Tandem Solar Cells Using Ternary and Quaternary Compound Semiconductors

Abstract

Tandem architectures have become of interest due to the quest to realise greater efficiency in solar
photovoltaic technologies as a way to overcome the inherent shortcomings of single-junction
devices. In ternary and quaternary compound semiconductors, such as Cu(In,Ga)Se₂ (CIGS),
Cu₂ZnSnS₄ (CZTS), Cu₂ZnSn(S,Se)₄ (CZTSSe), and Cu(In,Ga)(S,Se)₂ (CIGSeS), a range of
available band gaps, coupled with high absorption coefficients, and scalability to thin-film
technologies provides high potential in the field. The basic principles of tandem solar cell operation,
the importance of ternary and quaternary absorbers, and plan to band-gap engineer cells to make
the most of spectral sculpting and current density, is addressed in this paper.
Recent improvements are record single-junction efficiencies of more than 23% of CIGS and of the
order of 13% of CZTSSe, and simulated tandem efficiencies of almost 30% with finely tuned band-
gaps. There is still difficulty in this reversing open-circuit voltage deficits, defect states, secondary
phase formation and element scarcity of elements like indium and gallium. Alternatives such as
kesterite compounds that are sustainable are promising but performance falls short. The future
prognosis is to have a hybrid tandem of perovskite with kesterite or chalcopyrite absorbers, the
application of which provides the possibility of reaching efficiencies of over 35.
Altogether, the development of tandem solar cell with ternary and quaternary semiconductors is a
radical change in the history of photovoltaics as it stands as efficiency, sustainability and scalability
to the needs of the global renewable energy usage.