Enhanced Carrier Transport Distance in Colloidal PbS Quantum-Dot-Based Solar Cells Using ZnO Nanowires

Nanostructured solar cells are a promising area of research for the production of low cost devices that may eventually be capable of complementing or even replacing present technologies in the field of solar power generation. The use of quantum dots (QDs) in solar cells has evolved from being simple absorbers in dye-sensitized solar cells to sustaining the double functions of absorbers and carrier transporters in full solid state devices. In this work, we use both optical and electrical measurements to explore the diffusion limitations of carrier transport in cells made of a heterostructure combining lead sulfide (PbS) QDs as absorbers and hole carrier and zinc oxide nanowires as electron carrier material. The results show efficient charge collection along the PbS-QD/ZnO nanowire (NW) hybrid structure. This is because of the formation of band bending in the ZnO collector, allowing efficient charge separation and spatially well-separated carrier pathways, yielding a hole transportation of over 1 mu m. We have also found a limitation in open-circuit voltage (V-oc) associated with band bending in the ZnO collector.