Performance Investigation of Organic/Inorganic Bottom Cell on Lead-Free Cs3Sb2Br9 Based All-Perovskite Tandem Solar Cell

In this work, a lead-free Cs
₃
Sb
₂
Br
₉
perovskite material is used as wide bandgap material (WBG) for top cell of the all-perovskite tandem device for the first time. A comparative study between the commonly used lead-based organic MAPbI
₃
and lead-free CsSn
_0.5
Ge
_0.5
I
₃
is performed for narrow bandgap material (NBG) for the bottom cell of the all-perovskite tandem solar cell (TSC). The current matching conditions between WBG top cell and both NBG bottom cells are observed through the variation in the thickness of perovskite materials. The effects of bottom absorbers’ thickness, absorber defect density, and carrier lifetime for both NBG perovskite solar cells (PSCs) are also investigated. Both the all-perovskite TSCs achieved excellent performance with Cs
₃
Sb
₂
Br
₉
/CsSn
_0.5
Ge
_0.5
I
₃
TSC yielding a maximum power conversion efficiency (PCE) of 20.63% with
${V}_{\text {OC}}$
of 2.19 V,
${J}_{\text {SC}}$
of 10.64 mA
$\cdot $
cm
$^{ -{2}}$
, and fill factor (FF) of 88.53%, respectively. The CsSn
_0.5
Ge
_0.5
I
₃
-based TSC demonstrated better tandem device due to all-inorganic structure with higher carrier mobility, higher effective density of state, better stability, and environment-friendly conditions under external conditions, which highlights the viability of Cs
₃
Sb
₂
Br
₉
/CsSn
_0.5
Ge
_0.5
I
₃
TSC for commercial photovoltaics (PV) technology.