Wavelength and angle resolved reflectance measurements of pyramidal textures for crystalline silicon photovoltaics

Abstract

Wavelength and angle resolved scattering (WARS) reflectance measurements are attractive to the photovoltaic (PV) industry as a means of characterizing the lighttrapping properties of a textured front surface. Moreover, at the PV module level, where a stack comprising encapsulants and glass is present, large angle scattering can promote total internal reflection at the interfaces and redirect light back towards the solar cell, thus increasing the photocurrent of the device. In this work, we present WARS measurements of a potassium hydroxide (KOH)etched random pyramid surface in the 6-90 range and identify the main paths the photons experience through reflections from various facets of the pyramids. Our results, combined with raytracing predictions, show that a reassessment of the morphology for simulation inputs is advised for a more comprehensive description of the experimental light paths due to a distribution of power across multiple scattering angles and a lower average pyramid base angle. In addition, we discuss the implications on the total amount of light trapped at the glass-air interface and show that for a typical encapsulant refractive index of 1.5, approximately 14.5% of the scattered light is predicted to be trapped by the fabricated pyramidal texture. This is a significant increase over the 3.8% calculated to be trapped when assuming a dihedral base angle fixed to 54.74 .

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“…Measurements from SEM images [see Fig. 3(b)] suggest that the actual achieved angle between wafer surface and trench wall is slightly smaller than the angle between the (100) and (111) planes, in line with recent investigation of scattering angles of pyramidal Si surfaces [32].…”

Determining the optical properties of solar cells using low cost scanners

“…The variation in reflection comes from the pyramid coverage, and the ability for the light to be reflected off one pyramid and onto another. The resulting scattering profile has strong features relating to the geometry of the pyramids 10 .…”

Influence of WO3-Based Antireflection Coatings on Current Density in Silicon Heterojunction Solar Cells

“…The surface morphology of the c-Si substrate was set to random upright pyramids. The angle of the upright pyramid was set to 54.74 • , which is typical for solar cells with a surface textured with a tetramethylammonium hydroxide (TMAH) solution [35]. The planar fraction was set to 0%.…”