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A perovskite triple-junction solar cell was paired with graphene oxide (GO) and self-assembled monolayer (SAM) bilayer.
Researchers at the Helmholtz-Zentrum Berlin (HZB) in Germany have created a highly complex “triple-junction” solar cell using perovskite. 
The novel perovskite triple-junction solar cell achieved a 27.3 percent efficiency rate. Plus, it demonstrated exceptional stability with no performance degradation over 770 hours of continuous operation.
Stacking layers like a gourmet burger is the secret behind smashing efficiency and stability records. 
“You can imagine it like a Big Mac, where the three buns are separated by different fillings like meat, salad or cheese. Here, that would be the filling between the middle and bottom buns,” explained Prof. Dr Steve Albrecht, head of the Department of Perovskite Tandem Solar Cells at HZB. 
Silicon solar panels have dominated the market for decades, but are rapidly hitting an absolute physical efficiency limit. 
Hence, perovskite is highly important in the solar research world as it is inexpensive and exceptionally lightweight. It can even be mounted on flexible substrates like plastic or fabric.
These cells can harvest far more sunlight than silicon panels by stacking three different perovskite absorbers, with each layer tuned to capture a different band gap in the solar spectrum.
However, perovskite tends to degrade due to a weak link: the polymer layer (PEDOT:PSS) that transports electrical charge between the subcells. This polymer absorbs light inefficiently and breaks down quickly under continuous use. Prompted by this disadvantage, the HZB team tried to replace the layer with a highly stable, low-loss chemical duo.
To maximize efficiency, a complex triple-junction solar cell was made by stacking three perovskite absorbers with varying band gaps. 
The team turned to self-assembled monolayers (SAMs). These are ultra-thin layers composed of large organic molecules that spontaneously organize into a neat single-molecule sheet.
At first, the SAMs failed and couldn’t move the electric charges efficiently on their own.
“We therefore experimented with additional layers beneath the SAM layer to act as a kind of substrate,” said Yeonghun Yun, co-first author and postdoc.
A micro-thin layer of graphene oxide was slid directly beneath the SAM. It completely transformed the interface, creating a perfect morphological and electronic match. Charge transport smoothed out, and optical losses plummeted.
The new triple-junction solar cell achieved a 27.3 percent power conversion efficiency, placing it among the highest values ever recorded for this specific technology.
Even better, it lasts. While older perovskite architectures withered under sustained exposure, the GO/SAM-equipped cell survived 770 hours of continuous operation and retained over 90 percent of its initial performance. This is a monumental stability record in the fragile world of next-generation photovoltaics. 
Typically, tin-lead-based perovskites are highly vulnerable to rapid oxidation and degradation when exposed to oxygen and moisture. The new GO/SAM bilayer created an airtight chemical shield that seals and protects this delicate tin layer from environmental breakdown.
Particularly, this molecular barrier is the key reason the solar cell achieved its 770-hour stability record without sacrificing its performance edge.
The future looks even brighter. According to Prof. Albrecht, this is just the baseline. With minor refinements to the individual perovskite films, the efficiency of this lightweight architecture could easily sail past 30 percent.
The results have been published in the journal Joule on July 9. 
Mrigakshi is a science journalist who enjoys writing about space exploration, biology, and technological innovations. Her work has been featured in well-known publications including Nature India, Supercluster, The Weather Channel and Astronomy magazine. If you have pitches in mind, please do not hesitate to email her.
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