A hierarchically organized photoelectrode architecture for highly efficient CdS/CdSe-sensitized solar cells

A form of photoelectrode architecture suitable for inorganic semiconductor solar cells is reported. The developed architecture consists of hierarchically organized TiO₂ nanostructures with several tens of nanometer-sized particles that have a large surface area and open channels with several hundred-nanometer-gaps perpendicular to the substrate. These are tailored by controlling the kinetic energy of the ablated species during pulsed laser deposition (PLD). To fabricate the solar cells, CdS and CdSe inorganic sensitizers are assembled onto the architecture by successive ionic layer adsorption and reaction and polysulfide solution is used as an electrolyte with lead sulfide counter-electrodes. The inorganic semiconductor solar cells using the developed architecture (PLD-TiO₂) show high energy conversion efficiencies of 5.57% compared to a conventional mesoporous TiO₂ film(NP-TiO₂) (3.84%) with an optical mask at 1 sun of illumination. The improved cell performance of PLD-TiO₂ is attributed to greater light-harvesting ability, which results in the enhancement of the J_sc value. PLD-TiO₂ absorbs more CdS/CdSe because of its larger surface area and excellent adhesion properties with fluorine-doped tin oxide (FTO) substrates. Additionally, due to its unique channel-shaped architecture, PLD-TiO₂ has a longer electron lifetime compared to NP-TiO ₂. With their unique nanostructured architecture, hierarchically organized TiO₂ nanostructures consisting of open channels of pores are investigated as photoelectrodes for CdS/CdSe-sensitized solar cells (CSSCs). The fabricated CSSCs show an overall energy conversion efficiency of 5.57%, which is highest performance in a CdS/CdSe system. This superior photovoltaic performance comes from the excellent electron lifetime due to the formation of open channels of pores