Outer-Sphere Redox Couples as Shuttles in Dye-Sensitized Solar Cells. Performance Enhancement Based on Photoelectrode Modification via Atomic Layer Deposition

Abstract

Atomic layer deposition (ALD) has been used to create conformal TiO 2 blocking layers on fluorine-doped tin-oxide substrates in dye-sensitized solar cells (DSSCs), effectively eliminating shunting. ALD has also been used to deposit, in controlled fashion, ultrathin coatings of alumina on nanoparticle-based TiO 2 DSSC photoanodes. These modified electrodes enable ferrocenium/ferrocene, an outer-sphere redox couple, to be used as a shuttle. The photovoltaic performance and interfacial charge-transfer dynamics were investigated in DSSCs employing this shuttle. It was found that a single ALD cycle is able to passivate surface states, resulting in a dramatic improvement in photovoltaic performance. Subsequent alumina deposition resulted in exponentially increasing electron lifetimes as a function of alumina layer thickness, indicating that the layers behave as barriers to electron tunneling. The characterization of DSSC photovoltaic performance and interfacial charge-transfer dynamics was extended to cells employing derivatives of ferrocenium and ferrocene featuring more positive redox potentials; these cells yielded larger open-circuit photovoltages.

Improving the efficiency of dye-sensitized solar cells by photoanode surface modifications

“…In many cases, the Al2O3 overlayer showed its effectiveness in improving the efficiency of DSSCs by forming a core-shell structure. Hamann et al [33] prepared ultrathin Al2O3 blocking layers on TiO2 by atomic layer deposition (ALD) to control the thickness of the blocking layer. The electron lifetime increased exponentially as the number of ALD cycles increased, but the photocurrent significantly decreased at the same time.…”

“…As mentioned in the second section, ALD has been used to prepare ultrathin blocking layers on mesoporous TiO2 [33]. ALD enables controlled layer-by-layer deposition of metal oxides onto templates; however, it also facilitates deposition on NP and nanorod assemblies to form core-shell structures.…”

Improved Stability of Polymer Solar Cells in Ambient Air via Atomic Layer Deposition of Ultrathin Dielectric Layers

“…[37] Recently, ALD dielectric oxides have been considered as promising candidates for reducing undesirable surface recombination in dye-sensitized and perovskite solar cells. [38][39][40][41][42][43][44][45] In addition, ALD-Al 2 O 3 was used as an EEL in PSCs with conventional architecture, [46] while our group introduced the use of ultrathin ALD-Al 2 O 3 and ZrO 2 layers to passivate surface defects of TiO 2 for improving the efficiency in inverted architecture PSCs. [47] In the current work, we successfully apply an ultrathin (<1 nm) layer of Al 2 O 3 and ZrO 2 by ALD on the surface of ZnO EELs to significantly increase both the efficiency and the stability under ambient air of intentionally un-encapsulated inverted PSCs.…”

Nanoscale electrode architectures for electrochemical energy conversion and storage.

“…31 Lund and co-workers performed numerical simulations to described edge effects in DSC and showed that there is lateral inhomogeneity in current distribution and tri-iodide concentration. 32 However, the physical origin of the edge effect was not explained in their study.…”