The effect of post-annealing on the performance of the Cu₂ZnSnS₄ solar cells

Cu₂ZnSnS₄ (CZTS) solar cells commonly undergo post-annealing treatments to enhance their performance. However, multiple concurrent effects, including Cu–Zn disorder, Na diffusion from the back contact, CZTS grain boundary passivation, and elemental interdiffusion at the CdS/CZTS interface, can occur simultaneously during post-annealing, making it challenging to isolate their specific influence on device performance. To address this complexity, we have utilized Cu–Zn-disordered CZTS absorbers to eliminate the influence of Cu–Zn disorder in this study. Post-annealing experiments conducted at 120 to 300 °C in nitrogen and air atmospheres aim to decouple and assess the impact of different annealing conditions on the performance of CZTS solar cells. Our findings suggest that the optimal post-annealing might be a combined effect of two distinct processes: CZTS absorber surface passivation occurring at 325 °C and CdS crystallization at 225 °C. Hence, improvement in device performance could result from multiple concurrent mechanisms occurring at different temperatures.