Researchers in China developed a monolithic perovskite-silicon tandem solar cell using a steric-complementary interface design, achieving a certified efficiency of 32.12% and improving long-term stability. This strategy optimizes the molecular fit in the perovskite lattice, improving both charge transport and device lifetime.
A group of researchers led by China Soochow University has fabricated a monolithic perovskite-silicon tandem solar cell with a interface design based on steric complementarity, aimed at improve device efficiency and reliability.
Steric complementarity defines how well the three-dimensional shapes of two molecules fit together without causing steric clashes, which are spatial overlaps that are physically impossible due to the sizes of the atoms. In perovskite solar cells, steric complementarity is key to the efficiency and stability of the material, which depends on how well the components in the perovskite lattice fit together.
“We have introduced a new strategy at the molecular level that goes beyond just combining different molecules,” said the study’s lead author, Wenhao Li. pv magazine. “By purposefully selecting a pair of molecules with a significant difference in size – a small, flexible piperazinium (PipI) cation and a large, stiff phenethylammonium (PEAI) cation – we created a synergistic effect.”
Li explained that the tiny PipI infiltrates deeply into the perovskite surface to neutralize atomic-scale defects that are inaccessible to larger molecules, while at the same time the bulky PEAI self-assembles into a robust, hydrophobic “canopy” on top, providing excellent protection against environmental stressors.
Through their Steric-Complementary Synergistic Strategy (SCSS), which reportedly solves the structural trade-off between deep-level chemical passivation and the physical shielding required by the perovskite absorber, the researchers built the top perovskite cell of the tandem device.
It was fabricated with a substrate made of indium tin oxide (ITO), a hole transport layer (HTL) made with a self-assembling monolayer known as 4PADCB, a perovskite absorber, the PMEAI passivation layer,an electron transport layer (ETL) that relies on buckminsterfullerene (C60), a tin oxide (SnOx) buffer layerand a silver (Ag) metal contact.
Tested under standard lighting conditions, the device achieved an energy conversion efficiency of 22.26%, an open-circuit voltage of 1.270 V, a short-circuit current density of 21.50 mA/cm2 and a fill factor of 81.52%. “This result demonstrates that SCSS can simultaneously suppress non-radiative recombination and optimize charge transport,” the academics pointed out.
The tandem cell, which is built with the perovskite device and a bottom heterojunction (HJT) silicon cell, achieved a maximum energy conversion efficiency of 32.3% and a certified return of 32.12%.
“This performance is among the highest reported for this technology, demonstrating the power of our approach,” said Li. “The devices also demonstrated excellent long-term durability, retaining more than 80% of their initial efficiency after 1000 hours of continuous use under maximum power point tracking. This shows that our strategy not only increases efficiency, but also significantly improves the lifespan of devices.”
The new cell design was introduced in “Steric-complementary synergistic strategy for highly efficient monolithic perovskite/silicon tandem solar cells”, published in Advanced functional materials.
“In summary, our study establishes a generalizable interface design principle based on steric complementarity that provides a promising path toward highly efficient and operationally stable perovskite-based tandem solar photovoltaics,” Li concluded.
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