Optimization of zinc to tin ratio in a sol gel precursor solution on the growth and properties of annealed czts thin films

This study focused on optimizing the Zn/Sn ratio in a precursor solution for growth and properties of annealed CZTS thin films. CZTS thin films weredeposited by sol–gel spin coating method using precursor solutions prepared by dissolving copper acetate dihydrate, zinc acetate dihydrate, tin chloride and Thiourea in methanol and Monoethylamine followed by annealing in RTP furnace at a temperature of 500oC. To optimize the Zn/Sn ratio in a precursor solution, sol–gel precursor solutions with different Zn/Sn ratios were deposited on SLG glass substrates for 30 minutes. Films with optimized Zn/Sn ratio were then annealed at different time intervals in range of 30, 60, 90 minutes. The structural, surface topology and morphology of the films were investigated using XRD, AFM and SEM. The optical and electrical measurements were obtained using UV/Vis/NIR Perkin Elma Lambda 9/19 and Ecopia HMS 3000 respectively. The XRD results showed that all films had a kesterite CZTS structure anda preferred orientation on (112) plane. All films exhibited a transmittance below 65% and had a band gap in a range of 1.30 - 1.88 eV and coefficient of absorptance of order 104 cm−1. Moreover the films with Zn/Sn ratio of 1.0 and 1.1 showed the optimaltransmittances, absorptance and optical band-gap values. The CZTS thin film exhibited p-type conductivity, resistivity ranged between 13.12- 2634 kΩ/sq and carrier concentration ranged between 1016 - 1020 cm−3. The improvements in structural, optical and electrical properties of optimal CZTS film with the increase of annealing time were observed.