Flexible Kesterite Solar Cells Produced by Inkjet Printing

Among the emerging inorganic thin-film photovoltaic technologies, kesterite Cu2ZnSn(S,Se)4 (CZTSSe) is one of the most promising material thanks to its tunable bandgap of 1.0-1.5 eV according to the [S]/([S]+[Se]) ratio, which allows for an efficient harvest of an abundant portion of the solar spectrum. This material can be easily grown through different processes, both on rigid and flexible substrates, but solution-based methods, relying on the deposition of multiple layers to reach the desired thickness of the film, are currently considered as the best choice. The most common are spin-coating, blade-coating, spray pyrolysis, and dip-coating. Specifically, spin-coating led to the current record efficiency of η = 15.1%, even though the small-area limitations of this technology together with the waste of a non-negligible amount of precursor solution, still hinder the scalability of the process. Drop-on-demand inkjet printing is a promising solution-based technique that is appealing from an industrial point of view. In this work, for the first time the inkjet printing method has been applied to flexible substrates for CZTSSe thin-film solar cells. A novel 2-methoxyethanol (MOE) -based precursor solution has been properly optimized, together with the surface engineering of the flexible substrate, to allow for inkjet printing of the CZTSSe thin-film absorber. The obtained results show the first example of a working inkjet-printed flexible kesterite CZTSSe solar cell, overcoming the performance of its corresponding spin-coated counterpart by 20%, relying on a more homogenous and compact material. With inkjet printing technology, a significant reduction of preparation cost and better raw materials utilization has been possible, proving it as the most reliable path for a sustainable industrial scale-up of flexible CZTSSe solar cells.