A patent application for Solar-Tectic LLC’s CIGS thin-film tandem solar cell has been allowed by the US Patent and Trademark Office (USPTO). The patent is the first ever for a CIGS layer on crystalline silicon thin-film (CSiTF), and covers all inorganic materials, including germanium, for the bottom layer.
More on CIGS
CIGS (Copper Indium Gallium Selenide or Sulfide) is a thin-film photovoltaic material that’s been intriguing but has suffered from inadequate efficiencies and manufacturing processes. Typical CIGS efficiencies are 13-14 percent in the market, and the record (lab) module efficiency so far is ~18 percent. In order to compete with silicon wafer technology, used in 90 percent of today’s market, efficiencies must be as high as silicon or greater, ideally between 20% – 25%; this is true even if high speed and large scale CIGS manufacturing is possible.
Ashok Chaudhari, CEO of Solar-Tectic LLC, is the inventor of this CIGS tech and says such high efficiency is achievable in a tandem, heterojunction, configuration, since CIGS (or CGS) can be tuned to have a bandgap as high as the ideal 1.8eV (in tandem with silicon). No current matching is necessary in this design.
Solar-Tectic is now the only company in the world with a patent for a CIGS tandem cell with crystalline thin-films in both layers. The amount of crystalline silicon used in the Solar-Tectic CIGS/silicon tandem technology is much less than in a silicon wafer because the crystalline silicon is a very thin film.
The fabrication processes needed for this technology are conventional and similar to those used in today’s thin-film solar cell and display industries. A product patent application for this technology was also filed and is pending in the USPTO.
Importantly, the entire process for the CIGS tandem technology is environmentally friendly since non-toxic metals are used to deposit the crystalline silicon thin-film material for the bottom layer as well as in the top, CIGS, layer. The commonly used toxic selenium (and cadmium (CdS) window layer) is not used in the ST CIGS tandem technology here. Instead, sulfur is used.
— Solar Builder magazine