Wide bandgap tunnel layer at Sb₂Se₃/CdS heterojunction solar cells for lowering interface recombination

Significantly high voltage deficit and high diode ideality factor in Sb₂Se₃ solar cells due to space-charge region recombination, conduction band offset, and interface defects at the Sb₂Se₃/CdS heterojunction prompting elevated interfacial recombination. We proposed and theoretically analyzed an ultrathin tunnel layer to address the interfacial issues. An investigation is conducted into the function of the tunnel layer (ultrathin, wide band gap insulating layer) in mitigating the interface trap states and reducing interface recombination. The tunnel layer at the Sb₂Se₃/CdS junction has demonstrated a lower recombination current. The performance of devices demonstrated a sustained level of stability with an increase in defects when equipped with a tunnel layer, contrasting the continuous performance degradation observed in devices without a tunnel layer. The device incorporating a tunnel layer achieved an efficiency (η) of 13.9%, V_OC of 0.74 V, J_SC of 32.7 mA/cm², and FF values, of 57.2%, respectively. Conversely, the device lacking a tunnel layer at the interface exhibited efficiency parameters of 9.2%, with V_OC at 0.4 V, J_SC at 32.7 mA/cm², and a fill factor of 70.5%. The results pertaining to the optimized device with interface passivation through a tunnel layer are anticipated to serve as a catalyst for experimentation within the field.