This study presents improved regular inverted pyramid structures, which should act as photonic crystals and thus are expected to highly increase light absorption. The prepared structures exhibit light trapping en par with random pyramid textured surfaces, but not as expected above. Thus, applying these structures to IBC solar cells does not lead to a higher short circuit current density.
In this work we present an optimized process for the photolithographic fabrication of inverted pyramid photonic crystals (PC) with 3.1 µm periodicity on Si(001)-substrates to improve the light trapping in single junction solar cells. Anisotropic alkaline etch was used to form the pyramids with (111)-sidewalls using partial surface masking with lithographically structured SiO2. Ridge widths between the pyramids down to (150 ± 50) nm were achieved, while ensuring a yield of multiple (2 × 2) cm2 areas per wafer sample. After deposition of an antireflection stack consisting of AlO
x
, SiN
y
, and SiO
z
with different thickness optimizations a weighted reflection approaching that of a random pyramid reference sample could be shown. We demonstrate a path length enhancement of 25 at a wavelength of 1200 nm for our cell with PCs. This is en par with but not superior to the respective value for the reference sample with random pyramids, and still below the Lambertian limit. Furthermore, we present the first POLO2-IBC (interdigitated back contact) solar cells with such photonic crystals on the front sides. These solar cells feature a power conversion efficiency of 22.9%.
Solar RRL, Volume 9, Issue 22, November 2025. Read More
