Improving thin-film crystalline silicon solar cell efficiencies with photonic crystals

TLDR

Most photovoltaic cells are made from crystalline silicon, whose indirect band gap leads to weak absorption of one‑third of usable solar photons. Improved light‑trapping schemes are needed, particularly for c‑Si thin‑film solar cells. A photonic crystal‑based light‑trapping approach is analyzed and compared to previous methods. For a 2‑µm c‑Si thin‑film cell with a 6‑bilayer DBR, adding a 1D grating boosts power by 24.0 %, replacing the DBR with a six‑period triangular photonic crystal increases it by 26.3 %, a DBR plus 2D grating yields 31.3 %, and an eight‑period inverse opal photonic crystal gives 26.5 %.

Abstract

Most photovoltaic (solar) cells are made from crystalline silicon (c-Si), which has an indirect band gap. This gives rise to weak absorption of one-third of usable solar photons. Therefore, improved light trapping schemes are needed, particularly for c-Si thin film solar cells. Here, a photonic crystal-based light-trapping approach is analyzed and compared to previous approaches. For a solar cell made of a 2 mum thin film of c-Si and a 6 bilayer distributed Bragg reflector (DBR) in the back, power generation can be enhanced by a relative amount of 24.0% by adding a 1D grating, 26.3% by replacing the DBR with a six-period triangular photonic crystal made of air holes in silicon, 31.3% by a DBR plus 2D grating, and 26.5% by replacing it with an eight-period inverse opal photonic crystal.