Analysis of Failure Modes in Kesterite Solar Cells.

[NNadir]

The paper with the title above in the primary scientific literature comes from a new journal, ACS Applied Energy Materials and it appears in the "Editor's Choice" section on the ACS Publications page, which means that it is open sourced. I came across it while I was on my way to something else.

The full paper may be accessed here. Analysis of Failure Modes in Kesterite Solar Cells (Grenet et al ACS Applied Energy Materials ASAP, May 5, 2018)

I'm not big on reading solar "breakthrough" papers - after having sat through expositions of tens of thousands of them over half a century, half a century in which the solar industry has proved entirely useless at addressing serious environmental problems relating to dangerous fossil fuels. Mostly I poke into them with the limited interest of understanding exactly how toxic and unsustainable they are, popular "wisdom" notwithstanding.

The solar industry has not worked, is not working, and will not work to arrest the use of dangerous fossil fuels.

Not so long ago, a dumb guy, responding to my continual references to the "problem" of indium supply piped in to inform me that he had called up the web page of the Geological Survey to disprove my contention that the solar industry is not sustainable because the metals used in it are decidedly not, "renewable."

One never knows how to react to these sorts of people.

The toxic cheerleading consisted entirely of him spending 15 seconds googling "Indium" to get to the Geological Survey page that told him everything is fine, and anyway "'We'll' just recycle it" where, as usual, the "we'll" in question is not him but rather some third world person who's job it is to clean up our "green" stuff.

We don't give a shit about poor people, especially the people who will be later subjects for discussion in medical journals like this one:

Serial evaluations at an indium‐tin oxide production facility (Cummings et al Am. J. Ind. Med. 56:300–307, 2013):

Indium lung disease is a newly described disorderaffecting workers involved in the production, use, or reclamation of indium-tin oxide (ITO) [Omae et al., 2011]. Occurring as early as 1 year after first exposure, indium lung disease is marked by cough and dyspnea without a work-related pattern and abnormalities on pulmonary function tests and chest CT [Cummings et al., 2012]. Available evidence suggests that the disease begins with pulmonary alveolar proteinosis (PAP), progresses to include fibrosis and emphysema, and can cause premature death [Cummings et al., 2012]. Cross-sectional epidemiologic investigations have demonstrated an excess of lung abnormalities in workplaces where cases of indium lung disease occurred, indicating the presence of subclinical or undiagnosed disease [Chonan et al., 2007; Hamaguchi et al., 2008; Nakano et al., 2009]. A serum indium concentration of 3 mg/l or greater has been associated with adverse health effects [Nakano et al., 2009]. However, in
previous studies, exposure assessments have been lacking, and the role of serial medical testing in disease detection and prevention has not been evaluated.

Don't worry. Be happy. Copper Indium Gallium Selenide (CIGS) solar cells are "green," because, um, we live in the first world, and anyway, even if these people can't breathe because of indium, I can't live without my ITO (Indium tin oxide) cell phone.

I can't live without it. I can't.

Dumb guys aside who launch into tirades about my repeated claim that the neither the solar nor the wind nor any of the other industries called by the oxymoron "renewable energy" will ever be as safe or as sustainable or as clean as the nuclear industry, the paper cited above shows that even if the general public can't catch its breath from cheering for solar and cursing nuclear, scientists have been questioning whether the solar industry is, in fact, green.

I'll take the luxury of citing the opening paragraph of the title paper even though its open sourced and you can read it yourself:

1.1. Kesterite Solar Cells
Among the thin-film solar cell technologies, Cu(In,Ga)(S,Se)2 (CIGS) and CdTe have already demonstrated power conversion efficiency (PCE) values above 22% at laboratory scale and above 15% for large modules.(1) Industrialization of these technologies is already ongoing, with cumulative production over 4 GWp in 2016.(2) However, both of these technologies contain elements that have been listed by the European Commission as Critical Raw Materials (CRM) for the energy sector,(3,4) namely gallium, indium, and tellurium because of their scarcity in the Earth’s crust(5) and their use in other markets. Additionally, progressive implementation worldwide of regulations similar to Restriction on the Use of Hazardous Substances (RoHS) will limit or prevent the use of cadmium in these technologies,(6) both in the absorber layer (CdTe) and in the buffer layer (CdS).

Kesterite semiconductors Cu2ZnSn(S,Se)4 (CZTSSe) have been identified as promising candidates for thin-film photovoltaic (PV) applications due to their similarities to CIGS materials without containing CRM. To date, a record efficiency of 12.7% has been obtained for a CZTSSe solar cell with a CdS/In2S3 buffer layer(7) and 9.0% for a Cd and CRM-free (i.e., without Cd, In, or any CRM) kesterite solar cell.(8)

I hope it's obvious the bold is mine.

The "4GWp" expands to "4 gigawatts peak" which - given that the capacity utilization of solar cells even in deserts seldom rises above 10 - 15% - means that the entire installed solar industry in 2016, in terms of average continuous power output is the equivalent of building one 400 MW gas plant on the entire planet in 2016. (The power conversion efficiency is not the same as capacity utilization; the former refers to the percent recovery of the energy of incident light.)

Don't worry; be happy. A dumb guy can probably put their minds to rest about "CRM's" by googling his way to the USGS website on "Indium."

Returning to the paper, despite reference to "cadmium free" there's a lot of reference to Kesterite on a cadmium selenide layer, since kesterite on cadmium selenide works better than pure kesterite solar cells:



The caption:

Figure 1. Fraction of the Shockley–Queisser limit (% of SQ limit) achieved by the PV properties of the record CIGSSe, CZTSSe, CZTGSSe, Cd and CRM-free CZTSSe solar cells as a function of their bandgap. Tabulated values of the SQ limit for all parameters from ref (12). PV data and related bandgaps from refs (17?35). Bandgaps are extracted from EQE spectra.

Note that all the best performing cells using the Schockley-Queisser efficiency limit all contain cadmium.

The Schockley-Queisser limit refers to the theoretical limit of power conversion efficiency and was discovered by the famously racist Nobel Laureate William Schockley who, when he wasn't studying semiconductors claimed expertise in racist genetic theories even though he knew as little about genetics as Helen Caldicott, MD, knows about nuclear power, or as much as Albert_Olszewski MD, who is running for the Republican Senate nomination in Montana knows about climate change, even though (as noted in another post here):

Olszewski cited his scientific training and said he did not believe a human-climate link has been proven.

I don't know about you, but when I was a kid, I was very susceptible to Appeal to Authority arguments.

...as an old man, not so much.

Anyway it appears that there are lots of ways for kesterite cells to fail, and the authors give us a nice chart to show us the ways:



Oh, and in case you're laboring under the illusion that only kesterite solar cells have failure modes, I assure you that you are wrong. Every damn solar cell on this planet, pretty much, will be transformed into electronic waste within the next thirty years, especially in hot deserts.

But don't worry; be happy. Probably someone else will have to clean it up, not you, especially if you're "green."

Have a pleasant evening.