Stable Radical TEMPO Terminated Perylene Bisimide(PBI) Based Small Molecule as Cathode Interlayer for Efficient Organic Solar Cells

By combining stable radical tetramethylpiperidine nitrogen oxide(TEMPO) as end groups and perylene bisimide(PBI) as the core, a small molecular cathode interlayer(CIL) (PBI-TEMPO) was synthesized. Detailed physical-chemical characterizations indicate that PBI-TEMPO can form smooth film, owns low unoccupied molecular orbital(LUMO) level of –3.67 eV and can reduce the work function of silver electrode. When using PBI-TEMPO as CIL in non-fullerene organic solar cells(OSCs), the PM6:BTP-4Cl based OSCs delivered high power conversion efficiencies(PCEs) up to 17.37%, higher than those using commercial PDINO CIL with PCEs of 16.95%. Further device characterizations indicate that PBI-TEMPO can facilitate more efficient exciton dissociation and reduce charge recombination, resulting in enhanced current density and fill factor. Moreover, PBI-TEMPO displays higher thermal stability than PDINO in solution. When PBI-TEMPO and PDINO solution were heated at 150 ℃ for 2 h and then were used as CIL in solar cells, PBI-TEMPO-based OSCs provided a PCE of 15%, while PDINO-based OSCs only showed a PCE of 10%. These results demonstrate that incorporating TEMPO into conjugated materials is a useful strategy to create new organic semiconductors for application in OSCs.