Boosting the efficiency of single junction kesterite solar cell using Ag mixed Cu₂ZnSnS₄ active layer

We propose a silver (Ag) mixed Cu₂ZnSnS₄ (ACZTS) based solar cell architecture to improve the efficiency of single junction Cu₂ZnSnS₄ (CZTS) solar cells. The configuration exploits enhancement of depletion region using a CdS/ACZTS/CZTS architecture. The doping concentration of different layers is adapted such that the primary absorber layer (ACZTS) may become fully depleted and CZTS acts as back surface field layer. We analyze the prospect and performance of the proposed architecture through rigorous optoelectronic simulations. We also study the role of the Schottky barrier at the back-contact interface of a conventional CZTS cell. In this regard, we propose to use an Ohmic contact to increase the open circuit voltage by replacing the molybdenum (Mo) with indium tin oxide (ITO). We further optimize the ACZTS thickness and calculated a maximum obtainable efficiency of 17.59% at 550 nm ACZTS with 940 mV open circuit voltage, 24.65 mA cm^-2 short circuit current and 75.94% fill factor including the effects of Shockley-Read-Hall, radiative and surface recombination mechanisms. The efficiency of the optimized cell is ∼6.6% higher than that of the existing best single junction kesterite cell. We also vary the minority carrier life time (τ _c) and surface recombination velocity of back contact (SRV_back) and report an ideal efficiency of 22.14% with τ _c = 1 μs and SRV_back = 1000 cm s^-1. Finally, we replace the toxic CdS buffer layer with eco-friendly ZnS and observe a relative improvement of 12.91% in the efficiency. The concept proposed and analyses performed in this work advance the efficiency of single junction kesterite solar cells.