Surface Roughness and Geometric Features of Photovoltaics

Optimizing the energy absorption of a solar cell is important for the survival of the technology as a renewable resource. The numerous layers of coating and glass protection enable the absorption, transmittance, and reflection of light which is needed for the photovoltaic cells to work. As most consumer solar cells perform at 15-18 % efficiency, maximizing their energy output is a challenge.

Importance of Solar Panel Testing

Studies have determined that surface roughness plays a key role in the reflectance of light. The initial layer of glass has to be as smooth as it can be to mitigate reflectance of light, but the subsequent layers do not adhere to this rule.

At each coatings interface to another, some roughness is needed to heighten the probability of light scattering within their respective depletion zones and heighten the absorption of light within the cell. Enhancing the surface roughness in these locations enables the solar cell to perform to the best of its ability. Measuring surface roughness can be done accurately and quickly using the Nanovea HS2000 High Speed Sensor.

Measurement Objectives

The capabilities of the Nanovea HS2000 High Speed Sensor will be shown in this study by measuring the geometric features and surface roughness of a photovoltaic cell. For this study, a monocrystalline solar cell with no glass protection will be measured but the technique can be employed for a number of other applications.

Solar Cell sample on Nanovea HS2000L Prolometer.

Solar Cell sample on Nanovea HS2000L Prolometer.

The below test parameters were utilized to measure the surface of the solar cell:

Table 1: Test parameters used.

Solar Cell
Optical Pen L1
Acquisition rate 100 pps
Averaging 1
Measured surface 30 mm x 10 mm
Step size 5 μm x 5 μm
Measurement Time (h:m:s) 00:13:43

Sample of solar cell analyzed.

Sample of solar cell analyzed.

Results and Discussion

The 2D false color view of the solar cell and an area extraction of the surface with its respective height parameters is shown below. A gaussian filter was applied to both surfaces and a more aggressive index was employed in order to flatten the extracted area.

False color view of the photovoltaic cell

Figure 1: False color view of the photovoltaic cell (Top)

Figure 2: False color view of the photovoltaic cell (Bottom)

Surface roughness of the first layer of the photovoltaic surface.

Figure 3: Surface roughness of the first layer of the photovoltaic surface.

3D view of the first layer of the photovoltaic surface.

Figure 4: 3D view of the first layer of the photovoltaic surface.

Profile roughness amplitude parameters of the first layer of the photovoltaic surface.

Figure 5: Profile roughness amplitude parameters of the first layer of the photovoltaic surface.

This eliminates form (or waviness) bigger than the cut-off index, leaving behind features which show the roughness of the solar cell. To measure their geometric characteristics, a profile was taken perpendicular to the orientation of the gridlines, which can be observed below. The gridline width, pitch, and step height, can be calculated for any specific place on the solar cell.

Width measurement of the gridline.

Figure 6: Width measurement of the gridline.

Pitch measurement of the gridline.

Figure 7: Pitch measurement of the gridline.

Step height measurement of the gridline.

Figure 8: Step height measurement of the gridline.

Conclusion

The Nanovea HS2000 Line Sensor’s ability to measure a monocrystalline photovoltaic cell’s surface roughness and features was shown in this study. The Nanovea HS2000 Line Sensor is a perfect choice for quality control inspections, due to its capability to automate accurate measurements of numerous samples and set pass fail limits.

Reference

  1. Scholtz, Lubomir. Ladanyi, Libor. Mullerova, Jarmila. “Influence of Surface Roughness on Optical Characteristics of Multilayer Solar Cells “ Advances in Electrical and Electronic Engineering, vol. 12, no. 6, 2014, pp. 631-638.

This information has been sourced, reviewed and adapted from materials provided by Nanovea.

For more information on this source, please visit Nanovea.

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