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Mesoporous TiO 2 Beads Offer Improved Mass Transport for Cobalt‐Based Redox Couples Leading to High Efficiency Dye‐Sensitized Solar Cells
Author(s) -
Heiniger LeoPhilipp,
Giordano Fabrizio,
Moehl Thomas,
Grätzel Michael
Publication year - 2014
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201400168
Subject(s) - materials science , mesoporous material , dye sensitized solar cell , photocurrent , chemical engineering , electrolyte , cobalt , tin oxide , redox , diffusion , nanotechnology , electrode , doping , optoelectronics , biochemistry , chemistry , thermodynamics , physics , engineering , metallurgy , catalysis
Overcoming ionic diffusion limitations is essential for the development of high‐efficiency dye‐sensitized solar cells based on cobalt redox mediators. Here, improved mass transport is reported for photoanodes composed of mesoporous TiO 2 beads of varying pore sizes and porosities in combination with the high extinction YD2‐ o ‐C8 porphyrin dye. Compared to a photoanode made of 20 nm‐sized TiO 2 particles, electrolyte diffusion through these films is greatly improved due to the large interstitial pores between the TiO 2 beads, resulting in up to 70% increase in diffusion‐limited current. Simultaneously, transient photocurrent measurements reveal no mass transport limitations for films of up to 10 μm thickness. In contrast, standard photoanodes made of 20 nm‐sized TiO 2 particles show non‐linear behavior in photocurrent under 1 sun illumination for a film thickness as low as 7 μm. By including a transparent thin mesoporous TiO 2 underlayer in order to reduce optical losses at the fluorine‐doped tin oxide (FTO)‐TiO 2 interface, an efficiency of 11.4% under AM1.5G 1 sun illumination is achieved. The combination of high surface area, strong scattering behavior, and high porosity makes these mesoporous TiO 2 beads particularly suitable for dye‐sensitized solar cells using bulky redox couples and/or viscous electrolytes.