An international team of A-list PV researchers spearheaded by the Energy Department’s National Renewable Energy Laboratory has charted a course for perovskite solar cells to push into the commercial market. That’s great news for presidential candidate Hillary Clinton, who envisions that there will be half a billion solar panels in the US by 2020.
If that dream is to become reality, two overlapping things need to happen: solar cells have to be cheaper, and factories have to start churning them out faster and more efficiently.
Yes, Perovskite Solar Cells
For those of you new to the topic, perovskite refers to a class of crystalline materials. Their structure is based on the naturally occurring mineral perovskite, and they can be synthesized easily and cheaply.
Those attributes make perovskite an attractive to substitute for silicon. Silicon is currently the gold standard for high efficiency solar cells, but it is expensive, it is vulnerable to price and supply issues in the global commodities marketplace, and it requires a relatively complicated, conventional fabrication process.
Researchers first took a look at perovskites in 2009 and achieved a conversion efficiency of just under 4%. That’s pretty miserable compared to silicon, but fast forward to 2016 and global efforts have already boosted that figure up to the 15-20% range, topping out at more than 22%.
That amped-up pace of improvement is almost unheard of in the PV (photovoltaic) field, and researchers are anticipating that even more efficiency gains are in the cards.
So, What’s The Problem?
Several major obstacles stand between perovskites and your new rooftop solar array. For one thing, perovskites have a tendency to fall apart when exposed to moisture.
The go-to solution so far is to synthesize perovskites in combination with lead, but that opens a whole ‘nother can of worms in terms of potential environmental and public health hazards.
Some researchers are beginning to experiment with lead-free perovskite solar cells, but that pathway appears to be a long one.
A Perovskite Solar Cell In Every Pot
Apparently, the NREL team is very eager to bring perovskite solar cells to the masses, and they are not waiting for a lead-free version to come out.
In a new paper published in the journal Nature Energy, the team proposed a strategy for commercializing a particularly promising class of halide perovskite cells.
The study, titled “Towards Stable and Commercially Available Perovskite Solar Cells,” outlines the solutions for three challenges:
1) long-term stability
2) a manufacturing method that can produce reproducible, hysteresis-free, high-performance devices
3) reliable device characterization
Hysteresis refers to crimps in the performance of a system due to a time lag between its past and present inputs, and its outputs. The “hys” refers to history (time), not hysteria.
Specifically, the proposed manufacturing method would address grain boundary issues (“grain boundaries” refers to the interface between particles in a crystalline material, where loss of efficiency can occur), and other factors leading to loss of efficiency.
The authors propose using electroluminescence methodology to provide a standard for measuring conversion efficiency.
The study also covers strategies for recycling and re-using the lead used in perovskite solar cells. Here’s the money quote from the abstract:
We believe that perovskite-based devices can be competitive with silicon solar modules, and discuss issues related to the safe management of toxic material.
For the record, the study authors are Nam-Gyu Park of Korea’s Sungkyunkwan University, Michael Grätzel (the “father of thin film solar cells”) of Switzerland’s Ecole Polytechnique Federale de Lausanne, Tsutomu Miyasaka of Japan’s Toin University of Yokohama, and Kai Zhu and Keith Emery of NREL.
Meanwhile, NREL has been busy working on that grain boundary issue. Just last August, a team from NREL and China’s Shanghai Jiao Tong University demonstrated that a method of dissolving crystals called “Oswald ripening” can be deployed to repair defects in low-quality perovskite film, to achieve a conversion efficiency of 19%.
Image (cropped): via NREL.