The most important breakthrough in solar cell technology in recent years is the optimization of perovskite solar cells from 3% in efficiency in 2006 to 25% today putting it at the frontier of research efforts in search of an alternative to silicon.
Silicon has traditionally been the material of choice for solar cells due to its high efficiency, long lifespan, and reasonable cost. However, the efficiency of current silicon-based solar cells is approaching the theoretical maximum. On the other hand, perovskite is a relatively new material that has gained popularity in the industry and has the potential to surpass silicon as the top choice for solar cells.
Because of its great promise, researchers have been working to break down a major barrier that has limited its commercialization, namely, the short lifetime of the cells. Typical perovskite devices degrade within minutes or hours to non-functional states. This is because they are easily susceptible to atmospheric moisture, oxygen, extended periods of light, or high heat. At the present, a significant part of the solar research community has been largely focused on increasing the operational lifetime of perovskite cells to competitive levels with traditional solar panels that can last up to 30 years.
In December 2022, researchers from the University of New South Wales in Australia announced that they had discovered a low-cost sulfur-based additive (the 1-DDT or Dodecanethiol) that could boost the stability of perovskite solar cells without compromising efficiency. The additive not only stabilizes the lithium in the hole transport layer of perovskite cells to improve efficiency, but it also promotes oxidation and prevents water infiltration, which further enhances stability.
The perovskite cells made with this new additive showed impressive stability, retaining more than 90% of their initial efficiency after operating at maximum power point under one sun illumination for 1,000 hours, and more than 93% of their initial efficiency after remaining at open circuit condition under one sun illumination for 2,000 hours. This level of stability is the best reported in Australia and among the highest globally.
Also, until now, lead acetate had only been used to make methylammonium or cesium-based perovskites, which are relatively unstable and not suitable for real-world applications. A team of Chinese researchers found that a better candidate for commercial use can be found in perovskites made using formamidinium and caesium, thanks to their superior stability. According to the researchers, the cells demonstrated a conversion efficiency of 21%, which is the highest efficiency ever recorded for a device made from a non-halide lead source. When incorporated into a mini prototype solar panel, the cells achieved an efficiency of 18.8%.
In December 2022, scientists from the University of Oxford, Monash University, and the US National Renewable Energy Laboratory (NREL) said they have found a way to create stable perovskite solar cells with fewer defects, bringing them closer to the durability of silicon. The researchers used a new fabrication method called DMF/DMACI, which replaces the solvent dimethyl-sulfoxide in the commonly used DMF/DMSO solvent preparation method with dimethylammonium chloride (DMACI) as a crystallization agent. This allowed them to more effectively control the intermediate phases of the perovskite crystallization process, including texturing, orientation, and the crystallinity of the perovskite. Read more here.
Tandem Solar Cells
The capital solution that has been embraced by the most researchers is the use of a combination of both silicon and perovskite in tandem solar cells. These cells have been shown to be more efficient than either material used alone because they can effectively capture different parts of the solar spectrum. Perovskite is better at absorbing blue light, while silicon excels at capturing red and infrared wavelengths. By combining the strengths of both materials, tandem solar cells can harness more energy from the sun.
The crown of these efforts was when in December 2022, a team at Helmholtz Zentrum Berlin (HZB) announced that they have developed solar cells with an efficiency of over 32%, breaking the previous record of 31.25%. This new achievement, which has been verified by the National Renewable Energy Lab, is currently the highest of any emerging photovoltaic technology. This significant advancement brings the technology into a new realm.