Temperature dependent conductivity of polycrystalline Cu2ZnSnS4 thin films

The temperature-dependent conductivity of Cu2ZnSnS4 (CZTS) thin films prepared by sulfurization of different sputtered ZnS/Cu/Sn stacks and also of the same stack annealed for different times was investigated from 30-300 K. Fitting of the through-thickness conductivity requires a model including Mott variable-range hopping (M-VRH), nearest-neighbor hopping (NNH), and thermionic emission over grain boundary (GB) barriers. The GB barrier height varies sensitively from 50-150 (+/- 5) meV with annealing and especially with [Cu]/([Zn] + [Sn]) ratio but is independent of [Zn]/[Sn] ratio. These results are critical for understanding the behavior of solar cells based on polycrystalline CZTS absorber layers. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4731875]