Exploring excited states of Pt(ii) diimine catecholates for photoinduced charge separation

Paul A. Scattergood, Patricia Jesus, Harry Adams, Milan Delor, Igor V. Sazanovich, Hugh D. Burrows, Carlos Serpa, Julia A. Weinstein

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

The intense absorption in the red part of the visible range, and the presence of a lowest charge-transfer excited state, render Platinum(ii) diimine catecholates potentially promising candidates for light-driven applications. Here, we test their potential as sensitisers in dye-sensitised solar cells and apply, for the first time, the sensitive method of photoacoustic calorimetry (PAC) to determine the efficiency of electron injection in the semiconductor from a photoexcited Pt(ii) complex. Pt(ii) catecholates containing 2,2′-bipyridine-4,4′-di-carboxylic acid (dcbpy) have been prepared from their parent iso-propyl ester derivatives, complexes of 2,2′-bipyridine-4,4′-di-C(O)OiPr, (COOiPr)2bpy, and their photophysical and electrochemical properties studied. Modifying diimine Pt(ii) catecholates with carboxylic acid functionality has allowed for the anchoring of these complexes to thin film TiO2, where steric bulk of the complexes (3,5-ditBu-catechol vs. catechol) has been found to significantly influence the extent of monolayer surface coverage. Dye-sensitised solar cells using Pt(dcbpy)(tBu2Cat), 1a, and Pt(dcbpy)(pCat), 2a, as sensitisers, have been assembled, and photovoltaic measurements performed. The observed low, 0.02-0.07%, device efficiency of such DSSCs is attributed at least in part to the short excited state lifetime of the sensitisers, inherent to this class of complexes. The lifetime of the charge-transfer ML/LLCT excited state in Pt((COOiPr)2bpy)(3,5-di-tBu-catechol) was determined as 250 ps by picosecond time-resolved infrared spectroscopy, TRIR. The measured increase in device efficiency for 2a over 1a is consistent with a similar increase in the quantum yield of charge separation (where the complex acts as a donor and the semiconductor as an acceptor) determined by PAC, and is also proportional to the increased surface loading achieved with 2a. It is concluded that the relative efficiency of devices sensitised with these particular Pt(ii) species is governed by the degree of surface coverage. Overall, this work demonstrates the use of Pt(diimine)(catecholate) complexes as potential photosensitizers in solar cells, and the first application of photoacoustic calorimetry to Pt(ii) complexes in general.

LanguageEnglish
Pages11705-11716
Number of pages12
JournalDalton Transactions
Volume44
Issue number26
Early online date23 Jan 2015
DOIs
Publication statusPublished - 14 Jul 2015
Externally publishedYes

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Excited states
Photoacoustic effect
Calorimetry
2,2'-Dipyridyl
Carboxylic Acids
Charge transfer
Semiconductor materials
Electron injection
Photosensitizing Agents
Quantum yield
Platinum
Electrochemical properties
Infrared spectroscopy
Monolayers
Solar cells
Esters
Derivatives
Thin films
catechol
Dye-sensitized solar cells

