Boosting the efficiency of Cd-free kesterite/kesterite tandem solar cell: A numerical simulation approach

Abstract

Here we present a monolithic kesterite-based tandem solar cell to harvest sunlight from a wide spectral range. The proposed tandem structure consists of a higher band gap Cu2ZnSnS4 (CZTS) top cell and an underlying lower band gap (AgxCu1-x)2ZnSnSe4 (ACZTSe) bottom cell connected in a series circuit through a tunneling junction. In order to validate our model, CZTS based experimental solar cell has been simulated in SCAPS-1D environment considering all possible recombination pathways, which leads to a good fitting between simulated and experimental results. A careful analysis of the energy band diagram reveals that the power conversion efficiency of the experimentally designed cell was greatly affected by metal work function and interface recombination. A systematic optimization of top and bottom cells’ design by back contact modification and buffer/absorber interface engineering allows us to increase the open circuit voltage (VOC) up to 1.37 V, yielding a significant tandem efficiency of 16.2% under power matching condition. The present research is expected to provide a valuable guideline for the design and experimental fabrication of high efficiency tandem solar cells.