Highly efficient single-junction GaAs thin-film solar cell on flexible substrate

TLDR

Thin‑film solar cells are attractive for their lightweight and flexible nature, and GaAs thin‑film cells are among the most efficient, yet fabricating high‑efficiency n‑on‑p GaAs cells on flexible substrates has been hindered by technical obstacles. The authors aimed to develop a simple, rapid epitaxial lift‑off technique that leverages stress from a Cr/Au bilayer on a 125‑µm flexible substrate. They implemented the lift‑off by employing an AuBe/Pt/Au metal stack as a novel p‑type ohmic contact, enabling successful fabrication of an n‑on‑p GaAs thin‑film cell on the flexible substrate. The resulting single‑junction GaAs thin‑film cell achieved a power‑conversion efficiency of 22.08 % under AM 1.5 G illumination.

Abstract

Abstract There has been much interest in developing a thin-film solar cell because it is lightweight and flexible. The GaAs thin-film solar cell is a top contender in the thin-film solar cell market in that it has a high power conversion efficiency (PCE) compared to that of other thin-film solar cells. There are two common structures for the GaAs solar cell: n (emitter)-on-p (base) and p-on-n. The former performs better due to its high collection efficiency because the electron diffusion length of the p-type base region is much longer than the hole diffusion length of the n-type base region. However, it has been limited to fabricate highly efficient n-on-p single-junction GaAs thin film solar cell on a flexible substrate due to technical obstacles. We investigated a simple and fast epitaxial lift-off (ELO) method that uses a stress originating from a Cr/Au bilayer on a 125-μm-thick flexible substrate. A metal combination of AuBe/Pt/Au is employed as a new p-type ohmic contact with which an n-on-p single-junction GaAs thin-film solar cell on flexible substrate was successfully fabricated. The PCE of the fabricated single-junction GaAs thin-film solar cells reached 22.08% under air mass 1.5 global illumination.