The latest progress and future perspectives of thin film photovoltaic kesterite technology are reviewed herein. Kesterite is currently the most promising emerging fully inorganic thin film photovoltaic technology based on critical raw-material-free and sustainable solutions. The positioning of kesterites in the frame of the emerging inorganic solar cells is first addressed, and the recent history of this family of materials briefly described. A review of the fast progress achieved earlier this decade is presented, toward the relative slowdown in the recent years partly explained by the large opencircuit voltage (V OC ) deficit recurrently observed even in the best solar cell devices in the literature. Then, through a comparison with the close cousin Cu(In,Ga)Se 2 technology, doping and alloying strategies are proposed as critical for enhancing the conversion efficiency of kesterite. In the second section herein, intrinsic and extrinsic doping, as well as alloying strategies are reviewed, presenting the most relevant and recent results, and proposing possible pathways for future implementation. In the last section, a review on technological applications of kesterite is presented, going beyond conventional photovoltaic devices, and demonstrating their suitability as potential candidates in advanced tandem concepts, photocatalysis, thermoelectric, gas sensing, etc.Kesterite Photovoltaics He has supervised ten Ph.D. theses in the photovoltaic field. He is currently the coordinator of the research and innovation H2020 project STARCELL (www.starcell.eu), and the RISE (Marie Curie) project INFINITE-CELL (www.infinite-cell.eu).the V OC deficit for bandgaps close to 1.0 or 1.5 eV are comparable, and one can consider that kesterite is reasonably close to the state of the art of chalcopyrite materials in that range. But, while for kesterite the V OC deficit increases almost monotonically with the bandgap, it is markedly reduced for intermediate

A fundamental analysis of the impact of Ge on the synthesis of Cu2ZnSnSe4:Ge by a sequential process is presented, reporting the consequences on the absorber morphology and solar cell devices performance.

Improvement of the efficiency of Cu(2)ZnSnS(4) (CZTS)-based solar cells requires the development of specific procedures to remove or avoid the formation of detrimental secondary phases. The presence of these phases is favored by the Zn-rich and Cu-poor conditions that are required to obtain device-grade layers. We have developed a selective chemical etching process based on the use of hydrochloric acid solutions to remove Zn-rich secondary phases from the CZTS film surface, which are partly responsible for the deterioration of the series resistance of the cells and, as a consequence, the conversion efficiency. Using this approach, we have obtained CZTS-based devices with 5.2% efficiency, which is nearly twice that of the devices we have prepared without this etching process.