The importance of the majority carrier polarity and p-n junction in titanium dioxide films to their photoactivity and photocatalytic properties

► We found undoped anatase and rutile thin films to be p- and n-type, respectively. ► We found p-type anatase to show superior photoactivity compared to n-type rutile. ► We propose that p-n junctions are formed in anatase-rutile mixture films. ► P-n junctions in anatase dominating films account for high photocatalytic property.