“…Nevertheless, this PCE falls short compared to its competitors, specifically Cu(In,Ga)Se 2 (24.0%) and CdTe (22.7%) . The main reason for the inferior PCE in thin-film solar cells (TFSCs) based on CZTSSe is attributed to the elevated densities of defects and defect clusters, along with suboptimal microstructures featuring large grains on the top and small grains with voids at the bottom. , These flaws serve as nonradiative recombination centers, imposing a substantial restriction on the minority carrier lifetime. − Unfortunately, the thermodynamic characteristics of CZTSSe, stemming from its quaternary compositional nature and a highly restricted narrow single-phase region, accelerate the complex formation pathway of kesterite. − This phenomenon occurs irreversibly during synthesis at high temperatures under a chalcogenide vapor atmosphere, giving rise to a bilayered microstructure and the formation of abundant defect clusters of [2Cu Zn + Sn Zn ]. , Lately, various effective strategies have emerged to tackle challenges encountered in the synthesis of single-phase CZTSSe with dense microstructures. − A pivotal emphasis is placed on facilitating a direct transformation of the precursor into the kesterite phase, thereby circumventing the formation of secondary phases as well as defects. − As an example, Gong et al successfully illustrated that incorporating a fully oxidized Sn source (i.e., Sn 4+ ) in the solution precursor can directly initiate the transformation into the CZTSSe phase without intermediate phases during the synthesis process. This approach can bypass the formation reaction of secondary phases, consequently diminishing the presence of deep-level defects.…”