Predictive 1D Optoelectronic Modeling of Lead (Pb)-Free CsSn0.5Ge0.5I3/Nanocrystalline-CuInSe2 Tandem Photovoltaics

The efficiency of a single-junction photovoltaic (PV) cell is capped by thermalization loss and transmission loss. To overcome the limitations of single p-n junctions and better use of solar energy, tandem cells are the most effective method for increasing the efficiency of Photovoltaics (PVs). This work proposes monolithically integrated (2-terminal) CsSn
0.5
Ge
0.5
I
3
/Nanocrystalline-CuInSe
2
double junction tandem photovoltaic cell of two different direct bandgap semiconductors to address the toxicity concern of Pb (lead) in the perovskite structure and introduce a configuration that is low toxic, stable, and cost-effective in pursuit of long-term commercial viability. Two tandem devices with a layer sequence of—S-1: In
2
O
3
/ZnO/CsSn
0.5
Ge
0.5
I
3
/Cu
2
O/AZO/ZnSe/Nanocrystalline-CuInSe
2
/MoSe
2
/Mo; S-2: In
2
O
3
/Cu
2
O/CsSn
0.5
Ge
0.5
I
3
/ZnO/AZO/ZnSe/Nanocrystalline-CuInSe
2
/MoSe
2
/Mo have been suggested, and their performance has been analyzed numerically using the wxAMPS-modeling environment. The effect of absorber layer thickness on individual cell performance and current matching in a tandem cell is investigated. Also, transmitted spectra of the top cell and optical absorption of the tandem stack are all carefully examined by incorporating Transfer Matrix Method (TMM)–based optical simulation. An optimized power conversion efficiency of ~20% and ~15% can be achieved from S-1 and S-2 structure, respectively, by combining a high bandgap 1.5 eV CsSn
0.5
Ge
0.5
I
3
absorber at 600 nm (for S-1) and 800 nm (for S-2) with a low bandgap 1.0 eV Nanocrystalline-CuInSe
2
absorber at 900 nm (for S-1) and 850 nm (for S-2). As a result, the theoretical model presented here may facilitate the focus of efforts to discover viable solar energy materials and to improve device production and current matching of both top and bottom absorbers by controlling thickness.