A Comparison Between the Behavior of Nanorod Array and Planar Cd(Se, Te) Photoelectrodes

Analysis of the full device generation, transport, and recombination equations has shown that nanorod junction arrays can potentially offer improved photovoltaic performance relative to planar junctions for a carrier-collection limited absorber material not characterized by an excessively high rate of depletion-region recombination. To test this hypothesis, we have characterized planar and nanorod array photoelectrodes prepared by electrodeposition of Cd(Se, Te). The photoelectrochemical behavior of each type of photoelectrode was measured in contact with a liquid electrolyte consisting of aqueous 1 M S_2^(2-)/S^(2-), 1 M NaOH. The open-circuit photovoltage, V_(oc), short-circuit current density, J_(sc), fill factor, and overall energy conversion efficiency for both types of electrodes was measured under simulated 100 mW cm^(-2), Air Mass 1.5 conditions. V_(oc), J_(sc), and overall efficiencies were lower, on average, for nanorod array Cd(Se,Te) photoelectrodes, while the fill factors of the nanorod array photoelectrodes were generally superior to those of the planar junction devices. Importantly, the spectral response of the nanorod array photoelectrodes exhibited better quantum yields for collection of near-IR photons relative to collection of high-energy photons than did the planar photoelectrodes, in agreement with predictions of the theoretical model. The effects of surface recombination and junction area for both electrode designs have also been evaluated relative to planar photoelectrode junctions, using the Cd(Se,Te) electrode as a model system for the properties of nanorod array photoelectrodes.