Progress and prospects of CZTSSe/CdS interface engineering to combat high open-circuit voltage deficit of kesterite photovoltaics: a critical review

Abstract

CZTSSe solar cells are considered to be potential and cost-effective alternative solutions to mature photovoltaic technology for meeting future energy demands. However, the current performance of CZTSSe solar cells is limited due to their high voltage deficit. The comparison of figure-of-merits of the two technologies show that CZTSSe has 62% lower open circuit voltage compared to that of 35% for CIGS, with respect to their associated band gaps. Efficient charge separation and extraction at the absorber–buffer (p–n) junction is paramount for mitigating the voltage loss and achieve high photo-conversion efficiency. The rapid progress for achieving high deliverables in CZTSSe is impeded by interface recombination, which is a consequence of poor-quality p–n junction. The inherent association of CZTSSe with secondary phases and defects due to narrow phase stability plays an unfavorable role in producing a good quality interface. The high density of interface defects, unfavorable band alignment, and structural inhomogeneities across the interface are some of the leading causes that nurture interface dominant recombination pathways. These interface-related concerns have drawn the scientific community towards interface engineering and modification of the interface to bring closer performance parity between CZTSSe and matured CIGS solar cell technology. Several approaches have attempted to develop favorable interface features that facilitate improved device performance. This work addresses the critical aspects of interface engineering of the absorber–buffer heterojunction in CZTSSe solar cells and the importance of tools that are essential to identify and eradicate the root causes of low efficiency.