Gianluca Coletti, an expert in perovskite-silicon tandem technology, explains what kind of cycles the photovoltaic industry and the scientific community experience every time new jumps in power conversion efficiency occur at the cellular level. According to him, the turnover of efficiency records is much faster, which is typical of the early development stage of a new technology with incredible potential.
Many called this the psychological barrier of 30% technology: a kind of initiation for perovskite as an emerging technology.
Perovskite is a new material structure that quickly took the photovoltaics world by storm – a world that is often not “touched” by breakthrough innovations. However, perovskite solar cells, due to their ease of processing and unique properties, have been massively investigated in academic and commercial laboratories. Not just a few, but thousands of scientists around the world began to improve knowledge and achieve new efficiency records with this new material. Only ten years after its introduction, a laboratory record of 25% was achieved in photovoltaics with a single material (single junction) device. Exceeding the efficiency limit of any single material device (name it: silicon, perovskite, CIGS, etc.) while maintaining an affordable potential is the most important gap the PV community wants to fill. For now, this is only possible if two materials are used to convert light into electricity instead of one. The main candidates are silicon and perovskite. Silicon is the current TW-scale material for energy transition and perovskite due to its tunable material properties and potential low cost. The combination offers the possibility of achieving more than 30% efficiency in a low-cost and large-scale scenario. Once these two materials were available, the community witnessed a rush to smash the 30% efficiency limit: the “30% rush”!
In 2022, not once but several times, the 30 percent barrier was broken by combining these materials. First, Swiss researchers at CSEM/EPFL, then TNO, TU-Eindhoven, imec and TU-Delft collaborators at Solliance, and finally Helmholtz-Zentrum Berlin, which demonstrated over 32% conversion efficiency with its tandem cells. Just last April, KAUST researchers moved the limit to 33.2 percent.
The PV community was not new to 30% transmission, see for example III-V semiconductors developed mainly for space applications, but this is the first time this efficiency has been achieved with materials with affordable potential such as compound. of silicon with perovskite.
Previous PV congestion
Was this the first “rush” in the PV community? Absolutely not. Looking at the NREL world champion efficiency chart, it is clear that there were also similarpatterns at around 20% and 25% efficiency. How do you recognize these periods? Note the increase in cell record efficiency just before the milestone is reached.
In recent years we have seen the “ultimate” rush. The goal is to achieve the highest efficiency from a single-material silicon solar cell, which has a theoretical limit of about 29%. The goal here would be to get the final and highest record. The most recent efficiency record is held by Long at 26.8%, and many companies plan to beat this soon.
After reaching a historically significant record, the development seems to be slowing down. After the 20% rush, there was a 10-year period when no new record was reached. Accordingly, there was a 20-year gap after reaching the 25 percent threshold.
So what happens in the PV community between each big board? In order to understand it, it is necessary to look not only at the laboratory’s efficiency chart, but also at the manufacturing and installation trends. Most of these records are achieved in small areas, in research environments. The next step is to scale to large areas to simplify processing and manufacturability and ultimately to mass production. This requires the efforts of universities, research institutes and companies. Just as an example, about 12-15 years ago researchers focused on developing a new n-type silicon-based cell concept. Then, the rule of thumb was that a new cell architecture was not even considered until its efficiency was over 20% in the 6-inch wafer region (at the time, the lab record was 25%). This rule was intended to demonstrate the importance of large area rather than “only” laboratory efficiency. After a busy period, research is focused on bridging the gap between laboratory records and the efficiency of mass-produced cells.
If history repeats itself, already starting this year, large resources will be focused on the industrialization of perovskite/silicon tandem cells and modules. There are four major challenges to implementing commercial tandems. First, based on record technology, the most efficient stack of materials must be scaled to industry-relevant sizes (more than 100 s cm2). Second, the reliability of such a wide-area device must be proven under appropriate outdoor conditions. Third, all possible technologies need a detailed techno-economic cost-benefit analysis and manufacturing feasibility, and (hopefully) a full life cycle analysis. This includes material availability and new tools for depositing perovskite and transport layers. Finally, large-scale manufacturing of a reliable, cost-effective, fully integrated tandem cell and module – with high-performance tooling and abundant materials must be demonstrated for the technology to be viable. Only then would a 30 percent rush have completed the cycle.
Of course, there is always a new threshold for the scientific community after a new great record. And for tandem devices, the cycle of efficiency records is much faster, which is typical of the early development of a new technology with incredible potential. How long do you think it will take for the solar community to reach 35%?
Gianluca Coletti is Associate Professor at the University of New South Wales Sydney and Program manager Tandem solar technology and applications at Netherlands Organization for Applied Scientific Research (TNO), which is currently seeking to market a two terminals (2T) within the perovskite-silicon tandem solar cell technology a a four-year research project called FIT4Market.