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Silicon surface passivation with atomic layer deposited (ALD) thin films has gained more and more interest in the PV community in recent years. With ALD good film quality, accurate thickness control and conformity are reached. Furthermore, ALD is capable of coating difficult substrates such as nanostructured surfaces with the same accuracy as flat surfaces. A variety of materials such as Al2O3, TiO2 and HfO2 demonstrate good surface passivation quality both for front and rear surface of silicon solar cells. In addition of providing good surface passivation, thin films with high refractive index e.g. HfO2, TiO2 and AlN can act simultaneously as antireflection coatings when applied on the front surface of the device. Hence, ALD thin films can reduce both electrical and reflective losses in solar cells.
Thorough investigation of the optical properties of these layers is crucial for several reasons related to their production and use. Optical measurements provide a fast, easy, non-destructive, and in situ capable approach to quality assurance for photovoltaic devices. As the function of the final device is optical, optimisation of the device performance relies strongly on the knowledge of the wide-range dielectric function of the thin layers. In this contribution, we determined the optical constants of ALD generated layers of AlN, Al2O3, TiO2, and HfO2 in a wide spectral range covering the near ultraviolet and the mid-infrared regions by means of spectroscopic ellipsometry. By combining data from a UV-Vis-NIR ellipsometer (Woollam M2000DI) and an FTIR ellipsometer (Sentech Sendira), we can determine the optical constants alongside with the layer thicknesses from one large set of spectroscopic measurements. We consider this a contribution to the metrological treatment of stratified and structured thin films in the optical range by polarisation-sensitive measurement methods.
A sustainable recycling of photovoltaic (PV) thin film modules gains in importance due to the considerable growing of the PV market and the increasing scarcity of the resources for semiconductor materials. The paper presents the development of two strategies for thin film PV recycling based on (wet) mechanical processing for broken modules, and combined thermal and mechanical methods for end-of-life modules. The feasibility of the processing steps was demonstrated in laboratory scale as well as in semi-technical scale using the example of CdTe and CIS modules. Pre-concentrated valuables In and Te from wet mechanical processing can be purified to the appropriate grade for the production of new modules.
An advantage of the wet mechanical processing in comparison to the conventional procedure might be the usage of no or a small amount of chemicals during the several steps.
Some measures are necessary in order to increase the efficiency of the wet mechanical processing regarding the improvement of the valuable yield and the related enrichment of the semiconductor material.
The investigation of the environmental impacts of both recycling strategies indicates that the strategy, which includes wet mechanical separation, has clear advantages in comparison to the thermal treatment or disposal on landfills.
Optical and thermal analysis of PVB encapsulant polymer functionalized with luminescent organic dyes
(2018)
This work focused on the technology of luminescent down shift (LDS), with a primary aim to identify and investigate a methodology to introduce the luminescent organic dye into PVB polymer encapsulant as emergent material for photovoltaic application. For this goal, we propose to study the feasibility to implement the LDS functionality and to identify suitability of available luminescent to be incorporated into the host polymer encapsulant material. The first step to this direction was through a comprehensive optical study of Violet 570 (V) organic dye in ethanol solvent. The methodology and experimental conditions such as laboratory polymer preparation and luminescence dye concentration were presented. Also, the emergent polymer encapsulant sheets were characterized by using optical and thermal analysis techniques. The absorption spectrum of the prepared PVB material shifts towards longer wavelengths, with increasing organic dye concentration.