) are regarded as a promising structure to develop high efficiency tandem solar cells. However, the Si HJ structure has been optimized for use as single junction device and variations might be made in order to adapt it to tandem applications. In this work we analyse by optical simulations the improvements that could be achieved in the short circuit current of Si HJs used as bottom cell in tandem devices, if the front TCO layer is made thicker. This solution allows to adapt the absorption in the Si HJ to the incident light spectrum, that is rich of high wavelength photons if a wide band gap cell is put on top of the Si HJ. The investigation has been carried out for two top cell technologies: a high efficiency InGaP solar cell and a semitransparent perovskite solar cell. The improvement in JSC is of the order of 1 mA in both cases, and is more pronounced when the edge of transparency of the top cell occurs at higher wavelength.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 66-68, In this article, we demonstrate a patch, which contains upconverting crystals of Gd2O2S:Yb3+, Er3+ mixed with a UV curable gel, integrated with a textured back-reflector that can be externally affixed to a bifacial thin-film silicon solar cell. The patch serves to provide the benefit of light trapping as well as spectrum upconversion to the solar cell fabricated on a flat substrate. Upconverting patches with different textures were studied for their effectiveness in enhancing the short-circuit current density of the solar cell and for the relationship between the current enhancement and the intensity of the incident light. The upconverting patch is shown to enhance the solar cell performance and offers a new stick-on technique to apply upconversion-based strategies to existing solar cells. The photogenerated short-circuit current densities of the solar cell show a power-law dependence on the illuminated laser light intensity when an upconverter patch is attached to the solar cell (exponent 1.5-1.6) while a linear dependence is observed for the solar cell without the upconverter patch.

26th European Photovoltaic Solar Energy Conference and Exhibition; 22-27, We present an overview of the project NASCEnT and the first results we were able to achieve after one year of project duration. The overall objective of the project is to develop new nano-materials with new production technologies and to fabricate silicon quantum dot (Si QD) materials for all-silicon tandem solar cells to achieve increased efficiencies. The understanding of electrical transport and recombination mechanisms in these newly developed nano-materials will enable us to design novel solar cell structures that help to overcome the efficiency limits of conventional solar cell concepts. So far we developed simple device structures and process sequences for both material systems (Si QDs in silicon oxide and silicon carbide) and tested a pin solar cell structure. Another objective of the project is to ensure the compatibility of the newly developed technologies with high-throughput processing leading to further cost-reduction. Within the scope of this project the novel concept of band gap-tuneable quantum dot superlattices is to be exploited in combination with a wafer-based high efficiency silicon solar cell as well as with a thin-film solar cell structure. The outcome of the project will be significant progress in solar cell evolution and will lead to higher efficiencies for solar cells and to ongoing cost-reductions from both a short-term and a long-term perspective.

26th European Photovoltaic Solar Energy Conference and Exhibition; 361-366, Aim of this work is the determination of the optical parameters of silicon nanocrystals (nc-Si) in Silicon Rich Carbide (SRC) matrix and in particular of the absorption coefficient of the material, essential in the design of photovoltaic devices. The nanocrystals were formed using the superlattice SRC/SiC approach followed by annealing. The optical properties of the superlattices after annealing up to 1100 °C are investigated. Severe shrinkage of the materials is observed, more marked for higher carbon concentration. Contrary to the case of Silicon Rich Oxide (SRO) matrix, the simulation of R&T spectra based on EMA modeling shows that the material can be described by a mixture of crystallized SiC, crystallized Si, and amorphous Si. Larger Si concentration in the SRC layer leads to larger crystallized fraction. The differences with the SRO case are illustrated and discussed. The results are applied to the optical simulation of a hypothetical tandem device. It is obtained that much thinner absorbers could be used in the SRC case with respect to SRO one.