Realizing n-type BiCuSeO through halogens doping

Since the p-type BiCuSeO has been well developed in 2010, the maximum ZT value > 1.5 was achieved. Recently, the extensive research on n-type BiCuSeO is of interest to match its p-type counterpart. In this work, we found that n-type BiCuSeO can be successfully obtained in Bi_1.04Cu_1.05Se_0.99X_0.01O by using halogens (X = Cl, Br, I)doping. The first-principle calculations on the electronic band structure of BiCuSeO show that the Fermi levels were shifted into the conduction band by halogens doping at Se site. Both electrical transport properties and Hall measurements indicate that halogens are effective electron-dopants to realize n-type BiCuSeO. Interestingly, the results of temperature-dependent Seebeck coefficients elucidate a p-n-p type transport behavior, which experience less and less pronounced with increasing heating-cooling measurement cycles until n-type transports disappeared. Our results indicate that even though a large negative Seebeck coefficient (– 500 μV/K)can be realized in n-type BiCuSeO, but these n-type behaviors are reversible and unstable due to the fragile bonding in Cu-X (X = Cl, Br, I), and thus halogens losing upon several measurement cycles for heating and cooling. Even though our results indicate that the obtained n-type BiCuSeO is not stable through halogens doping, the calculated projected density of states elucidate that a high-performance n-type BiCuSeO can be expected by electron-doping at Bi sites.