Low-cost solution-processed flexible kesterite thin-film solar cells

Kesterites, Cu<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>ZnSn(S,Se)<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf>, are known for their photovoltaic (PV) application as an emerging thin-film chalcogenide solar device technology, and show high cost-effectiveness thanks to low production costs, earth-abundance and non-toxicity of their composing elements. Their solution-based synthesis makes them suitable also for flexible and Product-Integrated PV. Besides, their properties (such as energy gap, transparency, resistance, charge carrier density, and mobility) can be tuned by partial or complete substitution of one or more components allowing their employment also in tandem solar architectures. Here we report on a facile and straightforward process for the production of low-cost flexible kesterite solar cells based on wet methodologies, starting from a precursor ink deposited through blade coating. Thanks to back-contact engineering the flexible devices reached and then overcame the performances of their rigid original counterpart.