Importance of interfacial passivation in the high efficiency of Sb₂Se₃ thin-film solar cells: Numerical evidence

In this paper, we demonstrate numerical evidence that interfacial passivation in the Sb₂Se₃ solar cell forming the configuration of indium tin oxide (ITO)/SnO₂/CdS/Sb₂Se₃/Au is beneficial for suppressing defects and obtaining cells with high efficiency. First, the effects of two types of defects including bulk defects in the Sb₂Se₃ absorber layer and interfacial defects at the CdS/Sb₂Se₃ interface on the performance of solar cells are studied, respectively. It is found that the effect of the bulk defects varied greatly in different magnitudes of defect density, whereas significant deterioration could be caused by the interfacial defect at relatively lower defect density. Then, the types of three actual defects named D1, D2, and D3 measured experimentally in the Sb₂Se₃ solar cells are analyzed by comparing the simulation and experimental results. It is found that the case D1 and D2 existing in the absorber layer while D3 located at the interface makes the simulation and experimental results the most consistent, in which the interfacial defect D3 contributes the most to the degradation of cell performance. Finally, a SnO₂-free Sb₂Se₃ solar cell sample is simulated to evaluate the crucial interfacial passivation effect of the SnO₂ layer. The results show that introducing a SnO₂ layer is beneficial for the passivation of not only the interfacial defects but some unclear mechanisms such as deep-level defects which are hard to be measured in the present experiment. The numerical simulation results provide evidence proving the importance of interfacial passivation in actual fabrication processes to improve the performance of Sb₂Se₃ solar cells.