Investigation Of Carboxyl-functionalized Materials: Quaternary Amine Graphene Quantum Dots And Cesium Salt Of Pectin As Cathode Interlayer For Organic Solar Cells

Recent years,organic solar cells?OSCs?have received academic interests due to the advantages of low weight,flexibility,solution processibility and large-area processibility.In the past decades,the power converse efficiency?PCE?of bulk heterojunction organic solar cells has break 13%due to the development of new photoactive layer materials.However,in order to make OSCs become truly practical low-cost photovoltaic technology,the stability in air and the PCE need to be raised to a better level.Therefore,developing easy synthesized cathode interlayer materials with suitable energy levels and solution processibility are very important.In this paper,we develop two new cathode interlayer materials through functionalizing their carboxyl groups.The main results obtained are as follows:1.To prove the practicability of the carboxyl-functionalized material decreasing the work function of cathode,we functionalize the carboxyl groups of graphene quantum dots by a two-step reaction and obtain new quaternary amine graphene quantum dots?GQD-NI?cathode interlayer material.In PCDTBT:PC₇₁BM system,solution processed GQD-NI layer shows a PCE of 7.49%and better than common cathode interlayer,Ca.Because of the high conductivity of GQD-NI,PCE remains 5.55%when the thickness of GQD-NI is up to 36 nm.This means GQD-NI may be beneficial for the future large-area devices.When the photoactive layer changes to PCE-10:PC₇₁BM,GQD-NI show better PCE than Ca,which proves GQD-NI have general applicability.2.In order to obtain easy synthesized,low-cost organic cathode interlayer material,we choose the natural polymer,pectin,to functionalize its carboxyl groups by one-step neutralization reaction with Cs₂CO₃ and develop cesium salt of pectin?PeCs?cathode interlayer material.In PCDTBT:PC71BM,solution processed PeCs shows a PCE of 7.14%and better than common cathode interlayer,ZnO and PFN.In non-fullerene photoactive system,PBDB-T:ITIC,PeCs remains good performance and has general applicability.As a natural polymer derivative,PeCs fills the blank of natural polymer materials hardly used as cathode interlayers and shows a new strategy for future development of cathode interlayers.