This letter reports the growth of high‐efficiency Al0.3Ga0.7As solar cells by molecular beam epitaxy. As the growth temperature increases from 650 to 750 °C, the concentration of midgap electron traps in the active layers decreases from 4×1015to less than 3×1013cm−3and the hole diffusion length in the layers improves from 2.0 to 2.6 &mgr;m. For cells grown at 750 °C, an efficiency of 14.6% (AM1.5, 100 mW/cm2for an active area) is obtained.