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Molecular materials for solar energy conversion
Polyhedron 82 (2014) 1
Contents lists available at ScienceDirect
Polyhedron journal homepage: www.elsevier.com/locate/poly
Editorial
Molecular materials for solar energy conversion
In the iconic movie of the 1960’s ‘‘The Graduate’’, Mr. McGuire told Benjamin that ‘‘There’s a great future in plastics’’. We have moved on since then and I believe that today he would say ‘‘There’s a great future in materials’’. This volume of Polyhedron is dedicated to the challenge of developing new molecular and extended materials for solar energy harvesting and energy conversion. I am delighted and honoured that so many of my international colleagues have contributed to this volume with 22 excellent papers covering a wide range of topics under the umbrella of Molecular materials for solar energy conversion. The volume contains both reviews and original research papers and I believe that it will provide a rich source for future workers in this highly topical area. Since their conception in 1991, Grätzel-type dye-sensitized solar cells (DSCs) have relied upon ruthenium(II)-based complexes as sensitizers for wide band-gap semiconductors, with organic dyes and, more recently, dyes containing Earth-abundant metals providing sequential advances in the field. These developments are reflected in the subjects of the reviews in this volume which span overviews of aspects of ruthenium(II) dyes (reviews by Baranoff and Rees, and Dragonetti, Abbotto and coworkers), advances in copper(I) photosensitizers and their excited state electron transfer properties to TiO2 (reviews by Castellano and Lazorski, and by Meyer and coworkers), and solar energy conversion using functionalized porphyrin dyes (a review by Coutsolelos and coworkers). Ke-Zhi Wang and coworkers provide a timely account of the photoelectric properties of polyoxometalate-based thin films, and the important contribution that computational approaches make to our understanding of electron transfer and to the development of new dyes is effectively addressed by De Angelis and coworkers. Ruthenium(II) dyes remain at the heart of many DSCs and are the subject of several contributions. Armaroli and his team present an investigation of homoleptic and heteroleptic ruthenium(II) complexes containing extended 1,10-phenanthroline-derived ligands, while the quest for thiocyanate-free ruthenium dyes (the topic of the review from Dragonetti and Abbotto) is further explored by Wai-Yeung Wong and coworkers. Light-harvesting and DSC performances of ruthenium(II) dyes bearing peripheral cyclopentadithiophene units are described by Torres, Nazeeruddin, Grätzel and coworkers, while the Falares group describe the effects of introducing a bipyridine-acrylonitrile ancillary ligand into the ruthenium(II) dye. Electrolyte optimization is a critical aspect of DSC development, and a paradigm shift from I to Co3+/Co2+ systems is seen by 3 /I some to be on the horizon. A general strategy for improving the efficiency of electron collection in ruthenium(II)-based DSCs using [Co(bpy)3]3+/2+ is presented by Carli, Caramori, Bignozzi and coworkers, and this study is complemented by results from http://dx.doi.org/10.1016/j.poly.2014.07.026 0277-5387/Ó 2014 Published by Elsevier Ltd.
Stergiopoulos, Falaras and Konstantakou focusing on blocking recombination in ruthenium(II)-based DSCs by incorporating co-adsorbents as additives in the Co(II)/(III)-based redox shuttles. Hamann and his group have combined thiocyanate-free heteroleptic ruthenium(II) cyclometalated dyes with the [Co(dmbpy)3]2+/3+ (dmbpy = 4,40 -dimethyl-2,20 -bipyridine) electrolyte, while Boschloo and Hagfeldt compare the performances of cobalt-mediated DSCs using carbon materials or platinum as the catalyst for the reduction of Co(III). Central to the development of copper(I)-base sensitizers is the choice of ligand to anchor the dye to the semiconductor. Glossman-Mitnik and his coworkers use a calculational approach to assess a family of copper(I) complexes containing biquinoline ligands functionalized with different anchoring domains. In our own work, we have found that phosphonic acid-based anchors are beneficial for copper(I) bis(diimine) dyes; our contribution to this special volume compares the use of phosphonate ester versus phosphonic acid-based anchors. In contrast to light harvesting, copper(I) complexes also have the potential to function in lightemitting electrochemical cells (LECs), and Armaroli and coworkers bring insight into this topic with a beautiful study of copper(I) complexes containing chelating P^N ligands. While LECs may also feature iridium(III) emitters, Bernhard and his team report on the potential for iridium(III) complexes containing 4,40 -dicyano-2,20 bipyridine as photosensitizers for solar fuel generation. On a related theme, Crabtree and colleagues nickel complexes as precursors for hydrogen production electrocatalysis. Two contributions focus on solid-state aspects of DSCs. Hong Lin and coworkers describe the optical and electrical properties of Cu2ZnSnS4 nanocrystals, while Leung and Yang address the important topic of optimizing scattering layers in n-type DSCs using electrospun TiO2. I take this opportunity to thank all of the contributors to this volume for the pleasurable experience of working with them and also for their individual commitments to research in a field that we all find interesting, intellectually stimulating, challenging and, probably most importantly, critical to the future of mankind. Thank you all from the bottom of my heart. Ed Constable Basel 2014 Available online 24 July 2014
