ZnO/TiO₂/Sb₂S₃ Core–Shell Nanowire Heterostructure for Extremely Thin Absorber Solar Cells

Abstract

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.