Elusive Solar Light-Trapping Limit Nearly Reached
DELFT, Netherlands, Feb. 27, 2014 — The theoretical limit of light-trapping in solar cells has eluded
researchers for decades. But a group from Delft University of Technology
(TU Delft) has come closer to it than anyone else.
researchers, members of TU Delft’s Photovoltaic Materials and Devices
(PVMD) group, have experimentally demonstrated the theoretical limit of
the enhancement of light absorption using an advanced metal-free
light-trapping scheme for the ultrathin crystalline silicon wafers that
A 20-µm-thick flexible absorber extracted from the crystalline silicon
wafer support. Photos courtesy of TU Delft (Photovoltaic Materials and
On the front of the silicon wafers, they applied a nanotexture known as
black silicon. On the back, they implemented a random pyramidal texture
coated with a photonic dielectric back reflector, designed to exhibit
maximal and omnidirectional internal reflectance.
Wafers thinner than 35 µm allowed the group to achieve more than 99
percent of the theoretical classical light absorption limit in the 400-
to 1200-nm spectral range (with the photonic reflector), and up to 99.8
percent with the silver back reflector.
implementation of the light-trapping scheme in crystalline silicon
solar cells required an adequate surface passivation of the front
Cross-sectional scanning electron microscopy image of optimized
dielectric distributed Bragg reflector coating randomly-etched pyramids
of crystalline silicon.
For this purpose, the researchers also developed thermal silicon oxide and aluminum oxide passivation layers.
These developments essentially pave the way for the next generation of
high-efficiency, cost-effective ultrathin crystalline silicon solar
cells, the researchers said.
The work was funded by Agentschap NL, with project partners Solland
Solar Cells and the Energy Research Centre of the Netherlands. The
research is published in ACS Photonics (doi: 10.1021/ph4001586).
- The ratio of reflected flux to incident flux. Unless otherwise specified, the total reflectance is meant; it is sometimes convenient to divide this into the sum of the specular and the diffuse reflectance.
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