Abstract The epitaxial GaAs substrate lift-off (ELO) technique is widely used to produce thin film III–V semiconductor optoelectronic devices. However, the hydrofluoric (HF) acid used in the process forbids the incorporation of active AlGaAs device layers with high Al content due to its selective etching. In this work, a new ELO method is presented, which allows for the protection of AlGaAs layers against the HF acid attack. The method is used here to prepare and analyse thin film GaAs solar cells containing Al_0.85Ga_0.15As window layer. We employ a sacrificial GaAs buffer and device perimeter pre-processing that covers the exposed edges with back contact metals and electroplated Cu. A comparison of the epitaxially lifted GaAs solar cells with identical cells prepared by substrate etching demonstrates identical photovoltaic figures of merit and confirms the viability of the AlGaAs protection approach. In addition to applications in thin film photovoltaics, this ELO method can be applied to solid-state lasers and single-photon emitters employing AlGaAs-based Bragg reflectors, among other III–V semiconductor optoelectronic devices.