Contents lists available at ScienceDirect
Polyhedron journal homepage: www.elsevier.com/locate/poly
Editorial
Molecular materials for solar energy conversion
In the iconic movie of the 1960’s ‘‘The Graduate’’, Mr. McGuire told Benjamin that ‘‘There’s a great future in plastics’’. We have moved on since then and I believe that today he would say ‘‘There’s a great future in materials’’. This volume of Polyhedron is dedicated to the challenge of developing new molecular and extended materials for solar energy harvesting and energy conversion. I am delighted and honoured that so many of my international colleagues have contributed to this volume with 22 excellent papers covering a wide range of topics under the umbrella of Molecular materials for solar energy conversion. The volume contains both reviews and original research papers and I believe that it will provide a rich source for future workers in this highly topical area. Since their conception in 1991, Grätzel-type dye-sensitized solar cells (DSCs) have relied upon ruthenium(II)-based complexes as sensitizers for wide band-gap semiconductors, with organic dyes and, more recently, dyes containing Earth-abundant metals providing sequential advances in the field. These developments are reflected in the subjects of the reviews in this volume which span overviews of aspects of ruthenium(II) dyes (reviews by Baranoff and Rees, and Dragonetti, Abbotto and coworkers), advances in copper(I) photosensitizers and their excited state electron transfer properties to TiO2 (reviews by Castellano and Lazorski, and by Meyer and coworkers), and solar energy conversion using functionalized porphyrin dyes (a review by Coutsolelos and coworkers). Ke-Zhi Wang and coworkers provide a timely account of the photoelectric properties of polyoxometalate-based thin films, and the important contribution that computational approaches make to our understanding of electron transfer and to the development of new dyes is effectively addressed by De Angelis and coworkers. Ruthenium(II) dyes remain at the heart of many DSCs and are the subject of several contributions. Armaroli and his team present an investigation of homoleptic and heteroleptic ruthenium(II) complexes containing extended 1,10-phenanthroline-derived ligands, while the quest for thiocyanate-free ruthenium dyes (the topic of the review from Dragonetti and Abbotto) is further explored by Wai-Yeung Wong and coworkers. Light-harvesting and DSC performances of ruthenium(II) dyes bearing peripheral cyclopentadithiophene units are described by Torres, Nazeeruddin, Grätzel and coworkers, while the Falares group describe the effects of introducing a bipyridine-acrylonitrile ancillary ligand into the ruthenium(II) dye. Electrolyte optimization is a critical aspect of DSC development, and a paradigm shift from I to Co3+/Co2+ systems is seen by 3 /I some to be on the horizon. A general strategy for improving the efficiency of electron collection in ruthenium(II)-based DSCs using [Co(bpy)3]3+/2+ is presented by Carli, Caramori, Bignozzi and coworkers, and this study is complemented by results from http://dx.doi.org/10.1016/j.poly.2014.07.026 0277-5387/Ó 2014 Published by Elsevier Ltd.
Stergiopoulos, Falaras and Konstantakou focusing on blocking recombination in ruthenium(II)-based DSCs by incorporating co-adsorbents as additives in the Co(II)/(III)-based redox shuttles. Hamann and his group have combined thiocyanate-free heteroleptic ruthenium(II) cyclometalated dyes with the [Co(dmbpy)3]2+/3+ (dmbpy = 4,40 -dimethyl-2,20 -bipyridine) electrolyte, while Boschloo and Hagfeldt compare the performances of cobalt-mediated DSCs using carbon materials or platinum as the catalyst for the reduction of Co(III). Central to the development of copper(I)-base sensitizers is the choice of ligand to anchor the dye to the semiconductor. Glossman-Mitnik and his coworkers use a calculational approach to assess a family of copper(I) complexes containing biquinoline ligands functionalized with different anchoring domains. In our own work, we have found that phosphonic acid-based anchors are beneficial for copper(I) bis(diimine) dyes; our contribution to this special volume compares the use of phosphonate ester versus phosphonic acid-based anchors. In contrast to light harvesting, copper(I) complexes also have the potential to function in lightemitting electrochemical cells (LECs), and Armaroli and coworkers bring insight into this topic with a beautiful study of copper(I) complexes containing chelating P^N ligands. While LECs may also feature iridium(III) emitters, Bernhard and his team report on the potential for iridium(III) complexes containing 4,40 -dicyano-2,20 bipyridine as photosensitizers for solar fuel generation. On a related theme, Crabtree and colleagues nickel complexes as precursors for hydrogen production electrocatalysis. Two contributions focus on solid-state aspects of DSCs. Hong Lin and coworkers describe the optical and electrical properties of Cu2ZnSnS4 nanocrystals, while Leung and Yang address the important topic of optimizing scattering layers in n-type DSCs using electrospun TiO2. I take this opportunity to thank all of the contributors to this volume for the pleasurable experience of working with them and also for their individual commitments to research in a field that we all find interesting, intellectually stimulating, challenging and, probably most importantly, critical to the future of mankind. Thank you all from the bottom of my heart. Ed Constable Basel 2014 Available online 24 July 2014