Photoluminescence study of defect clusters in Cu2ZnSnS4 polycrystals

• New radiative recombination model for Cu2ZnSnS4 is presented.
• The presence of defect clusters in Cu2ZnSnS4 is observed by photoluminescence.
• The PL band at 0.66 eV at T   = 10 K is related to (CuZn−+SnZn2+) defect cluster.
• The PL band at 1.35 eV T   = 10 K is related to (2CuZn−+SnZn2+) defect cluster.

Temperature dependent photoluminescence (PL) study of Cu2ZnSnS4 (CZTS) polycrystals was performed. The low temperature PL spectrum consists of two PL bands: PL1 at 0.66 eV and PL2 at 1.35 eV. We propose a new radiative recombination model involving theoretically predicted (CuZn−+SnZn2+) and (2CuZn−+SnZn2+) defect clusters in nearly stoichiometric CZTS. PL1 band at 0.66 eV is proposed to result from a band-to-impurity type recombination related to a deep donor level at 0.66 eV below CBM that originates from the (CuZn−+SnZn2+) defect cluster. The PL2 band at 1.35 eV is found to be the dominating radiative recombination path that results from the recombination between electrons and holes in the potential wells caused by the (2CuZn−+SnZn2+) clusters that induce a significant band gap decrease of 0.35 eV in CZTS.