Dye-Sensitized Solar Cells Based on Nanostructured Semiconductor Oxide Ceramics with Ultra-Thin Barrier Layers

Abstract

Nanostructured high band-gap oxide semiconductor ceramics are extensively investigated to understand their unique properties and applications in dye-sensitized solar cells, sensors, supercapacitors and other electronic and electrochemical devices. The unusual properties of these materials originate from large surface-area to bulk-volume ratio, quantum size effects and formation of space charge layers of dimensions comparable to the crystallite size in depletion of carriers. A prototype device demonstrating the unique properties of nanostructured semiconductor ceramics is the dye-sensitized solar cell. The original version of this device is based on TiO 2 and other familiar stable oxides SnO 2 and ZnO yield lower efficiencies owing to faster recombination. SnO 2 admits faster electron transport because of the lower effective electron mass, but the same property enhances recombination. Ultra-thin barrier layers insulating stannates coated over the SnO 2 crystallites by glazing with alkaline earth chlorides increases the efficiency from ∼1 to 6.6%.

Enhanced Performance of Flexible Dye-Sensitized Solar Cells: Electrodeposition of Mg(OH)2 on a Nanocrystalline TiO2 Electrode

“…Although thicker coatings may screen electron leakage effectively, the charge tunnelling probability falls exponentially against the barrier width. 27 Hence, thick Mg(OH) 2 coatings on the electrode surface reduce the photocurrent significantly. 28 The isoelectric point of Mg(OH) 2 is pH 12 22 compared to pH 6.50 11 for TiO 2 , therefore, the Mg(OH) 2 surface is more basic and forms strong bonding with dye.…”

“…In DSCs made with Mg(OH) 2 coating, the photogenerated electrons (injected from the dye molecules attached to the Mg(OH) 2 surface) have the capability to tunnel across the Mg(OH) 2 barrier if the coating is thin enough. Although thicker coatings may screen electron leakage effectively, the charge tunnelling probability falls exponentially against the barrier width . Hence, thick Mg(OH) 2 coatings on the electrode surface reduce the photocurrent significantly .…”