Improved CdS quantum dot distribution on a TiO2 photoanode by an atomic-layer-deposited ZnS passivation layer for quantum dot-sensitized solar cells

An ultrathin (< similar to 0.5 nm) ZnS interfacial passivation layer (IPL) was produced by atomic layer deposition in order to improve the performance of CdS quantum-dot (QD) sensitized solar cells. The mutable role of the top ZnS IPL, deposited after QD sensitization, enhanced light absorbance by acting as an anti-reflective coating resulting in increased photocurrent. The bottom ZnS IPL deposited on the TiO2 photoanode before QD sensitization led to a uniform distribution of smaller-sized QD microaggregates by modification of the surface energy of TiO2, which improved the photo-generated charge carrier injection from QD to TiO2. Furthermore, both ZnS IPLs have roles as the recombination barrier layer. Consequently, the photoconversion efficiency was enhanced by approximately 15% and 30% in cells with top and bottom ZnS IPLs, respectively.