Cite this

Scattergood, P. A., Jesus, P., Adams, H., Delor, M., Sazanovich, I. V., Burrows, H. D., ... Weinstein, J. A. (2015). Exploring excited states of Pt(ii) diimine catecholates for photoinduced charge separation. Dalton Transactions, 44(26), 11705-11716. https://doi.org/10.1039/c4dt03466j
Scattergood, Paul A. ; Jesus, Patricia ; Adams, Harry ; Delor, Milan ; Sazanovich, Igor V. ; Burrows, Hugh D. ; Serpa, Carlos ; Weinstein, Julia A. / Exploring excited states of Pt(ii) diimine catecholates for photoinduced charge separation. In: Dalton Transactions. 2015 ; Vol. 44, No. 26. pp. 11705-11716.
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abstract = "The intense absorption in the red part of the visible range, and the presence of a lowest charge-transfer excited state, render Platinum(ii) diimine catecholates potentially promising candidates for light-driven applications. Here, we test their potential as sensitisers in dye-sensitised solar cells and apply, for the first time, the sensitive method of photoacoustic calorimetry (PAC) to determine the efficiency of electron injection in the semiconductor from a photoexcited Pt(ii) complex. Pt(ii) catecholates containing 2,2′-bipyridine-4,4′-di-carboxylic acid (dcbpy) have been prepared from their parent iso-propyl ester derivatives, complexes of 2,2′-bipyridine-4,4′-di-C(O)OiPr, (COOiPr)2bpy, and their photophysical and electrochemical properties studied. Modifying diimine Pt(ii) catecholates with carboxylic acid functionality has allowed for the anchoring of these complexes to thin film TiO2, where steric bulk of the complexes (3,5-ditBu-catechol vs. catechol) has been found to significantly influence the extent of monolayer surface coverage. Dye-sensitised solar cells using Pt(dcbpy)(tBu2Cat), 1a, and Pt(dcbpy)(pCat), 2a, as sensitisers, have been assembled, and photovoltaic measurements performed. The observed low, 0.02-0.07{\%}, device efficiency of such DSSCs is attributed at least in part to the short excited state lifetime of the sensitisers, inherent to this class of complexes. The lifetime of the charge-transfer ML/LLCT excited state in Pt((COOiPr)2bpy)(3,5-di-tBu-catechol) was determined as 250 ps by picosecond time-resolved infrared spectroscopy, TRIR. The measured increase in device efficiency for 2a over 1a is consistent with a similar increase in the quantum yield of charge separation (where the complex acts as a donor and the semiconductor as an acceptor) determined by PAC, and is also proportional to the increased surface loading achieved with 2a. It is concluded that the relative efficiency of devices sensitised with these particular Pt(ii) species is governed by the degree of surface coverage. Overall, this work demonstrates the use of Pt(diimine)(catecholate) complexes as potential photosensitizers in solar cells, and the first application of photoacoustic calorimetry to Pt(ii) complexes in general.",
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Scattergood, PA, Jesus, P, Adams, H, Delor, M, Sazanovich, IV, Burrows, HD, Serpa, C & Weinstein, JA 2015, 'Exploring excited states of Pt(ii) diimine catecholates for photoinduced charge separation', Dalton Transactions, vol. 44, no. 26, pp. 11705-11716. https://doi.org/10.1039/c4dt03466j

Exploring excited states of Pt(ii) diimine catecholates for photoinduced charge separation. / Scattergood, Paul A.; Jesus, Patricia; Adams, Harry; Delor, Milan; Sazanovich, Igor V.; Burrows, Hugh D.; Serpa, Carlos; Weinstein, Julia A.

In: Dalton Transactions, Vol. 44, No. 26, 14.07.2015, p. 11705-11716.

Research output: Contribution to journalArticle

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T1 - Exploring excited states of Pt(ii) diimine catecholates for photoinduced charge separation

AU - Scattergood, Paul A.

AU - Jesus, Patricia

AU - Adams, Harry

AU - Delor, Milan

AU - Sazanovich, Igor V.

AU - Burrows, Hugh D.

AU - Serpa, Carlos

AU - Weinstein, Julia A.

PY - 2015/7/14

Y1 - 2015/7/14

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AB - The intense absorption in the red part of the visible range, and the presence of a lowest charge-transfer excited state, render Platinum(ii) diimine catecholates potentially promising candidates for light-driven applications. Here, we test their potential as sensitisers in dye-sensitised solar cells and apply, for the first time, the sensitive method of photoacoustic calorimetry (PAC) to determine the efficiency of electron injection in the semiconductor from a photoexcited Pt(ii) complex. Pt(ii) catecholates containing 2,2′-bipyridine-4,4′-di-carboxylic acid (dcbpy) have been prepared from their parent iso-propyl ester derivatives, complexes of 2,2′-bipyridine-4,4′-di-C(O)OiPr, (COOiPr)2bpy, and their photophysical and electrochemical properties studied. Modifying diimine Pt(ii) catecholates with carboxylic acid functionality has allowed for the anchoring of these complexes to thin film TiO2, where steric bulk of the complexes (3,5-ditBu-catechol vs. catechol) has been found to significantly influence the extent of monolayer surface coverage. Dye-sensitised solar cells using Pt(dcbpy)(tBu2Cat), 1a, and Pt(dcbpy)(pCat), 2a, as sensitisers, have been assembled, and photovoltaic measurements performed. The observed low, 0.02-0.07%, device efficiency of such DSSCs is attributed at least in part to the short excited state lifetime of the sensitisers, inherent to this class of complexes. The lifetime of the charge-transfer ML/LLCT excited state in Pt((COOiPr)2bpy)(3,5-di-tBu-catechol) was determined as 250 ps by picosecond time-resolved infrared spectroscopy, TRIR. The measured increase in device efficiency for 2a over 1a is consistent with a similar increase in the quantum yield of charge separation (where the complex acts as a donor and the semiconductor as an acceptor) determined by PAC, and is also proportional to the increased surface loading achieved with 2a. It is concluded that the relative efficiency of devices sensitised with these particular Pt(ii) species is governed by the degree of surface coverage. Overall, this work demonstrates the use of Pt(diimine)(catecholate) complexes as potential photosensitizers in solar cells, and the first application of photoacoustic calorimetry to Pt(ii) complexes in general.

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