Emergence of flexible kesterite solar cells: progress and perspectives

Flexible photovoltaics have been and will be increasingly in demand in modern and future society in various applications. Searching for ideal flexible photovoltaic technologies that can perfectly meet these expanding demands has long been an active branch of photovoltaic research. Flexible kesterite Cu2ZnSn(S,Se)(4) (CZTSSe) has emerged in recent years owning to its great potential to be an abundant, low-cost, stable, and high-efficiency 'green' photovoltaic material that can be widely deployed with the lowest detrimental environmental impact. Here, we review the recent progress with flexible kesterite solar cells in thin-film and monograin technologies, discuss the key challenges and strategies associated with the flexible substrates, and finally provide the future perspectives on further pushing the efficiency toward commercial-competitive levels.