Hole Concentration Reduction in CuI by Zn Substitution and its Mechanism: Toward Device Applications.

Copper iodide (CuI) is a promising p-type transparent semiconductor with excellent carrier mobility. However, the high hole concentration in conventionally fabricated CuI including the single crystal hinders its applicability to the channel layer of thin-film transistors. We found that Zn substitution into Cu + sites can effectively reduce the hole concentration. Experimental and computational examinations showed that the dominant mechanism involved the formation of a defect pair, the Zn-substituted Cu site (Zn Cu ) and Cu vacancy (V Cu ), and the simultaneous suppression of V Cu arising from the stabilization of Cu + in the Zn-substituted CuI lattice, rather than hole compensation by the electrons generated from Zn 2+ substitution into Cu + sites. Our results show that the hole concentration of Zn-substituted CuI is tunable in the range of 10 14 -10 18 cm -3 , making it suitable for thin-film transistors and hole transport layers in OLEDs.