STABILITY OF BLACK INTERCONNECT COATINGS FOR SOLAR PHOTOVOL-TAIC MODULE APPLICATIONS

Aesthetics is crucial in the development of Building Integrated Photovoltaic (BIPV) products. Manufacturers strive to mask, typically through expensive manual processes, the reflective metallic interconnects to obtain uniform module colors. Inks offer an automated alternative but must be implemented in the production line and remain stable, maintaining their appearance over time. In this study, three black metallic ribbons were tested: one commercially pre-coated and two coated with UV-curable inkjet printing. Accelerated UV-light exposure was applied according to IEC standards on coupons mimicking glass/backsheet (G/Bs) samples including encapsulant with and without UV blockers. Additionally, one-cell modules with ink-coated ribbons were fabricated using a laboratory-designed automatic inkjet printer and exposed to accelerated UV ageing. Results showed that the commercially available coated ribbon remained stable after 120 kWh/m2 of UV exposure. However, UV-curable inkjet inks caused color changes in the encapsulant around metallic interconnects, regardless of the encapsulant used or the presence or not of UV blockers in the encapsulant. Ink #1 exhibited the most color change under UV-dose. Its main component, 2-phenoexyethyl-acrylate (2-PEA), photodegraded and caused yellowing. An early sign of degradation with a slight increase of 22% in carbonyl index (CI) was observed after 15 kWh/m2 of UV exposure. Encapsulants with UV blockers successfully mitigated 2-PEA photodegradation on G/BS laminates; however, color change occurred with ink #1 despite their application. Using this ink on PV modules results in color change, but the electrical performance remains relatively stable, with less than a 3% power loss after 360 kWh/m2 of UV exposure

In-situ formation of magnesium silicide nanoparticles on the surface of the hydrogenated silicon films

The magnesium silicide nanoparticles were formed on the surface of hydrogenated silicon thin films by thermal evaporation, annealing and hydrogen plasma treatment. The high reactivity of silicon and magnesium leads to the self-formation of magnesium silicide nanoparticles (NPs). The reaction is stimulated in-situ by the low pressure hydrogen plasma. The presence of Mg2Si NPs was confirmed by SEM and Raman spectroscopy. The photothermal deflection spectroscopy (PDS) shows the enhanced optical absorption in the near infrared spectrum. The diode structures with insitu embedded Mg2Si NPs were characterized by the volt-ampere measurements in dark and under AM1.5 spectrum

Impact of AFM-induced nano-pits in a-Si:H films on silicon crystal growth

Conductive tips in atomic force microscopy (AFM) can be used to localize field-enhanced metal-induced solid-phase crystallization (FE-MISPC) of amorphous silicon (a-Si:H) at room temperature down to nanoscale dimensions. In this article, the authors show that such local modifications can be used to selectively induce further localized growth of silicon nanocrystals. First, a-Si:H films by plasma-enhanced chemical vapor deposition on nickel/glass substrates are prepared. After the FE-MISPC process, yielding both conductive and non-conductive nano-pits in the films, the second silicon layer at the boundary condition of amorphous and microcrystalline growth is deposited. Comparing AFM morphology and current-sensing AFM data on the first and second layers, it is observed that the second deposition changes the morphology and increases the local conductivity of FE-MISPC-induced pits by up to an order of magnitude irrespective of their prior conductivity. This is attributed to the silicon nanocrystals (<100 nm) that tend to nucleate and grow inside the pits. This is also supported by micro-Raman spectroscopy

Synthesis, structure, and opto-electronic properties of organic-based nanoscale heterojunctions

Enormous research effort has been put into optimizing organic-based opto-electronic systems for efficient generation of free charge carriers. This optimization is mainly due to typically high dissociation energy (0.1-1 eV) and short diffusion length (10 nm) of excitons in organic materials. Inherently, interplay of microscopic structural, chemical, and opto-electronic properties plays crucial role. We show that employing and combining advanced scanning probe techniques can provide us significant insight into the correlation of these properties. By adjusting parameters of contact- and tapping-mode atomic force microscopy (AFM), we perform morphologic and mechanical characterizations (nanoshaving) of organic layers, measure their electrical conductivity by current-sensing AFM, and deduce work functions and surface photovoltage (SPV) effects by Kelvin force microscopy using high spatial resolution. These data are further correlated with local material composition detected using micro-Raman spectroscopy and with other electronic transport data. We demonstrate benefits of this multi-dimensional characterizations on (i) bulk heterojunction of fully organic composite films, indicating differences in blend quality and component segregation leading to local shunts of photovoltaic cell, and (ii) thin-film heterojunction of polypyrrole (PPy) electropolymerized on hydrogen-terminated diamond, indicating covalent bonding and transfer of charge carriers from PPy to diamond

Guided assembly of nanoparticles on electrostatically charged nanocrystalline diamond thin films

We apply atomic force microscope for local electrostatic charging of oxygen-terminated nanocrystalline diamond (NCD) thin films deposited on silicon, to induce electrostatically driven self-assembly of colloidal alumina nanoparticles into micro-patterns. Considering possible capacitive, sp2 phase and spatial uniformity factors to charging, we employ films with sub-100 nm thickness and about 60% relative sp2 phase content, probe the spatial material uniformity by Raman and electron microscopy, and repeat experiments at various positions. We demonstrate that electrostatic potential contrast on the NCD films varies between 0.1 and 1.2 V and that the contrast of more than ±1 V (as detected by Kelvin force microscopy) is able to induce self-assembly of the nanoparticles via coulombic and polarization forces. This opens prospects for applications of diamond and its unique set of properties in self-assembly of nano-devices and nano-systems

Optoelectronic and structural properties of thin silicon films

Matematicko-fyzikální fakultaFaculty of Mathematics and Physic

Effect of excitation wavelength on the measurement and interpretation of the Raman spectra of the silicon thin films

We discussed effect of wavelength of used excitation laser on the measurement and interpretation of the Raman spectra