Exploiting Ternary Blends for Improved Photostability in High-Efficiency Organic Solar Cells

Ternary organic solar cells based on polymer donor and nonfullerene acceptors (NFAs) are delivering high power conversion efficiencies (PCE). Now, further improvement needs to be directed to enhance the operational lifetime of organic photovoltaics. Here, we selected three NFAs with different electron affinities and structural properties and found that the most crystalline third component, O-IDTBR, is selectively miscible within the acceptor phase. This reduced trap-assisted recombination and delivered a PCE of 16.6% and a fill factor of 0.76, in comparison to PM6:Y6 binary devices (15.2% PCE). Charge transport and recombination analyses revealed that O-IDTBR acts as a charge relay for improved charge transfer of both donor and acceptor materials leading to a more ordered transport. We find that minimizing trap formation in ternary devices deactivates light-induced traps upon full sun illumination (AM1.5G). As a result, ternary devices do not show any PCE drop in 225 h, in comparison to binary cells which lose more than 60% of their initial performance.