Core-shell PbS/Sn:In2O3 and branched PbIn2S4/Sn:In2O3 nanowires in quantum dot sensitized solar cells
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Core-shell PbS/Sn:In2O3 and branched PbIn2S4/Sn:In2O3 nanowires have been obtained via the deposition of Pb over Sn:In2O3 nanowires and post growth processing under H2S between 100 C-200 C and 300 C-500 C respectively. The PbS/Sn:In2O3 nanowires have diameters of 50-250 nm and consist of cubic PbS and In2O3 while the PbIn2S4/Sn:In2O3 nanowires consist of PbIn2S4 branches with diameters of 10-30 nm and an orthorhombic crystal structure. We discuss the growth mechanisms and also show that the density of electrons in the n-type Sn:In2O3 core is strongly dependent on the thickness of the p-type PbS shell, which must be smaller than 30 nm to prevent core depletion, via the self-consistent solution of the Poisson-Schrï¿½dinger equations in the effective mass approximation. The PbS/Sn:In2O3 and PbIn2S4/Sn:In2O3 nanowire networks had resistances of 100-200 Ω due to the large carrier densities and exhibited defect related photoluminescence at 2.2 eV and 1.5 eV respectively. We show that PbS in contact with polysulfide electrolyte has ohmic like behavior but the PbS/Sn:In2O3 nanowires gave, rectifying current voltage characteristics as a counter electrode in a quantum dot sensitized solar cell using a conventional ITO/TiO2/CdS/CdSe photo anode, an open circuit voltage of ≈0.5 V, and short circuit current density of ≈1 mA cm-2. In contrast the branched PbIn2S4/Sn:In2O3 nanowires exhibited a higher current carrying capability of ≈7 mA cm-2 and higher power conversion efficiency of ≈2%. ï¿½ 2016 IOP Publishing Ltd.