High open circuit voltage quantum dot sensitized solar cells manufactured with ZnO nanowire arrays and Si/ZnO branched hierarchical structures

Quantum dot sensitized solar cells (QDSCs) are currently receiving increasing attention as an alternative to conventional dyes. The efficiencies of QDSCs have experienced a fast growth in the last years, mainly due to an increase in the reported photocurrents and fill factors. Despite this increase, further enhancement of QDSCs needs an improvement of the obtained photovoltage, V_oc, being the current main challenge in these devices. Here we show that an appropriated nanostructure of wide band gap semiconductor electrode allows us to reduce the recombination process, with a significant enhancement of V_oc. V_oc as high as 0.77 V has been demonstrated for ZnO nanowires array electrodes. The performance of the cell can be even increased to a promising 3%, using a novel photoanode architecture of "pine tree" ZnO nanorods (NRs) on Si NWs hierarchical branched structure. Most importantly, we show the necessity of exploring new electrode architectures to improve the current efficiencies of QDSCs.