Extremely
thin absorber (ETA) solar cells integrating ZnO nanowires
have been receiving increasing interest owing to efficient light-trapping
phenomena and charge-carrier management, but the chemical instability
of ZnO in acidic conditions limits its combination with a variety
of absorbing semiconducting shells grown by chemical deposition techniques.
By covering the ZnO nanowires grown by chemical bath deposition with
a protective, passivating, conformal, thin, anatase-TiO2 layer by atomic layer deposition, we show that a uniform Sb2S3 absorbing shell is formed by chemical spray
pyrolysis without structural degradation of the ZnO. The Sb2S3 absorbing shell consists of a very thin, conformal
layer together with homogeneously distributed small clusters from
the bottom to the top of the ZnO/TiO2 core–shell
nanowire arrays. The resulting ETA solar cells integrating these ZnO/TiO2/Sb2S3 core–shell nanowire heterostructures
with an Sb2S3 absorbing shell less than 10 nm-thick
and P3HT as the hole-transporting material have a photoconversion
efficiency of 2.3% with a promising short-circuit current density
of 7.5 mA/cm2 and a high open-circuit voltage of 656 mV
as one of the largest reported values in ZnO nanowire-based ETA solar
cells. The present findings thus reveal the great potential of Sb2S3 as an absorbing, semiconducting shell when coupled
with ZnO/TiO2 core–shell nanowire heterostructures,
opening the way for new strategies to improve the performance of ZnO
nanowire-based ETA solar cells fabricated by low-cost, surface-scalable,
easily implemented chemical deposition techniques.
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