Kesterite Absorbers for Flexible Solar Cells—Milestones and Current Scenario

The rapid surge in energy demand and concerns over global warming have led to the use of nonconventional and green energy sources to replace conventional fossil fuels. Although the photovoltaic industry has experienced significant growth over the past two decades, a gap remains in optimising the utilisation of solar energy. This gap can be addressed by developing flexible photovoltaic devices (FPVDs). Among the various types of solar cells, kesterite‐based solar cells have proven to be an environmentally safe, inexpensive, and stable option. Flexible energy conversion and storage devices are widely preferred for the development of wearable electronic devices. Unlike rigid photovoltaic devices, fabricating flexible devices requires careful analysis and selection of the substrate, as well as control over absorber characteristics. Additionally, the method used to form the active layer and the stacking order of the functional layers in kesterite materials also influence device performance. The absence of a rigid substrate in flexible devices makes doping with alkali materials a crucial step to prevent detrimental defects and secondary phase formation. This review examines recent developments in kesterite‐based FPVD. It discusses various aspects, including substrate selection, defect origins, control of secondary phases, different doping strategies, and new techniques for active‐layer formation, such as adhesive‐bonding transfer, plasma‐jet utilisation, and monograin layer formation. Bending characteristics that significantly affect FPVD performance have also been discussed in detail.