Blocking the Charge Recombination with Diiodide Radicals by TiO₂ Compact Layer in Dye-Sensitized Solar Cells

Abstract

The addition of a compact titanium dioxide (TiO 2 ) layer between the fluorine-doped tin oxide (FTO) coated glass substrate and the mesoporous TiO 2 layer in the dye-sensitized solar cell (DSC) based on the iodide/triiodide redox couple (I − /I 3 − ) is known to improve its current-voltage characteristics. The compact layer decreases the recombination of electrons extracted through the FTO layer with I 3 − around the maximum power point. Furthermore, the short-circuit photocurrent was improved, which previously has been attributed to the improved light transmittance and/or better contact between TiO 2 and FTO. Here, we demonstrate that the compact TiO 2 layer has another beneficial effect: it blocks the reaction between charge carriers in the FTO and photogenerated diiodide radical species (I 2 −• ). Using photomodulated voltammetry, it is demonstrated that the cathodic photocurrent found at bare FTO electrodes is blocked by the addition of a compact TiO 2 layer, while the anodic photocurrent due to reaction with I 2 −• is maintained. . This paper is part of the JES Focus Issue on 4D Materials and Systems.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 130.238.60.24 Downloaded on 2019-05-23 to IP ORCID Kazuteru Nonomura https://orcid.org/0000-0002-5329-9259 Nick Vlachopoulos https://orcid.org/0000-0001-5192-8122 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 130.238.60.24 Downloaded on 2019-05-23 to IP B3208 Journal of The Electrochemical Society, 166 (9) B3203-B3208 (2019) Eva Unger https://orcid.org/0000-0002-3343-867X Anders Hagfeldt https://orcid.org/0000-0001-6725-8856 Gerrit Boschloo https://orcid.org/0000-0002-8249-1469 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 130.238.60.24 Downloaded on 2019-05-23 to IP

Electron-Selective Layers for Dye-Sensitized Solar Cells Based on TiO2 and SnO2

“…ESL thus enhances the open-circuit voltage, V OC , and fill factor of both types of photovoltaics. Additional benefits of ESL follow from improved physical and electrical contacts between FTO and the mesoporous oxide semiconductor (usually TiO 2 ) and enhanced optical transmittance. , Specifically, in the I 3 – /I – -mediated DSSCs, this layer blocks the reaction of electrons with photo-generated I 2 – · radical anions, thus enhancing not only the V OC but also the photocurrent …”

“…Additional benefits of ESL follow from improved physical and electrical contacts between FTO and the mesoporous oxide semiconductor (usually TiO 2 ) 9 and enhanced optical transmittance. 9,10 Specifically, in the I 3 − /I −mediated DSSCs, this layer blocks the reaction of electrons with photo-generated I 2 −• radical anions, thus enhancing not only the V OC but also the photocurrent. 9 The traditional DSSCs with Ru sensitizers and the I 3 − /I − redox mediator work reasonably well even in the absence of ESL, which is ascribed to the fact that (i) the Ru dye itself can effectively screen the electron transfer from FTO to the electrolyte and (ii) the I 3 − /I − exchange current is very small on FTO.…”

“…9,10 Specifically, in the I 3 − /I −mediated DSSCs, this layer blocks the reaction of electrons with photo-generated I 2 −• radical anions, thus enhancing not only the V OC but also the photocurrent. 9 The traditional DSSCs with Ru sensitizers and the I 3 − /I − redox mediator work reasonably well even in the absence of ESL, which is ascribed to the fact that (i) the Ru dye itself can effectively screen the electron transfer from FTO to the electrolyte and (ii) the I 3 − /I − exchange current is very small on FTO. 1−4 Yet, already the pioneering works 11,12 noticed a significant performance improvement if few monolayers of dense TiO 2 were electrochemically deposited 13 over the FTO/ mesoporous TiO 2 in the originally "ESL-free" cell architecture.…”

n-type polyaniline hole-blocking layer for high-efficiency QDSC by one-pot electropolymerization and selective aprotic cation ([EMIM]+) doping

“…In photovoltaic conversion processes, the charge exportation loss of photoelectrodes severely restricts device efficiency. Accordingly, as the photoanode terminal for photoelectron exportation, the hole-blocking layer (HBL) segment assumes an essential role for improving device efficiency [10,11]. Except for the simple physical hole-blocking function, the electron driving force and transfer capacity of HBLs are still the short boards of electron transfer capability in the combined photoanode.…”