Probably the most talked about emerging photovoltaic technology today is a material called ‘perovskites’. High efficiency solar cells using just very thin layers of perovskites have been achieved in a very short time. Despite some real hurdles having to do with the material’s stability and scalability, just about every day there are new reports on progress from research groups around the world. A strategy to bring this material to the market which is held by many research groups is to use it in ‘tandem’ with the dominant PV technology in the world today, namely the silicon wafer. Silicon wafer technology comprises 90 percent of the world’s solar panels for sale today and shows no sign of receding. So the thinking has been to combine a thin layer of perovskite material on top of the silicon wafer “in tandem”in order to achieve the higher efficiency that is needed to truly compete with fossil fuels. Importantly, higher efficiency solar panels mean fewer panels on the roof and this translates to a dramatic overall cost reduction since fewer components surrounding the solar cell, or what is known as BoS “Balance of System” components, are needed.
It is therefore remarkable that up until this past July, when a start-up based on technology by one of the most well-known materials physicists, the late Dr. Praveen Chaudhari, published a paper in connection with an Energy Conference in Scotland, there has not been a single report or article or patent on “perovskites on thin-film silicon for a high efficiency tandem solar cell”. After all, if perovskites work on a silicon wafer, isn’t it common sense to try the same on a thin-film of silicon which has the same efficiency as a polycrystalline silicon wafer yet can be made at much lower costs?
Ashok Chaudhari, CEO of Solar-Tectic, the start-up based on his late father’s technology, published a paper on this very topic – the first in the world to do so. While the paper is a “proposal,” it is based on solid data regarding the thin-film silicon component of the tandem solar cell. Moreover, the paper reports on an entirely new—patent pending – technique for growing the perovskite layer on the silicon. This has to do with the fact that technique employs tin (Sn) to achieve low temperature silicon deposition on glass. This Sn can then also – simultaneously – be used as the metal needed in the perovskite layer. Many reports of tin based perovskites have been published. Tin is non-toxic, and therefore is preferable to the more commonly used metal — lead (Pb) – in the perovskite.
From a commercial standpoint, the “perovskite/crystalline silicon thin-film tandem solar cell technology” is very exciting because it can replace the silicon wafer industry entirely. Why? Because if high efficiencies – greater than 25 percent — can be achieved at lower cost using the perovskite and thin-film silicon approach, there is no longer a need for silicon wafers. Crystalline silicon thin-film is more cost effective than silicon wafer production because it takes place at much lower temperature using less material (there are other advantages too). It is a known technology, sometimes referred to as “CSiTF” for “Crystalline Silicon Thin Film” and has been studied intensely the past 20 years or so. Amazingly, Solar-Tectic is the only company in the world with an actual patent for this technology (awarded as recently as 2015 by the US Patent and Trademark Office – US 9,054,249 B2).
Solar-Tectic has other tandem solar cell designs in the making, should the hurdles of the perovskite material prove insurmountable. For example, CZTS and III-V materials can be used in tandem with silicon, as can CIGS (or CGS). Solar-Tectic has recently filed patents for all these technologies and has world-wide protection potential for them.