Perovskite thin film: Out with the old, in with the new

High conversion efficiency, earth-abundant material composition, and lower cost of manufacturing make perovskites a potential game changer for the solar industry. But what is the best path forward for commercialization of this exciting technology?

There has been a strong focus in the United States and in the media on perovskite-silicon tandem devices due to their potential to boost the efficiency of traditional silicon-based modules and leverage the existing silicon manufacturing base. However, research by the US Department of Energy’s National Renewable Energy Laboratory (NREL) shows that single junction perovskites can help the nation scale domestic solar quickly and free itself from a reliance on imported silicon-based products. When it comes to design, the climate crisis, energy security, and cost performance, perovskite thin film just makes more sense.

Sustainable

Less is more when it comes to product design, and the environmental benefit of a clean transition away from silicon is compelling. NREL says silicon makes up 76% of the embodied energy of a PV module, whereas thin film cells make up less than 1%. Columbia University found perovskite thin film manufacturing can reduce cumulative energy use below that of both silicon and perovskite-silicon tandems by 80% or more, regardless of production method. While silicon wafers are very thin, at 160-240 micrometers, perovskite solar cells are thinner than 1.5 micrometers – less than the thickness of a red blood cell. With thin film PV modules requiring significantly less material to manufacture, less waste passes to the end user. With perovskite-silicon tandem devices, that waste is perpetuated.

Efforts are being made to keep more PV modules out of landfills, but recycling is costly and energy intensive. To become economically viable, the recycling industry is developing more efficient methods to recover high value materials such as precious metals and silicon. The alternative is to eliminate those materials entirely and design for recyclability of a more sustainably manufactured product. Life cycle analysis by German research body Helmholtz-Zentrum Berlin found a transition from carbon-intensive silicon to perovskites added more value than any effort to improve the PV module recycling rate. If we can eliminate the highest carbon emitting component of a PV module and replace it with a more sustainable, lower cost technology, why not choose that over the hybrid? This is a no-brainer for utility power, where lowest cost of energy is the most important metric. Higher-efficiency solar solutions are often relegated to space constrained niche markets due to their cost.

Fragile silicon

China has become the global leader of PV module manufacturing but there are, quite literally, cracks in that dominance: silicon cells are inherently fragile and susceptible to microcracks. Despite efforts to minimize that risk, a recent report by Clean Energy Associates noted an exponential growth in cell crack cases in 2023, increasing 47% from the year prior. NREL research of 170 crystalline silicon systems in its PV Fleet Database found a trend of power loss after high wind and hail events, which could likely be attributed to microcracks when no glass breakage is found. This problem will not disappear with silicon perovskite tandems, but it can be resolved with thin film manufacturing. Case in point, First Solar is the only major manufacturer to offer a cell crack power loss guarantee due to the resilience of its thin film cells to mechanical stress.

Perovskites have reliability challenges to be overcome as part of commercialization, but these are challenges for both single junction and tandem technology. Beyond microcrack risk, silicon tandems face compatibility issues due to the need to optimize two technologies simultaneously to justify the added cost. How will degradation or discoloration of perovskite top cells affect performance of silicon bottom cells over time? What are the potential power measurement and sorting complications? If different manufacturers are responsible for the top and bottom cell, who will take responsibility for warranties?

It is not clear yet whether tandem startups are positioning as cell suppliers, seeking to be bought by module makers, or establishing their own manufacturing capacity. A simpler, lower cost product made by one supplier appears to be a less risky path to market.

Energy security

From an energy security perspective, developing a component in the United States that supports a product made almost entirely in China does not sound like a winning strategy. As the Inflation Reduction Act's domestic content waiver for Asian silicon and wafers demonstrates, there is little hope the United States will be able to compete with China on silicon. Japan understands this and has invested heavily in thin film perovskite R&D. If the United States focuses only on perovskite-silicon tandem development, it could inadvertently forfeit perovskite technology to other countries.

The United States must build on past successes, not repeat the same mistakes. While US efforts to build a viable silicon supply chain have faltered, cadmium telluride (CadTel) thin-film solar has weathered the storm with a focus on manufacturing innovation and development of a more reliable, responsible supply chain. This is clearly the best way for the United States to compete with China, and perovskites have the potential to leapfrog CadTel on cost with the help of high-speed roll-to-roll manufacturing. Technoeconomic analysis by the NREL indicates capital expenditure for perovskites can be cut in half with a shift away from sheet-to-sheet manufacturing. With strong industry investment and the continued support of consortiums like US-MAP and PACT, we can push that gap even wider and scale United States manufacturing capacity faster than ever.

About the author: Darshan Schmitz has been working as a product manager in the solar industry since 2004. He has managed a wide range of silicon and thin film-based products made in Japan, China, and the United States. Darshan is also active in standards development and has written various publications on the sustainability and reliability aspects of thin film solar.

The views and opinions expressed in this article are the author’s own, and do not necessarily reflect those held by the author’s employer or pv magazine.