Acronym in photovoltaics: XSC for excitonic solar cell

When it comes to acronym building, the letter x is sometimes the preferred or alternate letter of a word or an affix to be carried over into the acronym—regardless of x's position in the former. For example, the acronym for extensible markup language is XML (instead of EML). The acronym XSC (but also ESC) has been used for excitonic solar cell [1].
XSCs—in contrast to conventional solar cells—function by a different mechanism involving the generation, diffusion and dissociation of excitons (see The noun exciton and the adjective excitonic).

Keywords: photovoltaic devices, solar cells, exciton

Reference
[1] Brian A. Gregg: The Photoconversion Mechanism of Excitonic Solar Cells. MRS Bulletin January 2005, 30, 20-22. PDF.