Optimized Interface Properties For Organic Solar Cells Based On Regulation Of The Polar Groups In Electron Transfer Layer

Polymer solar cells?PSCs?have drawn significant attention due to their potential for low cost,light weight,printable,and high-throughput solution processing.At preaent,During the past decades,plenty of excellent active layer materials have been designed and synthesized.The power conversion efficiency?PCE?of PSCs has surpassed 16.02%.However,there are many problems to be solved for realizing the commercialization of PSCs.In order to solved those problems,in despite of the design and synthesis of active material,or optimize a desirable device structure,and to design an excellent interlayer which can improve the device of efficiency and stability.Based on current researches,conjugated polyelectrolytes have been employed as one of the most distinguished organic interlayers to improve electron injection or extraction.Most of CPEs can form a favorable dipole moments at the interface,due to the various polar groups attached on the main chain.At the same time,the polar groups can create favorable dipoles at the electrode/active layer interface,which was critical for the CPEs to minimize the interfacial energy barrier.In this woork,we will study the effect of ionic groups on CPEs.Herein,three new self-doping n-CPEs based on diketopyrrolopyrrole?DPP?alternated fluorene framework were reported.The effect of the number and location of polar groups on the properties of the new n-CPEs has been systematically studied.It can be found that the photoelectric properties of n-CPEs were sensitive to the number and location of polar groups.A tunable work function?WF?,interfacial interaction and conductivity of these n-CPEs can be readily realized by regulating the number and location of polar groups on the electron skeleton.The polar groups directly appending on electron-withdrawing DPP unit can promote a stronger n-type self-doping and lower WF than the ones attached on electron-pushing fluorene unit.Increasing the number of the polar groups can further optimize the photoelectric properties of conjugated electrolytes.As a result,incorporation of new n-CPEs as cathode buffer layer,the PSC performance was significantly improved to 8.3%for fullerene system and 10.57%for non-fullerene system,respectively.These results demonstrated that without complex molecular design,simply regulating the number and location of polar groups of the n-CPEs can provide a facile way to develop highly-efficient cathode interlayers for high performance polymer solar cells.Secondly,in order to further improve the stability of the device,on the bsis of the first work,the Br^-in PDPP-FNBr were exchanged with hydrophobic bis?trifluoromethanesulfonyl?imide?TFSI?and bis?pentafluoroethanesulfonyl?imide?PFSI?.The electron transport layers PDPP-FNf₃ and PDPP-FNf₅ have the same backbone structure of alternating copolymerization of DPP and hydrazine,but the number of F atoms in the hydrophobic polar group is mainly different.It is used as electron transport layer in the solar cell device of PM6:IT-4F.