The
structural and optical properties of hybrid organic–inorganic
metal halide perovskite solar cells are measured by spectroscopic
ellipsometry to reveal an optically distinct interfacial layer among
the back contact metal, charge transport, and absorber layers. Understanding
how this interfacial layer impacts performance is essential for developing
higher performing solar cells. This interfacial layer is modeled by
Bruggeman effective medium approximations (EMAs) to contain perovskite,
C60, BCP, and metal. External quantum efficiency (EQE)
simulations that consider scattering, electronic losses, and the formation
of nonparallel interfaces are created with input derived from ellipsometry
structural-optical models and compared with experimental EQE to estimate
optical losses. This nonplanar interface causes optical losses in
short circuit current density (J
SC) of
up to 1.2 mA cm–2. A study of glass/C60/SnO2/Ag or Cu and glass/C60/BCP/Ag film stacks
shows that C60 and BCP mix, but replacing BCP with SnO2 can prevent mixing between the ETLs to prevent contact between
C60 and back contact metal and enable the formation of
a planar interface between ETLs and back contact metals.
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