New “nip” perovskite/organic hybrid tandem solar cells with an efficiency greater than 23%

Engineers and materials scientists are working to develop increasingly advanced photovoltaic solutions, to convert as much solar energy as possible into electricity and help reduce greenhouse gas emissions. This has led to the introduction of various new solar cell designs, including all-perovskite tandem solar cells.

Researchers at Chonnam National University in South Korea recently introduced new hybrid monolithic perovskite tandem solar cells based on fully inorganic halide perovskites. These solar cells, presented in an article in Energy and environmental sciencesachieved promising returns of 23%.

“Single junction solar cell designs have some limitations, such as thermalization loss and transmission loss,” Dr. Sawanta S. Mali, first author of the paper, told Tech Xplore. “To solve these losses, we need to make tandem solar cells, in which two absorbers such as wide bandgap (WBG) and narrow bandgap (NBG) materials are stacked together using a layer of appropriate interconnection (ICL).”

Previously introduced solar cell designs based on WBG materials have achieved very promising efficiencies. However, these cells are usually based on hybrid organic-inorganic perovskites, which are not thermally stable and thus compromise their overall performance.

Many of these solar cells are also manufactured using complex processes that are difficult to replicate on a large scale. These include, for example, complex sputtering and atomic layer deposition (ALD) techniques, which can be both difficult to implement and energy intensive.

“In the case of NBG materials, many researchers previously used Pb-Sn-based NBG, which suffer from serious degradation problems, such as Sn.²⁺ to Sn⁴⁺ training,” Sawanta said.

“To avoid these issues, we developed a fully inorganic perovskite-based WBG deposited under ambient conditions using our previously developed hot air method and a polymer bulk heterojunction (BHJ)-based NBG for the fabrication of this two terminal monolithic hybrid tandem solar system “nip” cells (2T-HTSC).These cells can be manufactured using simple ICLs which are free from complicated sputtering or ALD processes.

The main goal of Sawanta’s recent work and study was to realize thermally stable WBG materials that could be processed under ambient conditions and integrated into devices with simple architecture, such as those with a so-called configuration pinching. Ultimately, they made their fully perovskite materials using a hot air-assisted spin coating technique.

When integrated into hybrid tandem solar cells with nip architecture, these materials have been shown to lead to encouraging results. The resulting solar cells achieved an efficiency of 23.07%, with an open circuit voltage of 2.110 V, retaining more than 90% of their initial efficiency for more than 600 hours of operation at their maximum power.

“We have implemented a pinch device configuration and ambient air treatment approach that is simple and suitable for future commercialization,” Sawanta said. “Since these 2T-HTSCs produce better efficiency than a single junction with a very high open circuit voltage (>2 V), we ultimately plan to implement these cells in artificial photosynthesis and agrovoltaic applications or the Internet of Things (IoT).”

In the future, the materials created by Dr. Sawanta S. Mali, Professor Chang Kook Hong and their colleagues could be integrated into solar cells in tandem with other designs, to further evaluate their potential. Additionally, the manufacturing approach employed by this team could be used by other teams to create other robust materials for photovoltaic applications.

“In our recent study, we used only double-junction tandem solar cells,” Mali added. “In our next studies, we plan to implement this concept in triple or multijunction tandem solar cells (MJ-TSC) and their scaling.”

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