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9 January 2020

Thin Film solar will continue to grow, but beware greenwashing

Less than 5% of the world’s solar modules are made using thin film technology, but the novel idea of building integrated PV remains exciting. However, with an ever-increasing number of large corporations upping their renewables promises – it may be worth keeping an eye out for greenwashing as coating windows in solar will only go so far in slashing companies’ emissions.

The remaining 95% of the market is dominated by products using either monocrystalline or polycrystalline silicon, with only minor contributions from alternative technologies like solar thermal engines or gallium arsenide. The issue with thin film is whether or not that has the potential to change at scale.

Thin film, or amorphous silicon, uses Silane (SiH4) combined with a small amount of ‘n-type dopant’, decomposed over a thin substrate – usually stainless steel or aluminum. These conductive substrates also provide a flexible backing material for the panel alternative, removing the restriction of keeping the module in a flat format. The reduced amount of materials also slashes the weight and cost of the module.

Thin film solar actually absorbs light better than generic crystalline solar. However, efficiency in conversion to electricity is significantly reduced to between 6% and 8%, often falling to 4% after a few months of exposure to sunlight. The record within the sector has stood at 12.6% since 2013, and has proved difficult to overcome since, sitting far below the multi-junction concentrator cell efficiency of 47.1%. This is largely due to defects within crystals within the cell, blocking the flow of electrons.

Its rare that a week goes by without a new company promising a date by which it intends to be carbon neutral. Recent weeks have seen the likes of Vestas, JetBlue, Louis Vuitton and most surprisingly fossil fuel giants Repsol and Drax all upping their climate ambitions.

Without being overly cynical – after all any renewable generation is worthwhile – the allure of thin film PV will probably see several of these companies patting themselves on the back for covering swanky offices with clean energy capacity. This will probably be a key driver in the growth of the thin film sector, but it’s worth considering the low performance of this technology and the reduced solar irradiation received on the wall of a building compared to its roof.

Rather than adopting these headline-focused strategies, we would encourage these ‘climate-minded’ companies to follow the power purchasing agreement (PPA) tactics of company’s like Amazon, increasing their stakes in large scale projects where developers have optimized renewable power production through more efficient solar methods using monocrystalline silicon, tracking and bifacial technology.

Another drawback within thin film is the common use of lead within lead-halide perovskites, which make thin film cells suitable for large-area application, due to the toxicity of lead. For this reason, opportunities are limited within some markets. Recent work within Kesterite solar cells as an alternative are attempting to address this, but researchers indicate that progress is at present limited.