Effect of Palladium-Tetrakis(Triphenylphosphine) Catalyst Traces on Charge Recombination and Extraction in Non-Fullerene-based Organic Solar Cells

The effect of the cross-coupling catalyst tetrakis(triphenylphosphine)palladium(0) (Pd(PPh₃)₄) on the performance of a model organic bulk-heterojunction solar cell composed of a blend of poly([2,6′-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,3-b]dithiophene]{3-fluoro-2[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7-Th) donor and 3,9-bis(2-methylene-((3-(1,1-dicyanomethylene)-6,7-difluoro)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (IOTIC-4F) non-fullerene acceptor is investigated. The effect of intentional addition of different amounts of Pd(PPh₃)₄ on morphology, free charge carrier generation, non-geminate bulk trap- and surface trap-assisted recombination as well as bimolecular recombination and charge extraction is quantified. This work shows that free charge carrier generation is affected significantly, while the impact of Pd(PPh₃)₄ on non-geminate recombination processes is limited because the catalyst does not facilitate efficient trap-assisted recombination. The studied system shows substantial robustness towards the addition of Pd(PPh₃)₄ in small amounts.