Efficient Kesterite Solar Cells via Scalable Doctor‐Blading of 2‐Methoxyethanol‐Based Molecular Ink

Cu 2 ZnSn(S,Se) 4 (CZTSSe) thin‐film solar cells have garnered significant interest owing to their appealing properties, such as earth‐abundant composition, environmental friendliness, high light absorption coefficient and optimal bandgap. However, current high‐efficiency CZTSSe devices (>13%) are predominantly fabricated by spin‐coating, which is limited in scalability for mass production. To overcome this issue, we developed a scalable doctor‐blading method compatible with roll‐to‐roll processing. For the first time, a molecular precursor ink based on 2‐methoxyethanol solvent was adapted in doctor‐blading for CZTSSe thin film preparation. The preheating temperature was systematically optimized to obtain high‐quality precursor layers. It was found that the preheating temperature significantly influences the solvent evaporation kinetics, leading to the formation of cracks of varying sizes on the precursor film surface. At the optimal preheating temperature of 340 °C, moderately sized cracks were generated, which effectively facilitated the penetration of Se vapor during selenization and promoted grain growth in the absorber layer. This optimization notably enhanced the crystallinity and reduced the defect density of the CZTSSe absorbers. Furthermore, Kelvin probe force microscopy measurements revealed that the films preheated at 340 °C exhibited pronounced downward band bending at grain boundaries and the narrowest contact potential distribution, which effectively promoted charge carrier separation and suppressed nonradiative recombination. Consequently, a record power conversion efficiency of 13.26% was achieved for doctor‐bladed CZTSSe solar cells. This work demonstrates a viable and scalable strategy for producing low‐cost and highly efficient CZTSSe thin‐film photovoltaics.