Research On The Application Of Polyethyleneimine In Organic Solar Cells And Lithium-ion Batteries

Organic solar cells(OSCs)and lithium-ion batteries(LIBs)have energy conversion and storage functions,respectively,and are research hotspots in the energy field.Polymer interface modification has a regulatory effect on the charge transport at the interface of OSCs and LIBs.Polyethyleneimine(PEI)has abundant amine groups,which can improve the interface transport behavior of electrons and ions.In this thesis,PEI is used for the interface modification of OSCs and the modification of the binder of the silicon anode in LIBs to improve the performance of these two types of devices.Main research results are presented as follows:First,limited by the Michael addition reaction between the amine groups of PEI with non-fullerene acceptor materials,it is difficult to realize high-performance non-fullerene OSCs with alcohol solvent-processed PEI or ethoxylated polyethyleneimine(PEIE)interfacial layer.To solve this problem,it is proposed to reduce the reactivity of the non-fullerene acceptor materials with PEIE by reducing the film thickness of the PEIE interfacial layer.When the film thickness of PEIE is reduced to 1.2-1.3 nm,alcohol solvent-processed PEIE can be effectively used as the interfacial layer of OSCs such as PM6:Y6:PC₇₁BM solar cell,and the power conversion efficiency(PCE)of the device can reach 15.3%.The non-fullerene active layer has a very different requirement for the film thickness of the PEIE interfacial layer from the fullerene active layer.In PM6:Y6:PC₇₁BM non-fullerene OSCs,increasing the film thickness of PEIE to 5 nm,the PCE of the devices will quickly decrease to 7.5%.But,for fullerene device,the device with 5 nm PEIE shows the best PCE.It is found that the strategy of reducing the film thickness of PEIE is not applicable to some non-fullerene acceptor materials with higher reactivity.Second,tandem device is considered to be an effective approach to break through the Shockley-Queisser efficiency limit of single-junction OSCs.Zn O NPs is widely used as an efficient electron transport layer(ETL)in interconnecting layer(ICL)for tandem OSCs.However,it is found that the photocatalytic effect of Zn O NPs would destroy and decompose the receptor materials in the organic active layers,and seriously affect the light stability of the device.To solve this problem,PEIE is selected to replace Zn O NPs and build an ICL of PEDOT:PSS/PEIE.Compared with PEDOT:PSS/Zn O NPs,single-junction solar cells with PEDOT:PSS/PEIE as the interfacial layer not only have slightly higher PCE,but also have significantly improved light stability under AM 1.5 G illumination(100 m W cm^-2).The device with PEDOT:PSS/PEIE interfacial layer remains about 80%of its initial PCE after 160 h illumination.Where the device with PEDOT:PSS/Zn O NPs interfacial layer remains only 47%of its initial PCE after 160 h illumination.With the PEDOT:PSS/PEIE as the ICL,nonfullerene tandem OSC with high PCE of 16.4%is obtained.Third,binder is an important part of LIBs,and improving its ion and electron transport capabilities is of great significance for obtaining high-performance silicon anodes in LIBs.However,binders with good lithium ion and electron transport properities are very limited.Therefore,polymer binders with high ion and electron conductivities are prepared by assembling ionic polymers(PEO and PEI)onto the conducting polymer PEDOT:PSS chains.Crosslinking,chemical reductions,and electrostatics increase the modulus of the binders,thereby helping to maintain the integrity of the electrode and inhibit the excessive growth of the solid electrolyte interphase(SEI).The polymer binder shows lithium ion diffusivity and electron conductivity that are 14 and 90 times higher than those of the widely used carboxymethyl cellulose(with acetylene black)binder,respectively.The silicon anode with the polymer binder shows a high reversible capacity of over 2000 m Ahg^-1 after 500 cycles at a current density of 1.0 A g^-1 and maintains a superior capacity of 1500 m Ahg^-1 at a high current density of 8.0 A g^-1.