Engineering And Insight Into The Mechanism For Cathode Interface In Organic Solar Cells

Organic solar cells?OSCs?have attracted extensive attention due to their low-cost,solution processing,light weight,flexibility,and large-area production through roll-to-roll technology.With the research continues to be deepen,the performance of OSCs is constantly improved and the power conversion efficiency?PCE?is constantly refreshed.So far,PCE of single-junction OSCs has exceeded 15%.The enhancement of PCE is mainly attributed to synthesis of new active layer materials,optimization of device structure,control of active layer morphology and modification of electrode interface.Electrode interface between the active layer and the electrode could reduce the extraction barrier of the carrier,polish the contact between the active layer and the electrode leading to an ohmic contact at the interface which is an effective strategy for improving the performance of OSCs.This thesis will focus on engineering and insight in the mechanism for cathode interlayer?CIL?in the OSCs.We have not only revealed the working mechanism of alkali metal fluorides?AMFs?as dopants of zinc oxide?ZnO?in inverted OSCs but also studied the performance and the mechanism surfactant-encapsulated polyoxometalate complexe?SEPC?as a CIL in the conventional OSCs.This thesis is organized as follow:In chapter 1,firstly development history,research progress,working principle and classification of OSCs are summarized.Then preparation of OSCs and the parameters characterizing the performance of OSCs are exhibited.Finally,the types and developments of electrode interface materials are emphatically described.In chapter 2,the mechanism of alkali metal fluorides?AMFs?as ZnO dopants to improve the performance is systematically studied in inverted OSCs.Doping ZnO with AMFs can effectively improve carrier extraction,electron mobility,electron density and built-in potential of inverted OSCs.PCE of the PTB7:PC₇₁BM based OSCs doped ZnO with NaF,KF and CsF as CIL reached 8.64%,8.39%and 8.28%,respectively.X-ray photoelectron spectroscopy?XPS?results show that adding AMFs into ZnO could reduce the oxygen deficiency on ZnO surface.Results of SEM-EDS mapping and XPS depth profiling show that the amount of Na⁺on the ZnO:NaF surface was significantly higher than the amount of K⁺on the ZnO:KF surface and the amount of Cs⁺on the ZnO:CsF surface.So Na⁺have more chances to meet the defects on ZnO surface.Therefore,the devices with ZnO:NaF exhibit the highest PCE.In chapter 3,a novel SEPC-TAPW₁₁-V is applied as a CIL in fullerene?FA?and non-fullerene?NFA?based OSCs.PCE of PTB7-Th:PC₇₁BM based OSCs can reach9.67%,and the maximum PCE of PBDB-T:ITIC based OSCs is 10.67%.It indicates that TAPW₁₁-V is an efficient and universal CIL material for both FA and NFA based OSCs.In addition,results of carrier mobility measurement and capacitance-voltage characterization show that introducing TAPW₁₁-V as a CIL in the OSCs can effectively improve carrier mobility,carrier density and built-in potential.Ultraviolet photoelectron spectroscopy?UPS?show that TAPW₁₁-V not only reduced work function of Al but also was n-type doped by Al,which benefit to increase electron density and electron extraction,thereby improve the performance of OSCs.