Photovoltaics Testing

Lucas, Mariana Mar, et al. Journal of Alloys and Compounds 887 (2021): 161364.

The structural characterization of individual grains in thin-film photovoltaics is critical for understanding the performance of polycrystalline solar cell materials. This study utilizes three-dimensional X-ray diffraction (3DXRD) to investigate the microstructure of Cu₂ZnSnS₄ (CZTS) absorbers, focusing on phase identification, grain size, orientation, strain distribution, and twin boundaries. The method enables non-destructive analysis of complex materials, distinguishing between phases with similar lattice parameters, such as CZTS and ZnS.

Through this technique, nearly 600 grains in CZTS were examined, revealing a 2.5% fraction of the ZnS secondary phase. The strain distribution indicated average tensile stress (~70 MPa) within the film plane and compressive stress (~145 MPa) normal to the film. Notably, 41% of the grains were identified as Σ3 twins, with the 180° rotation along the<221>axis being the most frequent boundary type.

The 3DXRD approach provides crucial insights into the microstructure that directly influence the photovoltaic properties, such as strain-induced bandgap variations and the role of twin boundaries in charge transport mechanisms. This detailed understanding of the microstructure can guide the design of more efficient CZTS-based solar cells by optimizing the grain-level properties for improved photovoltaic performance.

Block, Alejandro Borja, et al. Solar Energy 267 (2024): 112227.

Accurate color characterization is crucial for the manufacturing quality control and long-term stability assessment of building-integrated photovoltaic (BIPV) products. Traditional colorimetric techniques face significant challenges when measuring colors under transparent layers like solar PV laminates. This study introduces an innovative large area illumination (LAI) colorimeter, combining a fiber optic spectrometer and large area illumination, to overcome these limitations. The proposed colorimeter was compared to common scanners, portable commercial colorimeters, and integrated sphere spectrometers.

The results reveal that traditional scanners produce darker images due to light losses in the glass, leading to inaccurate color determination. As glass thickness increases, common devices show decreased reflectance, particularly for high-reflective foils. In contrast, the LAI colorimeter demonstrates minimal signal reduction, providing more accurate color measurements even under thick glass laminates. For example, it significantly reduces the color change from 57 (using a commercial colorimeter) to only 3 for ivory-colored glass.

This research demonstrates that the LAI colorimeter effectively compensates for light losses and provides reliable color characterization, offering substantial improvements in BIPV manufacturing and quality control. The tool's potential applications extend beyond photovoltaics, potentially benefiting industries such as glass, construction, and automotive. Future work should focus on further improving the LAI colorimeter's portability and calibration, ensuring its applicability in commercial PV modules.

Benali, Hajar, et al. Materials today: Proceedings (2024).

The incorporation of aluminum into zinc oxide (ZnO) films enhances their potential for use as transparent conducting oxides in photovoltaic cells. This study investigates the effects of varying aluminum doping concentrations (0 to 10 at.%) on the structural and optical properties of ZnO thin films, deposited via the sol–gel dip-coating method. X-ray diffraction (XRD) analysis confirms the formation of the desired hexagonal wurtzite crystal structure, with a preferential orientation along the (0 0 2) direction. As aluminum doping increases, the crystallite size decreases from 22 nm to 19 nm, indicating the successful substitution of Zn²⁺ ions by Al³⁺ ions within the lattice.

Optical measurements using UV-visible spectroscopy show that aluminum doping improves the transparency of the films, with transmittance ranging from 60% to 79% in the 350-750 nm range. The band gap slightly widens with increased Al concentration, fluctuating between 3.21 and 3.25 eV, without significant impact on the refractive index or extinction coefficient. Notably, the optical properties approach their peak values at 10 at.% Al, suggesting enhanced performance for solar cell applications. These results demonstrate the promising potential of aluminum-doped ZnO thin films for use in photovoltaic devices, with further investigation needed to optimize their performance for practical applications in solar energy harvesting.