Enhanced performance in perovskite solar cells via bromide ion substitution and ethanol treatment

•Mixed solution of PbI2 and PbBr2 with different molar ratio were used as lead precursors to obtain Pb(I1-xBrx)2 layer.•Ethanol treatment was performed to modify the morphologies of Pb(I1-xBrx)2 films.•The champion device based on MAPbI2.6Br0.4 film was achieved with a PCE of 15.53% and long term stability.