Assessment of the photovoltaic properties of CZTS grown on representative Si solar cell structures for monolithic CZTS/Si tandem applications

The prospect of increasing the efficiency of pure sulfide Cu2ZnSnS4 (CZTS) opens up the possibility of using it as a high bandgap partner in tandem photovoltaics, in particular with a Si-based bottom cell. Although the growth of CZTS on monocrystalline Si has been discussed in recent years, the implications of such growth for real and representative monolithic CZTS/Si tandem structures are hardly ever discussed.
In this work, we grow CZTS by co-sputtering precursors on a representative Tunnel Oxide Passivated Contact (TOPCon) n-Si structure, and investigate how the growth conditions and bottom cell structure affect the photovoltaic properties of CZTS. In particular, CZTS is grown on two different layers: the n-type poly-Si electron selective layer, and a TiN barrier layer. The properties of the resulting CZTS films are compared to those of a baseline single junction CZTS solar cell, and it is shown that the resulting CZTS films can differ considerably. The advantages and limitations of each resulting case are then used to assess the potential of achieving high-quality CZTS absorbers without compromising the performance of the bottom Si cell. Based on this, an elementary monolithic CZTS/Si tandem device is presented, and the aspects behind its low performance are discussed based on the work conducted.