Optical properties of Cu2ZnSnS4 thin films prepared by sol-gel and sulfurization method

Cu2ZnSnS4 (CZTS) thin films were prepared by a sot-gel sulfurization method. One sample (CZTS1) was stoichiometric (Cu Zn : Sn : S = 2.0 : 1.0 : 1.0 : 4.0) and another sample (CZTS2) was Cu poor and Zn rich (Cu : Zn : Sn : S = 1.87 : 1.15 1.00 : 4.00). Photoluminescence from the CZTS thin films was studied as a function of excitation power and temperature. The CZTS1 and CZTS2 thin films showed a broad luminescence between 1.1 and 1.4 eV and between 1.1 and 1.45 eV respectively. The peak photon energy of the photoluminescence was shifted to higher energy side when the excitation power was increased. The origin of the photoluminescence was attributed to donor-acceptor pair recombination with activation energy of 39 and 59 meV for CZTS1 and CZTS2 respectively. Transmittance spectra for the thin films were studied as a function of temperature. The band gap energy shift was smaller than by 10 meV with increasing temperature from 22 to 300 K.