Morphological inhomogeneities in sprayed Cu₂ZnSnS₄ solar cells

Cutting-edge electron microscopy techniques are powerful tools to uncover morphological features that are difficult to visualize with standard microscopy techniques. In this work and for the first time, the combinatory use of scanning transmission electron microscopy (STEM) and plasma focus ion beam (PFIB) helps to reveal a high level of porosity and a low degree of recrystallization in sprayed Cu₂ZnSnS₄ thin films after a sulfurization annealing post-treatment. Despite this poor morphology, a prototype solar cell fabricated with these kesterite films shows a modest but promising PV response. Light intensity modulated impedance spectroscopy techniques, such as IMVS and IMPS, were helpful to investigate this apparent contradiction. The results suggest that the morphological defects present in the CZTS alter the carrier dynamics mainly during photocurrent generation of the device, rather than during photopotential measurements. Considering the morphological defects found in the kesterite films, we believe that the spraying procedure could be optimized to improve the crystalline quality of Cu₂ZnSnS₄ films as a pathway to produce solar cells with a competitive conversion efficiency.