Ultrabroadband Quantum‐Dot Photovoltaics Enabled by a Hybrid Quad‐Graded CsSn x Ge 1− x I 3 /CaZrS 3 ‐Based Perovskite Absorber Design

This study employs SCAPS‐1D to propose and examine the first‐ever explored graded quad‐absorber hybrid stack‐based perovskite quantum dot photovoltaic cell architecture featuring four distinct absorbers (i) CsSn 0.97 Ge 0.03 I 3 with bandgap 1.308 eV, (ii) CsSn 0.75 Ge 0.25 I 3 with bandgap 1.38 eV, (iii) CsSn 0.3 Ge 0.7 I 3 with bandgap 1.59 eV, and (iv) CaZrS 3 bandgap of 1.9 eV. The systematic optimization investigates the significance of the proposed graded quad‐absorber configuration carbon nanotube (CNTS)/CsSn 0.97 Ge 0.03 I 3 /CsSn 0.75 Ge 0.25 I 3 /CsSn 0.3 Ge 0.7 I 3 /CaZrS 3 /WS 2 /fluorine‐doped tin oxide (FTO) revealing a peak optoelectronic conversion efficiency (OPCE) of 29.34%, J sc of 30.1 mA/cm 2 , V oc of 1.16 V and FF of 84.67% relative to a comparatively lower OPCE of 27.7% and 24.5% and J sc of 29 and 25 mA/cm 2 attained by its tri (CNTS/CsSn 0.75 Ge 0.25 I 3 /CsSn 0.3 Ge 0.7 I 3 /CaZrS 3 /WS 2 /FTO) absorber and dual (CNTS/CsSn 0.3 Ge 0.7 I 3 /CaZrS 3 /WS 2 /FTO)‐absorber counterparts respectively. The quad absorber stack is integrated with two‐dimensional quantum‐dot layers with WS 2 as electron transfer layer and CNT as hole transfer layer, facilitating efficient charge separation and transfer. The comparative assessment reveals that the proposed hybrid quad‐absorber stack‐based Perovskite Quantum Dot‐Solar Cellextends the spectral responsivity up to 1000 nm while maintaining a quantum efficiency of 90%. This performance surpasses that of the tri‐absorber and dual‐absorber Perovskite Quantum Dot‐Solar Cell configurations, which exhibit spectral cut‐offs at mere 900 and 800 nm, respectively.