The "invention" of the DSSC.
Now and then people have asked me "Who really invented the dye sensitized cell"? Was it Prof. Grätzel, myself, Jean DeSilvestro, Helmut Tribustch, or even SK Deb? (For those surprised by the latter, SK Deb patented a TiO2/Dye photogalvanic cell in 1978.) In fact, all these people contributed, patented, or have some other claim to part of the "invention". In reality, there is no one "inventor" for the DSSC, so the question is moot. There are contributions I know about, and certainly some I don't. Finally, all I can really describe is the early work I did myself and let others decide who deserves the credit.
I started working on DSSC cells in early 1988 in the Water Chemistry Program at University of Wisconsin, Madison, under Prof. Marc Anderson. (A nice place to work, and great guy to work for.)
At that point I had been working for a year or so on high surface area TiO2 films on conductive substrates (FTO, but also metals and clay/graphite) for biotech applications. Prior to my work, Prof Anderson and a graduate student Qunyin Xu had just invented a method of making nano-porous ceramic membranes using TiO2 colloids.(1) The recipe they invented, with very small modifications, is still used today for the TiO2 in most DSSCs. The group at that time was applying the TiO2 membranes to ultrafiltration, photocatalytic purification.(2) My job was to find other applications for the TiO2. Following Honda's famous paper, we tried water splitting among other things. I spent a lot of time on the art of film formation and the firing protocols. With 10 layers of gelled colloid (spin coat) I was able to make robust 4 µm nano-porous films with very high surface area, on conductive supports with. This sounds like nothing now, but was something new at the time and quite tricky. (Tricky as I had not yet added the autoclaving step which helps film formation immensely. Those not understanding the importance of that step should try making a DSSC from Ti isopropoxide without it.) With the TiO2 films on electrodes we began investigating the electrical characteristics. At this point (early '88) the Grätzel's lab at EPFL had published 3 or 4 articles concerning visible light sensitization of TiO2 including a couple on "sol gel" films on titanium substrates.
Because the EPFL lab was also involved in photocatalysis we were aware of their work in general and noticed the articles on regenerative photocells (as we called them then). From those articles, it was clear that the films I was making in Wisconsin had much higher surface area than the EPFL ones, and could also be made on larger areas. I was making them on 10x10 cm plates at that time. I purchased some dyes, and made some initial tests from which which I got currents as high or higher than EPFL was reporting. I want to note here that I would have made much slower progress had not Prof. Grätzel been very forthcoming with up to date experimental details from EPFL. We had one or two phone conversations over 1988, and then the "serendipitous" moment occurred. I found out the Prof. Grätzel was spending the fall on sabbatical in the lab of Heinz Frei at LBL Berkeley. It so happens that Berkeley is my home town, and I had worked at LBL for 3 years prior to moving to Madison. Since I was going to spend Christmas in Berkeley as well, we agreed to meet in Heinz Frei's lab and do some experiments.
I brought my films, and Michael brought his dyes and we made very interesting cells indeed. More than that, we made what I would call the first "modern" DSSC there in that lab. Up to then, we in Wisconsin, and those at EPFL, had been using exclusively aqueous electrolytes. However in Berkeley we first tried non-aqueous iodide electrolytes. In my notes from those experiments I find that there are cells with transparent TiO2 colloidal films on FTO substrates, using ruthenium and organic dyes (phenylfluorone) and organic iodide electrolytes (ethanol). I am fairly certain that this is the first time that all these ingredients were present at the same time. The modern competitive DSSC is a vast improvement, but it contains the same basic elements. I would argue it was invented at that moment. Recall these experiments were not carried out at EPFL, nor in UW Madison. Does UC Berkeley therefore have a claim to the "invention of the DSSC" just because the experiments were done on UCB property? I don't know, and in any case all the patents from those days have expired. For those who want to debate that, I've attached scans of a few pages of my lab book from those experiments.
However, even more curious is the actual building where the experiments were carried out. It was the round lab built at UCB for Melvin Calvin after he received the Nobel prize in 1961.
Prof. Calvin and his lab.
Why is that interesting? It's a lesser known fact that Melvin Calvin was also one of the inventors of the organic photovoltaic cell, which he and David Kearns published in 1958.(3) Perhaps it was even invented in the same room? (Note: the building was not there in 1958). It is also said that Calvin spurred the start of DOE's work on photovoltaics. He is quoted as saying (in the 50s - the nuclear heyday): "If you know how to make chemical or electrical energy out of solar energy the way plants do it – without going through a heat engine – that is certainly a trick. And I'm sure we can do it. It's just a question of how long it will take to solve the technical question." Thus perhaps it's fitting that one of the ways of doing this was invented in the laboratory built for his work.
1) Anderson, M. A., Gieselmann, M. J. & Xu, Q. Titania and Alumina Ceramic Membranes. J. Membr. Sci. 39, 243 (1988).
2) a)Tunesi, S. & Anderson, M. A. Photocatalysis of 3,4-DCB in TiO2 Aqueous Suspensions; Effects of Temperature and Light Intensity; CIR-FTIT Interfacial Analysis. Chemosphere 16, 1447-1456 (1987).b) Kikkawa, H., Anderson, M. A. & O’Regan, B. The effect of Nb-Doping on the Photoelectrochemical Properties of TiO2 Membranes. Abstracts of the ACS 198, 153-COLL (1989).
3) Kearns, D. & Calvin, M. Photovoltaic Effect and Photoconductivity in Laminated Organic Systems. Journal of Chemical Physics 950 (1958).
Scans of lab book pages from 12/16/88 to 12/22/88