Researchers from China's Westlake University, Fudan University and Zhejiang University have explained that while record power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) are usually achieved using organic spiro-OMeTAD, conventional doping with hygroscopic dopants (LiTFSI and tBP) leads to compromised device stability.
Image of spiro-OMeTAD solutions with various dopants alongside filtered 5D spiro-OMeTAD solutions. Image from: Nature Communications
In their recent work, the team introduced a synergistic mixed doping strategy that utilizes a combination of metal-TFSI dopants—LiTFSI, KTFSI, NaTFSI, Ca(TFSI)2, and Mg(TFSI)2—to enhance doping efficiency while effectively removing hygroscopic contaminants from the Spiro-OMeTAD solution. This approach enables PCEs exceeding 25% and significantly improved stability under harsh environmental conditions.
The devices demonstrated a T100 lifetime of approximately 1200 hours under 25 ± 5% relative humidity without encapsulation, a T90 lifetime exceeding 2184 hours at 65° ± 5 °C with simple packaging, and a T90 lifetime over 2184 hours under continuous illumination in an N2 glovebox.
Notably, Ca(TFSI)2 and Mg(TFSI)2 facilitate enhanced oxidative doping, while NaTFSI promotes interstitial doping in the bulk perovskite.
Additionally, KTFSI serves as a catalytic agent, lowering the reaction energy barrier for the other dopants, thereby accelerating spiro-OMeTAD ion radical production.
These findings highlight the potential of synergistic doping in optimizing the performance and longevity of photovoltaic devices and could mark a step towards developing more durable, high-performing organic conductive materials through innovative doping strategies.
