Cu2ZnSnS4 thin film growth optimization and post rapid thermal annealing of solar cells and its influence on device performance

We investigated the synthesis of kesterite Cu₂ZnSnS₄ (CZTS) thin films using thermal evaporation from copper (Cu), zinc (Zn) and tin (Sn) pellets and post-annealing in a sulfur atmosphere. Two different metal precursor stacking orders (Cu/Sn/Zn/Cu and Cu/Sn/Cu/Zn) have been tested and experimental results prove that a layer of Cu on the top provides higher compositional uniformity and fewer secondary phases. CZTS thin films produced by a Cu/Sn/Zn/Cu precursor stacking order was used to study post rapid thermal annealing (RTA) influence on solar cell performance. The best performing solar cell using the CZTS thin film mentioned above with composition ratio Cu/(Zn+Sn) = 0.82, and Zn/Sn = 1.35 exhibited an open-circuit voltage of 433 mV, a short-circuit current of 7.78 mA/cm², a fill factor of 46.23% and a conversion efficiency of 1.56%. Post RTA was conducted and an increase of device performance was observed. The solar cell which shows 1.56% at room temperature shows 2.72% efficiency after RTA at 350°C for 30 seconds. The cell performance improvement mechanism was studied.