Improved transport with 1,2-ethanedithiol treatment in the preparation of quantum-dot-nanowire solar cells

We describe the design, fabrication, and characterization of heterojunction solar cells consisting of CdSe quantum dot films sandwiched between a hole conducting polymer layer and n-type ZnO nanowires. We also present a detailed analysis of the quantum dot layer deposition processes, solution-phase ligand exchange of this quantum dot layer, the conformality of this layer on deeply nanostructured samples, and the effect of a surfactant-aided thermal anneal process. Annealing creates a structural conversion of the quantum dot layers into an extremely thin continuous polycrystalline film with typical grain diameters of 30-50 nm. This transition is accompanied by a loss of quantum confinement and a significant improvement of the charge transport in the layer. The optimized annealing and deposition processes result in solar cells with an open-circuit voltage up to 0.4 V, a short circuit current of ~10 mA/cm², an external quantum efficiency of 65%, and an energy conversion efficiency above 2%.