Growth of high material quality Aluminum Gallium Arsenide (AlxGa1-xAs) is known to be challenging, in particular with an Al content x above 20%. As a result, the use of AlxGa1-xAs in devices requiring high minority carrier lifetimes, such as solar cells, has been limited. Nonetheless, it has long been established that the substrate temperature is a key parameter in improving AlxGa1-xAs material quality. In order to optimize the growth temperature of 1.70-eV Al0.22Ga0.78As solar cells, five samples have been grown by Solid-Source Molecular Beam Epitaxy (SSMBE) at 580 degrees C, 600 degrees C, 620 degrees C, 640 degrees C, and 660 degrees C, respectively. A strong improvement in performance is observed with increasing the growth temperature from 580 degrees C to 620 degrees C. An open-circuit voltage above 1.21 V has in particular been demonstrated on the sample grown at 620 degrees C, translating into a bandgap-voltage offset W-oc below 0.5 V. Above 620 degrees C, performances in particular the short-circuit current density - moderately decrease. This trend is confirmed by photoluminescence, current density versus voltage characterization under illumination, and external quantum efficiency measurements. (C) 2017 Elsevier B.V. All rights reserved.