Researchers at the University of North Carolina at Chapel Hill and Arizona State University and have designed a large-area perovskite-silicon tandem solar cell that achieved a steady-state power conversion efficiency of 25.1% for tandem devices with a large aperture area of 24 cm2.
The team set out to overcome shunting, which is a common issue when scaling up perovskite solar technologies from small-area cells to large-area devices. “Shunts” in PV cells create alternate pathways for a solar-generated charge, leading to power losses. Reduced shunt resistance is associated with multiple forms of module degradation and failure, including hotspots and potential-induced degradation.
The scientists built the 24 cm2 tandem cell with a lithium fluoride (LF) interlayer placed at the interface between a hole transport layer (HTL) made of poly-triarylamine (PTAA) and a wide bandgap (WBG) perovskite absorber. This interlayer is the key element that reportedly improves physical contact at the buried interface and mitigates shunting. The deposited the PTAA and WBG perovskite layers through blade coating.
“Sub-optimal interface contact with substantial voids could act as shunting pathways,” the scientists said in their work. “A LiF interlayer was found to avoid the formation of interfacial voids, which is one possible reason for the reduced shunting of etched tandems with a LiF interlayer.”
The researchers deposited the other layers of the tandem cell by sputtering, thermal evaporation, and atomic layer deposition (ALD). They also tested three different configurations of bottom cells and opted for using
Tested under standard illumination conditions, the 24 cm2 tandem cell showed an efficiency of 25.2%, an open-circuit voltage of 1.89 V, a short-circuit current density of 18.1 mA/cm2 and a fill factor of 0.736.
“This is, to the best of our knowledge, one of the most efficient two-terminal tandem devices reported in the literature with areas of over 10 cm2,” the researchers said.
“The strategy developed here is valuable for developing efficient, reproducible, and large-scale perovskite-silicon tandems,” the scientists said.
