Metal halide perovskites owing to their excellent band
gap tunability
have shown great promise in designing two-terminal tandem solar cells
to push the limitations of single-junction devices. However, the use
of lead in perovskite absorber layers has raised several questions
in this field due to the inherent toxic nature of this element. Moreover,
most of the wide-band-gap top absorber layers that are used are composed
of mixed halides (mixture of iodine and bromine), leading to halide
segregation inside the device and affecting its long-term performance.
In order to address these issues, the present work focuses on the
simulation of a lead-free, single-halide, all-perovskite two-terminal
tandem solar cell with its physical understanding in great detail.
A total of 4 different absorber layers and 10 different charge transport
layers have been evaluated for bringing out the best device performance.
Since the band gap of the absorber layers plays a vital role in determining
the efficiency of the overall device, this work also contains a brief
summary of the band gap tuning of the perovskite crystal via compositional
engineering. It has been observed that methylammonium germanium halide
(MAGeI3), having a thickness of 930 nm, is used as a top
absorber layer when combined with FA0.75Cs0.25SnI3, which is used as a bottom absorber layer having
a thickness of 507 nm; the best-performing tandem device has been
obtained with a current density matching of 16 mA/cm2 and
a PCE of 29.26%, thus showing a lot of potential for future investigations.