Key Findings
The champion device developed by KIER achieved a power conversion efficiency of 25.24%, with a stabilized power output of 25.1% under one-sun illumination. Other performance metrics include an open-circuit voltage of 1.175 V, a short-circuit current density of 25.83 mA/cm², and a fill factor of 83.21%. In terms of stability, the cells retained over 90% of initial efficiency after 500 hours of continuous operation and 95% during accelerated damp-heat testing at 85 C and 85% relative humidity.
Technical Details
The researchers utilized a catalyst-assisted process employing nickel oxide (NiOx) to manage lithium ions within the hole transport layer (HTL). The process works as follows:
- Nickel oxide powder is added to the HTL solution, where it strongly attracts and dissociates lithium ions from lithium salts.
- The NiOx particles, having captured the lithium ions, are subsequently removed from the solution via filtration.
- This allows for the oxidation of the hole transport material spiro-OMeTAD in under five seconds without requiring the conventional additive 4-tert-butylpyridine (tBP).
The resulting HTL showed a 2.5-fold increase in electrical conductivity and produced more uniform films with improved charge extraction. The test cells were constructed using an FTO substrate, a SnO₂ electron transport layer (ETL), a FAPbI₃-based perovskite absorber, a spiro-OMeTAD HTL, and a gold (Au) electrode.
Background & Context
Conventional perovskite cells use lithium-based salts to increase electrical conductivity and charge transport. However, these additives are volatile; under high temperatures and humidity, they can evaporate or migrate, creating voids and structural defects. Furthermore, uncontrolled diffusion of released lithium ions into the cell interior typically shortens the device’s operational lifespan.
Significance & Outlook
By using a catalyst that is removed after inducing the necessary chemical reactions, KIER has bypassed the stability trade-offs associated with permanent lithium additives. Se Jin Ahn, principal researcher at KIER, stated that this technology marks a milestone for the lifespan of perovskite tandem solar cells. Separately, another KIER team recently achieved a record 26.7% efficiency for a perovskite/CIGS tandem solar cell, as confirmed by the Fraunhofer Institute for Solar Energy Systems.
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