Volume Holographic Optical Elements (HOEs) present interesting characteristics for photovoltaic applications as they can select spectrum for concentrating the target bandwidth and avoiding non-desired wavelengths, which can cause the decrease of the performance on the cell, for instance by overheating it. Volume HOEs have been recorded on Bayfol HX photopolymer to test the suitability of this material for solar concentrating photovoltaic systems. The HOEs were recorded at 532 nm and provided a dynamic range, reaching close to 100% efficiency at 800 nm. The diffracted spectrum had a FWHM of 230 nm when illuminating at Bragg angle. These characteristics prove HOEs recorded on Bayfol HX photopolymer are suitable for concentrating solar light onto photovoltaic cells sensitive to that wavelength range.

A ray tracing algorithm is developed to analyze the energy performance of transmission and phase volume holographic lenses that operate with broadband illumination. The agreement between the experimental data and the theoretical treatment has been tested. The model has been applied to analyze the optimum recording geometry for solar concentration applications.

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Concentrating photovoltaics for building integration can be successfully carried out with Holographic Optical Elements (HOEs) because of their behavior analogous to refractive optical elements and their tuning ability to the spectral range that the photovoltaic (PV) cell is sensitive to. That way, concentration of spectral ranges that would cause overheating of the cell is avoided. Volume HOEs are usually chosen because they provide high efficiencies. However, their chromatic selectivity is also very high, and only a small part of the desired spectral range reaches the PV cell. A novel approach is theoretically and experimentally explored to overcome this problem: the use of HOEs operating in the transition regime, which yield lower chromatic selectivity while keeping rather high efficiencies. A model that considers the recording material’s response, by determining the index modulation reached for each spatial frequency and exposure dosage, has been developed. It has been validated with experimental measurements of three cylindrical holographic lenses with different spatial frequency ranges recorded in Bayfol HX photopolymer. Simulations of systems comprising two lenses and a mono-c Si PV cell are carried out with the standard AM 1.5D solar spectrum. Promising results are obtained when using the system with lower spatial frequencies lenses: a total current intensity equal to 3.72 times the one that would be reached without the concentrator.

A novel stacking procedure is presented for volume phase holographic gratings (VPHGs) recorded in photopolymer material using Corning Willow Glass as a flexible substrate in order to achieve broader angular and spectral selectivity in a diffractive device with high efficiency for solar and LED applications. For the first time to our knowledge, we have shown a device designed for use with a white LED that has the same input and output angles and high efficiency when illuminated by different wavelengths. In this paper, two VPHGs were designed, experimentally recorded, and tested when illuminated at normal incidence. The experimental approach is based on stacking two individual gratings in which the spatial frequency and slant have been tailored to the target wavelength and using real-time on-Bragg monitoring of the gratings in order to control the recorded refractive index modulation, thereby optimizing each grating efficiency for its design wavelength. Lamination of the two gratings together was enabled by using a flexible glass substrate (Corning Willow Glass). Recording conditions were studied in order to minimize the change in diffraction efficiency and peak diffraction angle during lamination and bleaching. The final fabricated stacked device was illuminated by a white light source, and its output was spectrally analyzed. Compared to a single grating, the stacked device demonstrated a twofold increase in angular and wavelength range. The angular and wavelength selectivity curves are in good agreement with the theoretical prediction for this design. This approach could be used to fabricate stacked lenses for white light LED or solar applications.