Catch the sun: new ancillary ligands in Copper(I) dye-sensitized solar cells lead to panchromatic light harvesting

The world population is increasing. More people demand better living conditions and the boom in the developing countries continues apace. The story of human progress is also the story of energy. Energy was and will be the key feature of progress. Nowadays, three energy transitions have taken place. These have developed our society from wood burning to coal-powered steam engines to a dependence on electricity which involved burning fossil fuels. All energy transitions up to now have included burning materials that produce not only energy but also air pollution and so-called greenhouse gases. The CO2 concentration in Earth's atmosphere is not at an acceptable level and the effects affect everyone on Earth. However, since the oil crisis in the 1970s and nuclear disasters such as Chernobyl and Fukushima, public awareness has been raised and the demand for alternative energy sources has increased. Renewable energy sources that disappeared over a long period, such as wind power, have made their comeback and a topical example of new renewable resources is photovoltaics. Photovoltaics produce renewable, sustainable and eco-friendly energy. Most commercial solar cells are based on silicon. Since their development in 1953, new generations of solar cells have been investigated in order to make them cheaper, more environmentally friendly and more efficient. Dye-sensitized solar cells are one cutting edge technology. They had their breakthrough in 1991 with the developments of Michael Grätzel and Brain O'Regan. A dye is adsorbed onto a semiconductor surface that is adhered to a conducting glass substrate. The electrical circuit is closed with a counter electrode and an electrolyte. Several types of dyes have been investigated but only a few have shown promising results. A new and exciting area encompasses copper(I)-based dyes. They consist of copper(I) complexes which incorporate a ligand with functional groups to anchor to the semiconductor surface and an ancillary ligand which can be structurally tuned to optimize light harvesting. Most of the ancillary ligands are based on a 2,2'-bipyridine core. Investigations aimed at improving cell performance had, in 2015, "got stuck" at photoconversions of around 2%. This thesis describes the path to new types of simple ancillary ligands that surpass the performance of the most optimized 2,2'-bipyridine-based ligands. The path includes the development of general methods that improve the economical part of the fabrication of the solar cells and the regeneration of destroyed dye. The new families of ancillary ligand lead to the development of panchromatic co-sensitized copper(I) dye-sensitized solar cells. For the first time, a copper(I) dye has been combined with a commercially available and cheap organic dye and the remarkable performance has shown the exciting potential of copper(I) dye-sensitized solar cells. Catch the Sun.