On the electronic structure and thermoelectric properties of BiTeBr and BiTeI single crystals and of BiTeI with the addition of BiI3 and CuI

► BiTeBr and BiTeI feature mixing of p states of Bi, Te, and halogen near Fermi level. ► BiTeBr has thermoelectric figure-of-merit ZT=0.17, two times that of BiTeI. ► 1% CuI or BiI3 decrease dramatically electron mobility in BiTeI. ► 1% CuI decreases thermal conductivity of BiTeI by a factor of 4, reaching 0.5 W m−1 K.