# Re-defining Non-tracking Solar Cell Efficiency Limits with Directional Spectral Filters

## TL;DR

Directional spectral filters can boost the efficiency of non-tracking solar cells and stabilize their energy output.

## Contribution

The paper introduces a new method to increase non-tracking solar cell efficiency using directional spectral filters.

## Key findings

- Directional spectral filters can increase non-tracking solar cell efficiency by up to 0.5% at the equator.
- These filters can reduce the absorber layer thickness by up to 40%.
- Filters can regulate solar cell energy output over a day or year.

## Abstract

Optical filters that respond to the wavelength and direction
of
incident light can be used to increase the efficiency of tracking
solar cells. However, as tracking solar cells are more expensive to
install and maintain, it is likely that nontracking solar cells will
remain the main product of the (terrestrial) solar cell industry.
Here we demonstrate that directional spectral filters can also be
used to increase the efficiency limit of nontracking solar cells at
the equator beyond what is currently understood by up to ∼0.5%
(relative ∼1.8%). We also reveal that such filters can be used
to regulate the energy output of solar cells throughout a day or year,
and can reduce the thickness of the absorber layer by up to 40%. We
anticipate that similar gains would be seen at other latitudes. As
this filter has complex wavelength-direction functionality, we present
a proof-of-concept design based on Luneburg lenses, demonstrating
these filters can be realized. Our results will enable solar cells
with higher efficiency and more stable output while using less material.