In this Letter, we discuss the effect of Na on electrical
properties of CZTS single crystal with a systematic Na con-
centration control from Hall effect measurement. The investi-
gation of Na effect on electrical properties, such as carrier
concentration and mobility, is critically and directly correlated
to the higher performance of solar cell devices. The analysis
of the temperature dependence of the Hall effect measurement
provides valuable information about the electrical conduction
mechanism in the CZTS as well as parameters such as the
activation energy and acceptor and donor concentrations.