p- to n-Type Conversion and Nonmetal-Metal Transition of Lithium-Inserted Cu3N Films

Cu3N is a semiconductor with a bandgap of similar to 1.4 eV, which is ideal for solar energy conversion applications. To obtain high-efficiency Cu3N-based solar cells, the fabrication of p-n homojunctions is desirable. Studies on the bipolar doping of Cu3N have been initiated very recently. In this study, we demonstrate that lithium-insertion into p-type Cu3N films using a soft chemical treatment causes a p- to n-type conversion and nonmetal-metal transition. This lithium insertion was achieved by treating p-type Cu3N films with n-butyllithium solutions at moderate temperatures of 313-343 K, such that the lithium atoms diffused into Cu3N and occupied the vacant interstitial sites of the crystalline lattice. As a result, the lithium-inserted Cu3N (LixCu3N) films became n-type semiconductors, indicating that the lithium atoms act as electron donors. Moreover, LixCu3N films with x>0.05 were found to show metallic electrical conductivity with resistivities of (2-4) x 10(-3) n cm. This metallic behavior was also observed in the optical transmittance and reflectance data. The findings of this study allowed us to prepare p-type, n-type, and metallic Cu3N-based films. These results may pave the way for the realization of nontoxic wholly Cu3N-based homojunction solar cells delivering high performance.