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 materials has a photo-conversion 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 performances of ZnO nanowire-based ETA solar cells fabricated by low-cost, surface scalable, easily implemented chemical deposition techniques.
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