The band gap of Cu₂ZnSnSe₄: Effect of order-disorder Available to Purchase

The order-disorder transition in kesterite Cu₂ZnSnSe₄ (CZTSe), an interesting material for solar cell, has been investigated by spectrophotometry, photoluminescence (PL), and Raman spectroscopy. Like Cu₂ZnSnS₄, CZTSe is prone to disorder by Cu-Zn exchanges depending on temperature. Absorption measurements have been used to monitor the changes in band gap energy (E_g) of solar cell grade thin films as a function of the annealing temperature. We show that ordering can increase E_g by 110 meV as compared to fully disordered material. Kinetics simulations show that E_g can be used as an order parameter and the critical temperature for the CZTSe order-disorder transition is 200 ± 20 °C. On the one hand, ordering was found to increase the correlation length of the crystal. But on the other hand, except the change in E_g, ordering did not influence the PL signal of the CZTSe.