"Kesterite based solar cells are emerging devices with a strong interest for the development of high efficiency and low cost sustainable photovoltaic (PV) technologies. Kesterites are quaternary compounds with a crystalline structure very similar to that of chalcopyrites (CIGS: Cu(In,Ga)(S,Se)2). In contrast to CIGS - where the potential for high mass production is compromised by the scarcity of In and, to a lower extend, also Ga - they are only constituted by abundant elements.Although rapid progress has been achieved for this innovative technology in the recent years, record devices are still significantly below their chalcopyrite counterparts. Up to now, kesterite technologies have simply adapted cell designs from their chalcopyrite relatives, namely the chemical bath deposited CdS buffer and ZnO window layer. Recent findings reveal that one main limiting factor for kesterite solar cells is interface recombination at the still not optimized absorber / buffer junction.The aim of this project is to develop a deep study on the optimization of this junction, in order to achieve a significant increase in the efficiency of the devices by the use of buffer materials better adapted to the kesterite band structure. Within this scope, an in-depth analysis of state-of-the-art kesterite solar cells with respect to efficiency limiting dominant recombination paths and the buffer/absorber junction will be employed. Traditional and innovative opto-electronic techniques such as photoluminescence, Raman-based spectroscopy, temperature dependent IV- and surface photovoltage analysis will help to reveal and quantify performance limitations due to a non-optimum junction. With the aid of numerical simulation tools successfully implemented for chalcopyrite solar cells the whole solar cell design will be reconsidered with special focus on alternative buffer layers such as In2S3 or Zn(O,S)."