The band gap broadening and absorption spectrum of wurtzite Zn1−xCoxO from first-principles calculations

► The doping becomes more difficult with the increase of doping concentration. ► The appearance of the band-tail effect and the broadening of the band gaps by Co doping in ZnO. ► The heavier the doping concentration is, the broader the band gap. ► The optical absorption edge exhibits a blue-shift due to the broadening of the band gap.