Epitaxial lift-off GaAs solar cell from a reusable GaAs substrate

Modifications to the existing epitaxial lift-off (ELO) method are described, which enable lift-off of large area devices (like solar cells). With the modified ELO method crack-free III–V films were obtained, up to 2 inch, in diameter and 1–6 μm thick. For the first time epitaxial lift-off GaAs solar cells were made which contained an etch sensitive Al0.85Ga0.15As window layer. An energy conversion efficiency of 9.9% (AM1.5Gxl) was measured for the ELO GaAs cells. Compared to the thick GaAs reference cell, ELO cells still suffer from a low fill factor due to series and shunt resistances. Current GaAs ELO cells represent a power to weight ratio of 200 W kg−1. Because of the high selectivity of the ELO method, GaAs substrates remain unaffected after ELO. Reuse of a GaAs substrate after ELO was investigated in order to reduce the cost of III–V solar cell modules. With a simple cleaning procedure, GaAs substrates could be used at least four times without degradation of the minority carrier lifetime or carrier mobility of the grown epilayers.