An intense research activity has been carried out in the past few years to improve efficiencies and understand limitations in kesterite based solar cells. Despite notable efforts to determine and list the different failure modes affecting the photovoltaic properties of these devices, very few works try to quantify and classify the effect of these failure modes. In this study, an exhaustive literature review has first been conducted to determine the different causes leading to limited efficiencies in kesterite devices with an additional focus on cadmium free and critical raw material free devices. Second, an original approach has been employed to quantify the impact of these failure modes on solar cells with the evaluation of feedbacks from 18 scientific experts working on kesterite technology. The result of this survey is analyzed, which allow to determine what should be the research priority for the community to improve efficiencies and drive kesterite technology to the market.

In this study, we detail a Cu 2 ZnSnSe 4 based solar cell fabrication process based on the selenization of metallic precursor stacks with elemental Se. 9.4% efficient devices without antireflection coating have been obtained. First, reproducibility issues of the process are carefully shown and discussed. It is demonstrated that device performances are strongly impacted by the precise control of the precursor composition. Then, starting from this robust process, a review of existing strategies to improve kesterite efficiencies is conducted. A significant increase in efficiency (þ1.4% absolute efficiency and þ50 mV V OC) is obtained with absorber surface treatment and post-annealing, while no effect of Ge incorporation in the precursor stack is observed. This contradictory result to most of the recent publications raises the question of the universality of this strategy to improve kesterite solar cell performance. Finding a universal activation step to boost kesterite efficiencies and bring it to the market remains a crucial need for the community.