Does hole transport between dyes contribute to the photoconversion efficiency of solid state DSSCs?

Piers R. F. Barnes^a, Jenny Nelson^a, Davide Moia^a, Henry J. Snaith^b, Tomas Leijtens^b, Xiaoe Li^c, Brian C. O'Regan^c, Ute B. Cappel^c

^aDepartment of Chemistry and Centre for Plastic Electronics, Imperial College London, South Kensington Campus, London, United Kingdom

^bDepartment of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom

^cDepartment of Chemistry, Imperial College London, South Kensington Campus London, London, United Kingdom

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Oral, Davide Moia, presentation 178
Publication date: 5th February 2015

Yes! Intermolecular charge transport between molecules chemically anchored to the surface of oxide nanocrystals has been demonstrated previously for films immersed in inert electrolytes.¹^,² The phenomenon has been applied to high performance lithium ion batteries,³ electrochromic devices⁴and solar fuel production.⁵A contribution to the photoconversion efficiency of solid state dye sensitized solar cells (DSSCs) from hole transfer between dyes sensitizing the surface of TiO₂ has been proposed⁶but not demonstrated before now. Here we show a clear correlation between the level of hole percolation through D131 dye monolayers on a macroscopic scale (measured using cyclic voltammetry) and intermolecular transport on a nanoscopic scale (measured using transient absorption anisotropy). In light of this result we then measured the yield of dyes regenerated in solid state DSSCs with high and low dye loadings (i.e. with and without hole percolation between dyes) on mesoporous TiO₂ films infiltrated with varying levels of hole transport material (HTM). Thus, we have quantified the fraction of dye regeneration attributable to inter-dye hole percolation. This fraction can be >50% of the overall regenerated dyes under low pore filling conditions and is reduced to about 5% when the infiltration of the HTM in the pores is optimized. We have therefore clarified the process of charge collection in this class of devices and demonstrated that hole percolation in the dye monolayer is necessary to achieve 100% regeneration yield. Furthermore, quantification of inter-dye hole percolation can also be used as probe of other characteristics of mesoporous oxide systems. First, we present insights into the distribution and morphology of the infiltrated HTM phase in the pores. Secondly, we probe electron transport and trapping in the TiO₂ scaffold by analysing the dependence of electron-hole recombination kinetics on the ability of holes to migrate across the surface of the nanocrystals.
Figure 1. Time dependent regeneration yield of solid state DSSCs, resolved for systems where hole transport between dyes on the surface of the TiO2 is either allowed or stopped.
(1) Bonhôte, P.; Gogniat, E.; Tingry, S.; Barbe, C.; Vlachopoulos, N.; Lenzmann, F.; Comte, P.; Graetzel, M. Efficient Lateral Electron Transport inside a Monolayer of Aromatic Amines Anchored on Nanocrystalline Metal Oxide Films. J. Phys. Chem. B 1998, 5647, 1498-1507. (2) Moia, D.; Vaissier, V.; López-Duarte, I.; Torres, T.; Nazeeruddin, M. K.; O’Regan, B. C.; Nelson, J.; Barnes, P. R. F. The Reorganization Energy of Intermolecular Hole Hopping between Dyes Anchored to Surfaces. Chem. Sci. 2014, 5, 281. (3) Wang, Q.; Evans, N.; Zakeeruddin, S. M.; Exnar, I.; Grätzel, M. Molecular Wiring of Insulators: Charging and Discharging Electrode Materials for High-Energy Lithium-Ion Batteries by Molecular Charge Transport Layers. J. Am. Chem. Soc. 2007, 129, 3163-3167. (4) Wang, Q.; Zakeeruddin, S. M.; Cremer, J.; Bäuerle, P.; Humphry-Baker, R.; Grätzel, M. Cross Surface Ambipolar Charge Percolation in Molecular Triads on Mesoscopic Oxide Films. J. Am. Chem. Soc. 2005, 127, 5706-5713. (5) Ardo, S.; Meyer, G. J. Characterization of Photoinduced Self-Exchange Reactions at Molecule-Semiconductor Interfaces by Transient Polarization Spectroscopy: Lateral Intermolecular Energy and Hole Transfer across Sensitized TiO2 Thin Films. J. Am. Chem. Soc. 2011, 133, 15384-15396. (6) Weisspfennig, C. T.; Hollman, D. J.; Menelaou, C.; Stranks, S. D.; Joyce, H. J.; Johnston, M. B.; Snaith, H. J.; Herz, L. M. Dependence of Dye Regeneration and Charge Collection on the Pore-Filling Fraction in Solid-State Dye-Sensitized Solar Cells. Adv. Funct. Mater. 2013, 24, 668-677.

nanoGe is a prestigious brand of successful science conferences that are developed along the year in different areas of the world since 2009. Our worldwide conferences cover cutting-edge materials topics like perovskite solar cells, photovoltaics, optoelectronics, solar fuel conversion, surface science, catalysis and two-dimensional materials, among many others.

MATSUS

Previously nanoGe Spring Meeting (NSM) and nanoGe Fall Meeting (NFM), MATSUS is a multiple symposia conference focused on a broad set of topics of advanced materials preparation, their fundamental properties, and their applications, in fields such as renewable energy, photovoltaics, lighting, semiconductor quantum dots, 2-D materials synthesis, charge carriers dynamics, microscopy and spectroscopy semiconductors fundamentals, etc.

International Conference on Hybrid and Organic Photovoltaics

International Conference on Hybrid and Organic Photovoltaics (HOPV) is celebrated yearly in May. The main topics are the development, function and modeling of materials and devices for hybrid and organic solar cells. The field is now dominated by perovskite solar cells but also other hybrid technologies, as organic solar cells, quantum dot solar cells, and dye-sensitized solar cells and their integration into devices for photoelectrochemical solar fuel production.

Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics

The main topics of the Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP) are discussed every year in Asia-Pacific for gathering the recent advances in the fields of material preparation, modeling and fabrication of perovskite and hybrid and organic materials. Photovoltaic devices are analyzed from fundamental physics and materials properties to a broad set of applications. The conference also covers the developments of perovskite optoelectronics, including light-emitting diodes, lasers, optical devices, nanophotonics, nonlinear optical properties, colloidal nanostructures, photophysics and light-matter coupling.

International Conference on Perovskite Thin Film Photovoltaics Perovskite Photonics and Optoelectronics

The International Conference on Perovskite Thin Film Photovoltaics Perovskite Photonics and Optoelectronics (NIPHO) is the best place to hear the latest developments in perovskite solar cells as well as on recent advances in the fields of perovskite light-emitting diodes, lasers, optical devices, nanophotonics, nonlinear optical properties, colloidal nanostructures, photophysics and light-matter coupling.